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MG Midget and Sprite Technical - DIY rear disc brake conversion - CNC volunteer?

So, I have been pining after rear discs for a while, but am loathe to pay a grand or more for a kit. The quandary presents what Mr. Holmes would call "a two pipe problem."

I note that Frontline's kit requires welding a parking brake cable bracket to the rear axle. That's no good, as I don't have a welder, and it seems like they should have been able to source a caliper that doesn't require cables all the way back. I had seen older threads here and elsewhere that discuss using Nissan calipers (various models), and I believe the Old Phartz kit uses the original brake rod setup, so I grabbed my calipers and went down to the pull-and-pay for a look-see.

It turns out that you can use both the calipers and 9.20" rotors from a 1996 Nissan Sentra (I am assuming solid wheels with 4x100mm bolt pattern), and hook the little parking brake levers right up to the existing brake rod setup on the Spridget. Only trick looks like making or sourcing a different caliper parking brake lever, such that the short pull begins closer to twelve o'clock (as one looks at the shaft end-on), and with a hole to receive a ball-and-joint brake rod end, instead of the existing hook to receive a cable end. Of course, you'd need new, adjustable or cut-to-length and threaded brake rods. No big deal.

Another alternative that may not require new brake levers would seem to be 1981-84 Nissan Maxima calipers, such as these guys used: http://www.britishv8.org/Articles/TR6-Rear-Disc-Brakes.htm They appear to have the brake levers in something very close to the correct orientation to receive a yank from the existing rods. All one would need to do is make a new end to fit--a matter of cutting, threading, and finding a suitable end piece.

After I get my EFI setup working this winter, I will be doing this conversion, which using pull-and-pay calipers and a $4 rebuilt kit, would be around $50~60 for calipers, $8 for the kits, $24 for rotors, and new hoses for $26. Grand total? Less than $120 for parts (though I left out brake fluid and some bolts), plus a chunk of 6061 aluminum from Metal Mart or wherever to make a 'J' bracket to mount the things.

My only question is whether anyone handy with CNC software feels like making a file to cut the mounting brackets for us DIY folks, to save us the trouble of hand-cutting brackets from a chunk of 6061. I see that the nice fellows on the above TR6 write-up make available their CNC file for free. Seems like an adept CAD user could quickly alter that file to make the brackets for our Spridgets. Any takers?
JM Young

Wow....cool research...nice job,

How where you able to deduce that we needed a 1996 nissian to make a rear disk brake set up...was it just pure dumb luck ir is there a method to the madiness


Prop


Prop and the Blackhole Midget

Hey, Prop.

Well, it was a combination of searching MG-related threads to see what people had already tried, and hard work.

As to the latter, I knew that 9" or smaller rotors were needed, as 10" and above are too large to clear 13" wheels (including the caliper width). So, after Google searches did not yield a viable 9" rotor, I laboriously waded through every rear rotor sold by Autozone on their website, and narrowed down the half-dozen candidates first by bolt pattern (4x100mm) and by 'hat' depth sufficient to set the rotor disc back from the (in my case, minilite) wheels to allow for caliper clearance.

Then, I just put the Autozone rotor number into a cross-reference chart I found on-line, Googled a few of the recognizable brands' part numbers, and... voila! A handful of hits appeared showing Nissan models using that rotor. Then, I just looked those models up on Autozone's website and checked out their calipers to see which ones might have a viable, cable-operated parking brake configuration and bleeder valve orientation (gotta be up).

Note, however, that there are three or four calipers that might work, and I have yet to decide for sure whether the 1996-98 Sentra caliper is better than the 1991-94 version (though the bleeder looks better), or whether the Maxima caliper is better than, say, a 280ZX. So, while I'm pretty sure the Sentra or Maxima caliper would involve the least amount of fiddling about to get the parking brake to work, you might ultimately disagree.

Still, I *am* interested in hearing whether I'm going to have to hand-cut a set of adapters, or if someone might be interested in modifying the non-proprietary CNC file offered by the TR6 folks to produce something for our Spridgetly purposes.

Joel.
JM Young

JM Young,

A quick look at the TR6 page shows that they refer to a CAD file, which is different to a CNC file. The CAD file would describe the item in either 2D or 3D and may be of a proprietry format requiring a particular package or may be a more generic format easily loadable into many packages. A CNC file usually means the actual G Code the machine tool uses to generate the part and would not be readily converted. If the CAD file is 3D then it can easily be modified with the appropriate package and then post processed to produce the CNC file to produce the part.
David Billington

Easiest would be to make one adapter by hand and note the critical dimensions after the test fit. Then it would be easy to draw the part and generate the G-code for the tooling operations. I'll do it if you get to that point.
Trevor Jessie

Trevor does great work in this field, he made a part for me and it worked ... I wanted to mention him, but I felt I might be interfering ... plus he is state side, so not sure how that works.

Should be interesting to see what you 2 come up with.

Good grief joel, that is insane...that was certianly not a sunday afternoon project...

Ill say one thing, if you want rear disc brakes ...by god your going to get them....haha

Prop
Prop and the Blackhole Midget

Calipers: We have used MGF rear calipers in our conversion. Being RWD the sizing is better than most FWD rear calipers. Handbrake is dead simple - there's a hole in the end of the lever to take a clevis pin and it requires a transverse pull in towards the centre of the car - just like the original midget set-up does. The rods may have to be shortened but certainly no brackets to weld to the diff and subsequent straightening to get it true again.
And the piston size is in the right ball bark - though as with all brake conversions you need to check & adjust front:rear balance.

Here's the one on our MGB: http://www.mgparts.co.nz/about-us/our-cars/joseph-s-rear-disc-brake-conversion/ Our Midget set-up is very similar, though it is positioned behind the axle as per usual rather than ahead of it like the B one had to be in order to clear the fule tank guard we use when rallying.
Paul Walbran

PS We cut the outside of the adaptor plates on a bandsaw and machined the inside on a lathe, no real challenges there.
Paul Walbran

David,

Thanks for catching my error, and for the explanation of the design-to-manufacturing process. That's a big help.


Paul,

I didn't see your contribution to the following thread in my original search: http://www.mg-cars.net/mg-midget-sprite-technical-bbs/disc-brake-rear-2014010320143025842.htm Thank you for pointing us to your excellent project. The specs as to the oil catcher recess will be especially helpful, if I use one. I hadn't noticed a similar recess on the Frontline and other kits' brackets, but perhaps the images just don't reveal that feature.

One question. When hand-cutting the prototype bracket, and assuming I were to include an oil catcher recess, would the large central hole and recess be the first operation, as opposed to cutting the outside profile on the bandsaw? I'm wondering what shape for the blank aluminum plate is best to facilitate a machine shop's task of creating the recess on a lathe? Round? Square? Unimportant? I'm unfamiliar with how much metal they'd need to grab the plate with the lathe.

Caliper selection.

As nifty as the MGF caliper is, I am intent on designing a setup with parts (and cores) readily available in bone yards on this side of the pond. The biggest challenge would seem to be the mounting brackets that allow the MGF caliper to 'float'; the calipers themselves seem widely available on the net. That said, the Nissan calipers I plan to use (see below) are available worldwide, so the brackets I'm anticipating would be useful to all Spridget owners.

Also, once you add up the cost of rebuilt MGF calipers, core charge, mounting brackets not available in U.S. yards, and shipping, the cost of parts is more than double the Nissan-based package-assuming one can find wrecking yard calipers, of course.

As for parking brake actuation, I went back to the local pull-and-pay today (customer appreciation day means a free cheeseburger) and found a pair of 1995-98 240SX calipers, which have the cable lever pull in the right orientation--toward the differential, as seen in the attached image. Moreover, the bleeder valve will be the highest part of the caliper when mounted on the car (caliper in this image would be driver's side, back of hub). Nice to be able to easily bleed the system without removing the calipers for future maintenance.

I think a simple retainer clip to keep the clevis pin from slipping off the hooked end would be easy to source or even easier to bend up. I'm starting to envision a configuration that would work well as I type these words. The parking brake pull is quite short on these calipers, by the way, so I don't think there would be a large tendency for the clevis pin to escape the hook.

As for cost, the calipers with mounting brackets, parking brake cable brackets (perhaps useful as a guide for the rods), and bolts were $60. Rebuild kits on Autozone are $12 each side and more complete than cheaper kits. Add $32 for a pair of hoses and $25 for new rotors, and we're talking $141 all in.


Trevor,

I am interested in collaborating with you on this project--thank you for offering. If you would please email, let's work out the details, such as whether to include the oil catcher recess, an appealing and functional profile for the bracket, etc. I am heading out to the local Autozone right now to get a set of rotors and pads to make sure the Sentra rotors with the 240SX calipers will clear my 13" minilites before we go any further.


Prop,

Yes, this is something I've been wanting for quite some time--and sifting through every rotor on Autozone's website took me something like an hour (sitting on the recumbent bike, so I got a workout in, too). Pretty mind-numbing work. I hope Trevor and I can produce a set of brackets that will help DIY Spridget owners step up to rear discs inexpensively and with a minimum of hassle.

Joel.

JM Young

We made the alloy plate basically circular on the outside apart from the lug to carry the caliper. We were tempted to prune a bit of unnecessary weight off, but the circle made it much easier to grip in the lathe.

We cut the outside profile first, then roughed out the hole in the centre with a hole saw, then swung it in the lathe to machine the inside detail to size, including accurately sizing the hole so it would spigot on the small ridge on the axle.

Understand about availability, have to be practical. MGF calipers are plentiful here and in the UK and provided they haven't been off the car too long usually don't need overhaul so they are a simple choice for us. The carrier in which the main caliper body floats is part of the caliper, and the carrier's mounting holes are already tapped, so all you have to do is drill 2 holes in the plate in the right place and bolt the caliper to it.
Paul Walbran

Paul,

Thanks for the added detail on the procedure.

Regarding the MGF caliper, a few things.

First, this Autozone part looks suspiciously similar to the MGF part: http://www.autozone.com/autozone/parts/Duralast-Reman-Brake-Caliper-Rear/_/N-8knrp?itemIdentifier=718783_0_0_

Here is the MGF part on the Rimmer webpage: http://www.rimmerbros.co.uk/Item--i-SMC000460R

I wonder if you think these are essentially the same. I am having trouble locating a cross-reference chart (but still looking).


Second, in trying to answer the above question, as you can see, I located a website that lists the carrier as well as the caliper. So, I can certainly obtain the carrier (happy to be wrong about that). They also have greenstuff pads, which are what I run up front. So, I can obtain the parts need to use the MGF caliper--the increased cost aside.


Third, if I were to use MGF calipers, what I am concerned about is the size and configuration of the pads. The 9.20" (234mm) rotor I was planning on using has a relatively narrow, raised bedding surface--32mm. My trip to the store yesterday reveals that even the relatively small pads from the 240SX caliper end up partially off that ring--toward the hub. Now, perhaps that doesn't matter, as the pads might simply wear for a bit until there was a slight 'step' in the pad material, after which the whole pad would be contacting steel. Not really as things should be, though, since I'd be losing some of the pad surface and braking efficiency.

The rotor listed by Phil Lawson is 239mm, which would be very a close fit indeed inside a 13" minilite, and it does seem to have a wider bedding surface that extends farther inward toward the hub. However, it has only a 65mm bore for the protruding bulge on the end of the Spridget half shaft: http://www.oscaroparts.com/brembo-disc-brake-rotor-08-4177-10-180301-1896-p

That would make it the same as this Autozone part number: http://www.autozone.com/autozone/parts/Duralast-Brake-Rotor-Rear/_/N-8knrr?itemIdentifier=48752_0_0_

I don't think that is sufficient for a Spridget, as the 68mm bore on the rotor I've got is just b-a-r-e-l-y going to work, if indeed it works at all. I haven't yet removed the brake shoes and wheel cylinder to make sure the bevel on the back side of the bore is sufficient to accommodate the half-shaft's bulge, but will do that shortly.

What I'm getting at is this. To avoid resorting to the 1996 Nissan Sentra caliper, whose pads are tailored to fit that narrow bedding surface--and which would require me to fabricate a new brake lever--I'll need either a rotor closer to 9" with a broader bedding surface (and sufficient bore), or a different caliper than the 240SX that features narrower pads.

Infuriatingly, Rimmers does stock the spring for the brake lever, but not the lever itself. Otherwise, I could perhaps use the MGF lever on the Nissan Sentra caliper and be done.

There are no specs on the Rimmer website for the dimensions of the MGF pads: http://www.rimmerbros.co.uk/Item--i-SFP000360 So, I wonder if you know their height--the dimension from the outer edge of the rotor to their innermost edge? Again, the bedding surface on the rotor I've sourced is 32mm.

Thanks so much for all of your input. Naturally, I'll be sharing the solution, whatever that turns out to be, with everyone on the forum.

Joel.
JM Young

I'll try to email you latter, but you should not design based around the machining process. Design what works, and then decide how to machine it or alter it so that it can be more affordably machined.
You could even do your mockups in wood.

Trevor Jessie

Trevor,

Unless this is too late, please use my home email (I've tried unsuccessfully to change it on this website), which is jmyounghome@gmail.com I am trying to establish 'degrees of separation' between work and home, and the @swcp.com address has morphed into the work address.

Very well, thank you - I will focus on the physical configuration first. I'm excited about coming up with an elegant Spridget solution but prefer to proceed methodically rather than rush and create additional hurdles down the line. I am still addressing a handful of challenges, as you saw above, and have some images too large to post that I can send via email for discussion--such as the rotor with caliper inside the minilite, the 240SX pad's slight overhang on the Sentra rotor's bedding surface, etc.

A mock-up in wood or perhaps MDF would be excellent, as I have a decent compliment of woodworking tools--planer, router table, drill press, etc.--and could 'machine' all aspects using tools on hand. Great suggestion.

Joel.
JM Young

Trevor,

Well, nix on the 240SX calipers, as with Maxima and a few others. The NX has pads of the same dimensions as the Sentra's (uses the same rotor), but the lever would be in a less advantageous position vis-a-vis the bleeder valve.

So, I'm going to use the '95-98 Sentra calipers, after all. Relatively simple 'L' brake actuation lever to fabricate, but no biggie. I suppose those could be CNC'd as well, although I wonder about the 6061 rounding out over time, as opposed to stamped steel levers, if I can't source some.

Next step is to remove brake shoes and one wheel cylinder, to make sure the bezel inside the rotor hub bore is sufficient to fit the Spridget half-shaft central bulge. Won't happen this week, as she's my daily driver. Perhaps next weekend early one morning.

Joel.
JM Young

Joel, sorry I was playing in the B all day yesterday, and working all day today.
I think the main issue is to go for what's readily available. Where you are, that sounds like the Nissan calipers, where we are, they might be too, but so are MGF and it's nice to keep it in the family. I imagine that in the UK MGF would be much easier to get. So horses for courses.

That said, the MGF pads are 38mm pad depth radially. there's also a 2mm lip of backplate inside of this.

As fat as the centre hole goes, I would have though that would be a snip to open out to the required size. Ideally the discs would slip straight on, but the PCD is different so some machining is needed anyhow.

I intially wondered about the 32mm, it's quite narrow and really just a front wheel drive sizing so could be undersized. Then I thought about the conversion on my B, also using MGF pads. A much heavier car, and when rallying on gravel with codriver, spare wheel, tool box (bolted down) the weight distribution is about 45% front 55% rear. In addition, on gravel you want a great deal of rear bias to flick the rear end out, and there is less weight transfer than on tarmac - so all told in these curcimstances the rear brakes are working harder than the front. Despite this, they have been well up to everything thrown at it (admittedly on 1166 pads and 260mm discs) in circumstances that previously would completely consume a set of high spec rear brake shoes within a couple of special stages. (And leave no linings at all and pop the hydraulics, hence the change).

So if 38mm pads handle this, then 32mm pads should handle a Midget used on tarmac.
Paul Walbran

Joel, how are you centering the rotor on the wheel? I was assuming that it was going to be redrilled to the 4x4" pattern, in which case it would be no big deal to open up the center hole a bit if required. I think you are undertaking an interesting project, but I think you are going to learn why Steve (OlPhartz) charges so much for his kit.
Trevor Jessie

Paul,

No apologies necessary. I wouldn't dream of interfering with your B-driving pleasures.

Yes - I like the symmetry (or whatever) of using MG parts, but indeed it's more convenient to use Nissan bits over here.

Thank you for taking the time to pull pad measurements. I'm glad to hear you think the braking area should be sufficient.

Please note that the 32mm measurement was the width of the rotor's bedding/pad contact area; the Sentra pads themselves are 29mm wide (radially), and 82mm long. Kind of a cheshire cat smile sort of pad. So, I believe that yields a 2378mm surface area per pad. I'm thinking that should be sufficient, given the more modest needs of a street Spridget, but I also hope it's a step up from OEM drum brakes, in terms of force and fade reduction.

Sorry, what is 'PCD'? I am unsure what sort of machining you are suggesting would be needed anyhow.


Trevor,

The Sentra rotor is a 4x100mm pattern, and when placed over the minilites I bought (from Moss, I believe), the holes line up. I think that the wheel, like many aluminum wheels, is centered by the countersink in the stud holes and the corresponding taper on the lug nuts. But maybe that's incorrect.

Now, the stud holes on the rotor are larger than the wheel studs themselves. This would appear to be the same rotor that OlPhartz uses (though I don't know that for certain, as they're loathe to reveal part numbers). On the assumption that this is true, I suppose that centering may be accomplished by a very close fit on the center hole, which has a bezel on the half-shaft side. As I say, I have yet to pull the shoes and wheel cylinder to see if the bezel accommodates the half-shaft's bulge. It is going to be *very* close, either way (can't quite get a good measurement inside the rotor 'hat.') If it does, and the fit is snug, I suppose it should be easy to spin the axle and measure rotor runout on the car.

However, let's assume that doesn't work. It seems to me that there are two options, but perhaps you are thinking of others.

First, one could expand the diameter of the bezel just enough so that the rotor did fit closely onto the half-shaft bulge, becoming 'self-centering' if you will. (The other side of the equation, applying coarse sandpaper or other abrasive surface to a slowly spinning half-shaft, seems a bit frightening, but could yield the same, incremental reduction--all that's needed, I suspect.)

In the alternative, the rotor would need two operations, as you seem to suggest: (1) re-drill for 4x4" bolt pattern (101.6mm) but with holes to fit the studs' diameter; and (2) open up the center bore sufficiently to allow ample clearance for the half-shaft, the bezel having been rendered useless.

As for OlPhartz, I have no intention of competing with that kit, which is very nicely done. I respect their work and the thought that went into the kit (as you can well imagine from my fumbling.) My purpose is to help out a different demographic by facilitating a DIY conversion for those who can't afford $1,200 or who like to tinker and don't mind some minor fabrication--the cut-off being welding, in my case. A trip to the local machine shop is not a put-off for most on this site, it seems, so long as it isn't prohibitive in cost.

If I were OlPhartz, I'd market the CNC brackets as an alternative to the full kit, as I think they'd gain in volume what they seem intent to wring out of margin in full kits. They and Frontline (and the handful of others offering kits) don't do that, so here we are.

That said, aside from the cost of machining in option two above, which I'll confirm with a visit to the local machine shop this week, are there other hidden costs that you think I haven't anticipated? I really don't want to design a solution that ends up requiring excessive machining, etc., which at some point would indeed make a complete kit a better option for anyone without a lathe (which describes most of us, I dare say).

Joel.
JM Young

You're choice of calipers may necessitate a proportioning valve. Of course, you also have to make new brake lines. I prefer locating the disc rotor with proper wheel stud holes and the counter sunk locating holes. This could be done by hand with a drill press and methodical measuring and marking, but would be much easier by a machinist using CNC.

I do not know what sort of product liability insurance OlPhartz has, but selling something as a complete kit helps reduce "user error" and tech support issues.

I'm all for a "home brew kit" and will help out however I can. Making small levers and such out of steel is not difficult even if you are just working with a hack saw and hand drill.
Trevor Jessie

Forgot to mention ... you can also order rotors drill to the PCD of your choice, but then you are looking at significantly more money.
Trevor Jessie

PCD = (4 x 101.6mm) pattern

Something else to consider is the amount of volume the new calipers will require to brake properly...

If to large a volume of brake fluid is needed, then you will have (lite,) braking, if to the volume required is way less then the midget, you will be locking up the brakes



Prop
Prop and the Blackhole Midget

Opps... sorry trevor

I just saw where you raised that issue and would need a porportioning valve

Prop
Prop and the Blackhole Midget

FYI...

The front to rear balance ratio is 90/10 for the midget. NOT 70/30 like most cars

What might be an easier solution, and an Idea ive have had for several years for rear disc brakes, but im not persueing because im converting to a mazda rx7 rear end set up....

Gut out rear braking componets, then modify the brake drum to take a motor cycle brake disc...aka weld in some extra metal blubs at 5 spots, then drill and tap them

the motor cycle disc seem to be screwed on at 5 spots, in a star configuration, from what ive seen in mall parking lots),

then just use some large heavy duty (4in x 4in x 3/8in and maybe 3in long ) angle iron as brakets and weld those to the axle casing and mount your calipers to it...and whola your done.

Exactly how important is the E brake... for me its a non issue, I always use a bright painted colored pet rock as a wheel chualk, and if possiable turn my wheel so im pressed into the curb, id think for the how brew DIY, they wont care that much one way or the other about an E brake

Anyway, that was my thought on how I would have done it.

Prop

If you woul
Prop and the Blackhole Midget

PCD = (4 x 101.6mm) pattern

Something else to consider is the amount of volume the new calipers will require to brake properly...

If to large a volume of brake fluid is needed, then you will have (lite,) braking, if to the volume required is way less then the midget, you will be locking up the brakes

Btw... the front to rear balance ratio 90/10 for the midget.

What might be an easier solution, and one I have had for several years....

Gut out rear braking componets, then modify brake drum to take a motor cycle brake disc ( they seem to be screwed at 5 spots, in a star configuration, from what ive seen in mall parking lots), then just use some large heavy duty angle iron as brakets and weld those to the axle casing and mount your calipers

Exactly how important is the E brake... for me its a non issue, I always use a bright painted colored pet rock as a wheel chualk, and if possiable turn my wheel so im pressed into the curb, id think for the how brew DIY, they wont care that much one way or the other about an E brake

Anyway, that was my thought on how I would have done it.

Prop
Prop and the Blackhole Midget

Trevor,

You and Prop are right to worry about a proportioning valve, and naturally I'd planned to test the setup *vigorously* before posting it as a sorted solution. That's the fun part, and one reason NM's near-vacant back roads (and maybe Kentucky's?) are nice. OlPhartz appears to use identical calipers, albeit with a lever that has a hole for a clevis pin sticking up at 12 o'clock instead of 9, so maybe we'll get lucky re: fore-aft balance. Those pistons are *tiny,* if you ever get a chance to check one out.

Thank you for straightening me out on the correct centering method. On that front, and provided the bezel in the Sentra rotor slips over the half-shaft bulge (I will try to find out this weekend, as the fiancé's mom is dropping by and I'll be able to steal some time), two possibilities come to mind.

One is an actual-size, PDF template (exported from a CAD program?) that users could print out and use to drill their rotors on a home-sized drill press. Mine was from Harbor Freight on one of their near-constant sales. It was cheap and is very competent. The template could be placed precisely by lining up representations of the existing 4x100mm holes and the center bore. That would limit the DIY setup to those with a drill press, of course.

Two is producing three CNC bits (or G-code that people could use to cut them): the caliper brackets; and a drilling template with a raised cylindrical part that dropped into the center bore. I don't know what a minimum run would be to make a handful of either one or both parts, but I've heard it isn't awful.

I agree on the levers. We could also provide a print-out template or diagram for making them. The profile needed is extremely simple and doesn't even require bending. I think the only challenge would be the rectangular hole that fits over the base of the parking brake shaft--at least I assume they're slotted in that fashion.


Prop,

Your notion sounds very innovative, but far too much fabrication for the likes of me. I was hoping to figure out something that minimizes the amount of fabrication people have to do--and welding in particular, in my case. I guess it's arbitrary, but welding is something I figure a lot fewer people know how to do than, say, drilling and cutting a piece of aluminum or mild steel to make a little bracket.

A parking brake is a must for me. I also like the idea of retaining functionality wherever possible. But that's just me.

Joel.
JM Young

Prop, how do you make out 90:10?
Paul Walbran

Square holes for the levers are easy with a drill bit and small triangular file

I do not think a paper template would work for drilling the rotors. It would be better to have instructions on how to lay out, mark, and drill the holes. Given a step by step instructions would allow someone to do a good job using a scribe, quality, straight edge, and divider (and of course the correct drill bits)

Trevor Jessie

I came across the 90/10 several years back when I was upgrading my tilton master brake and clutch set up ...I dont know the source anymore, but struck me as odd and in practice seems true as my proportioning valve is very extended to get good hard controled braking

Joel,

I certianly wouldnt me or other amatures doing the welding on my idea, for something this crucial, id want a pro welder doing the deed, and really from what we have talked about, it seems most of us would need to sub some portion of this out,

Something id give more thought to, is what is the type of person that will do this to there car, and why would they do it, once you understsnd that then I think you begin to understand what tools and shop experiance this type of person would have

To do this, is not going to be done with a screw driver, a vise grip a garden rock. Its going to take some creativity, some specialty tools, some real grit for risk taking.

I think trevor said it best, (paraphrasing) design the compont to work 1st then worry about how to machine the part, id say that also works for the human factor, design the part 1st then lastly deal with the human capability...some will find this daunting and sub the entire thing out, others willaugh and howl ""amatures" then proceed to completely modify your finished design into there own concauction and spend an hour to accomplish in there 75,000 sq ft shop with ever tool imaginable

I think you cant consider what the skill level is for this project, otherwise you will be just chasing your tail, id focas on who and why this type of person is that will want to make this upgrade

Not sure that made scence.
Prop and the Blackhole Midget

Correct me if I'm wrong, but doesn't the front/rear brake bias depend on the weight distribution of the car as well as the spring and dampener rates?
Trevor Jessie

Oh... please dont defame harbor fright, for midwest reneck hill billys and okeys, this place is church and is definatly more hallowed ground, then jesus could have ever created.

Haha

Prop
Prop and the Blackhole Midget

Trevor,

I hope so, because Thats my understanding and factory spec is 90/10 perhaps that changes with the additional wieght of added cup holders, and picnick baskets on the rear boot lid.

Prop
Prop and the Blackhole Midget

When I adjusted my tilton set up, I used a very technical well thought out and very procise approach ....I wound the proportioning bar down to the extreme end then proceeded to do several high speed approaches on a straight streatch of road in front of my house and slamming on the brakes ... I did this approach several times untill my underware just felt natural. I found that wearing a white doctors lab coat and a clip board , didnt improve the results, but god, I sure looked cool with the added appearce to the neighbors that I looked like I knew what I was doing....

I love engineering, if it was something that only a few knew how to do, id have become one.

I say the above as a joke to emphise the importance of not getting to overly involved with the braking ratio... I sort of lost my way doing this and in the end found its really just seat of the pants that will.solve the math equation the best, unless your just educated.and have the 1/2 million dollars worth of test equipment. And the 8 years of collage

Prop
Prop and the Blackhole Midget

When I adjusted my tilton set up, I used a very technical well thought out and very procise approach ....I wound the proportioning bar down to the extreme end then proceeded to do several high speed approaches on a straight streatch of road in front of my house and slamming on the brakes ... I did this approach several times untill my underware just felt natural. I found that wearing a white doctors lab coat and a clip board , didnt improve the results, but god, I sure looked cool with the added appearce to the neighbors that I looked like I knew what I was doing....

I love engineering, if it was something that only a few knew how to do, id have become one.
Prop and the Blackhole Midget

Hi Joel,
If you can send me a sketch of your design i will get it drawn up for you and give you a copy in a number of different formats.

You would then be able to send it to any machine shop/laser cutting service and they would convert the file to match their machines.

Can't help with the design unfortunately as my axle is non standard.

I recently did a rear brake conversion using 8" drum brakes from a mitsubishi lancer, it went ok and the brakes overall are improved (but that i expect is mainly because their not full of oil anymore!)but i'm still fiddling with the handbrake.

Remember it's never as easy as you first think.... and allow at least double the time you expect for the project...

See my thread:
http://www.mg-cars.net/mg-midget-sprite-technical-bbs/rear-end-troubles-and-rebuild-2014051708442231277.htm

Andy Phillips (frankenfrog)

Trevor,

Cool - I hadn't thought of using a little triangle file, which I got in a set a long time ago and never figured out a use for. Very nice.

Sounds good on the drilling methodology. I will, as it turns out, have time to remove the rear shoes and cylinder from one side Saturday morning, as the girls are going to the International Balloon Fiesta for the crack-of-dawn launch (I've seen it too many times to care). I will let you know if we get lucky with the center bore slipping over the half-shaft bulge. It is going to be a c-l-o-s-e call.

It's kind of suspenseful. I don't think I've looked forward to waking up this early on a Saturday morning since I was a kid watching the Road Runner outsmart Wiley E. Coyote.


Prop,

Well, I had just planned to just go like heck, stomp on the brakes, and see if the rear discs lock up. If so, put in a valve, turn the knob, rinse, repeat, etc. I *do* enjoy trying to figure stuff out in advance, and I'm with you on the engineering as a once-and-future career. However, I'm too old for yet another degree program, and the seat of my pants just ain't that accurate. You've got the advantage there, I'm afraid...

Joel
JM Young

Im probably not much younger then you... im pushing 50 in a few months...im not sure how that happened

Prop
Prop and the Blackhole Midget

Prop,

I suppose you're right that it's nigh on impossible to predict what skills and tools (which don't necessarily correlate) that people may have. That said, I do believe it is consistent with both my intentions and a sort of built-in aspect of the engineering challenge to design a DIY solution that describes the shortest straight line to the desired result. Put another way, a solution that requires the smallest number of specialized tools and skills reflects good engineering--at least from one point of view.

Trevor's elegantly simple suggestion for how to achieve a rectangular hole in the brake lever is a good example. By pointing me to a cheap tool I've long had, which anyone can afford and use without special skills, and whose application during the brief learning curve during won't endanger an expensive component, he transformed a near-perfect caliper into perfect for our purposes. The brake lever steps in our instructions will now read something like:

Select stock by [x] width and [y] thickness (at any Lowes, Home Depot, Metal Mart, et al.)
Drill hole for clevis pin
Drill & file 2nd hole to fit parking brake shaft
Cut to length
Round corners if desired and break edges.

That's the sort of light fabrication task that few will mind, and many will find fun and satisfying.

As for the more existential query in your last email, I believe Richie Havens famously provided one answer, with his classic song, "Younger Men Grow Older." You can listen to it here: https://www.youtube.com/watch?v=HlIvLpctCr8

As for my actual age, which you seem to ask by implication, all I'm admitting is that the photo on my Amazon 'author' page just *might* be from a few years back. I blame the editor, whom I parodied in the novel (with full justification).


Andy,

Sorry - didn't notice your post nestled in between the others. Tired eyes, I guess, as things have been crazy stressful at work lately.

I greatly appreciate your generous offer, but I think Trevor has already volunteered to do the CAD/CNC-related end. That said, please do keep the offer open, just in case Trevor gets hit by a bus, bass boat, wayward Citroen, or whatever the mechanized hazards are in the Blue Hills of Kentucky. Here in NM, it's the F350 Super Duty-driving redneck cattle ranchers, who seem curious to find out if my Midget will fit under their front differentials.

Joel.
JM Young

So, I have learned that there are two categories of brake cable levers. Since I only know how to post one picture at a time, here is the first type, from a Maxima caliper, I believe. It's # 4 in this image.

JM Young

Now, the above type is what I supposed all of these calipers have, and which would lend itself to a simple fabrication as Trevor suggested, using a drill and triangular file.

The second type, which unfortunately *might* be what is on the Sentra caliper, looks like the image attached to this post. It's # 21, and looks as if the shaft is an integral part of the lever. I certainly hope this last diagram, which is posted on Autozone's website, is not right. I am going to check it out. If so, there are a couple of other candidates that would fit this rotor, like the caliper from the '92 Acura Integra. Though I'll have to look into that style of lever as well.

Joel.

JM Young

...and we're in luck. The attached diagram indicates that the 1992-96 Acura Integra caliper (slightly different , but not much through that year spread) has a lever which is stamped steel, attached to a cam bolt, and which presumably utilizes a square 'keyed' hole (had to tell in this diagram). It also has a hole that would accommodate a clevis pin.

The pads *appeared* close to the same width in a radial dimension as the Sentra's pads last weekend, though I didn't have calipers or measuring tape with me when I stooped down to look. All I had was a piece of mechanic's wire to measure the bedding surface of the Acura rotor, which ended up pretty close to the Sentra rotor.

I am going to take vernier calipers to accurately measure the size of the pads and bedding surface at the pull-n-pay Saturday morning, and if things look good, grab the Acura calipers with mounting brackets and remove a lever to make sure Autozone's diagram is correct.

If so, then these calipers should work great--and I suppose it's at least possible that the hole is square instead of rectangular, in which case the lever could simply be rotated 90 or 180 deg. to get in the right orientation for a yank from the parking brake rods. After a little fiddling with the spring, that would do it.

These calipers have an extremely short brake lever pull (only a few millimeters when I pushed on them), which should yield a very serviceable adjustment on the Spridget hand brake.

We'll see...

JM Young

Don't let the e-brake lever dictate too much. There are ways to easily make adaptations for something that has a basic operation.
Trevor Jessie

If I was going to file a round hole square I would chose a square file rather than a triangular file.
David Billington

I agree David, but for whatever reason more people have a triangular file in their tool box.
Trevor Jessie

Instead of CNC, the brackets could be cut with waterjet, much cheaper I think as it's a 2d cut only
Alex G Matla

Joel,

Its looking just way to complex for me, can you try complete redo and make it more simpler.

:-)

Prop
Prop and the Blackhole Midget

Trevor,

Okay, fair enough. Thanks.

Turns out that all the Acura Integra pads from '87 to '96 have slightly different backing plate profiles--so have to be used with their corresponding calipers. However, they all have the same curved profile and measurements: 29mm x 69mm. So, the pads should fit nicely on the Sentra rotors' bedding surface, which I measured inaccurately the first time. That surface is actually 31mm wide, not 32mm. The Integra rotors are 239mm, versus the Sentra's 234mm, but I'm hoping that radius difference isn't enough to ruin the fit.

Of that year range, the '95-96 models have the brake hose angled away from the hub and toward the differential, much like the Sentra calipers (see attached image). The earlier models have it angled 90 deg. from the axle, which would be fine if it directed the hose up over the axle tube. But I think I like this configuration best. There are three Integras in this year range in the pull-n-pay nearby, so I'm going to grab a pair Saturday and monkey around with the levers. I'll also try and do the rotor test fit.

These calipers really do have teensy pistons, so the bias shouldn't be too terribly far off. At any rate, Wilwood has a basic proportioning valve that's pretty nice, which you can get with either metric or sea threads: http://www.summitracing.com/parts/wil-260-10922/overview/


Alex,

I guess you could be right on the water jet cost; I am ignorant of the differences. But there may be a need for a spacer function, which would require varying thickness between the circular or 'J' shaped mounting flange and the tabs for the caliper bracket. Seems like CNC would be the way to go if that's true. I think Frontline welds on their tab spacers (unless I'm looking at the picture wrong), and I'd prefer a one-step manufacturing process.


Prop,

I think you're going to enjoy the setup, though I understand you may be installing an entirely different rear end with its own discs anyway.

Joel.

JM Young

Joel,

I know I will enjoy the outcome, I was just giving you a tease...

Have a good and productive weekend

Prop
Prop and the Blackhole Midget

Prop, going back to your 90:10 thing, I'm really dubious about it. The area ratio between front 2" caliper pistons and the 3/4" rear wheel cylinders is 7.14:1, which in percentage terms is 88:12. However it's not as simple as that as disc brakes lack the servo action of the leading shoe in a drum brake set up. This is highly effective and will increase the effort on the rear brakes subtantially. My bet is that it brings it up to the more normal 70:30 - especially when you consider the Mk1 with all-round drums were approximately 2:1
Paul Walbran

Prop,

I kind of thought so, but thanks for reassuring me. I guess I deserve what I get after ribbing Trevor about bass boat hazards.

I am really excited about designing a conversion that is elegantly simple. I have borrowed a '96 Nissan Sentra caliper from Autozone--my original choice, you may recall--and tomorrow will confirm whether it's lever is brazed onto the cam shaft that actuates the parking brake. If so, I'm going for the '96 Acura calipers, as with their flat plate with cam bolt system, all I have to do is drill, file, and cut to produce a lever, as we've been discussing. I hear you and Trevor about not worrying too much about this, but I really do want a solution that's well within my skill and tool sets.

Trevor,

I note in this regard that the flange originally used for the cable brace on the Acura caliper would make for a nice, alternative anchor for the new spring (or creative use of the existing spring). You can see the flange in the image attached to this post.

The left-hand view in this image also suggests that the new lever might be a 45 deg. dogleg or modified 'Z' profile, with one part longer than the other, thus potentially putting the end with the hole to receive the clevis pin *exactly* where the OEM brake rod ends up. All you'd have to do is rotate the caliper around the axle until the angle of the lever aligned with the open end of the OEM brake rod--at least I think it's possible to do that without fouling the left spring...?

Now, *that* would be keen--to be able to simply bolt on the CNC brackets, slip on the rotors, bolt on the calipers, attach the OEM rods and new hoses, bleed and go.

Paul,

The pistons on these '96 Acura calipers are quite small. Assuming the curve of the Acura pads won't cause them to hang off the Sentra rotors as I mentioned above, I will bring a pair home and post measurements of the pistons. Perhaps we could then figure the volume and percentage front-to-rear (my math skills are lousy), and compare to the stock Spridget setup.

I smell NM grass-fed steaks on the grill. Over and out.

Joel.

JM Young

Joel,

Im very impressed with the work you have already done, even if it fails your already (doulbtful) your research skills are 2nd to none and id bet on you on any future projects.

Paul,

I simply cant argue with you on this one, I wish I could....I no longer have the source to back up my claim of 90:10, and your a very acomplished engineer who I have a lot of respect for.

I do belive that it is 90:10, but I cant back up that claim mathmatically or by source name

But if I do find an angle, ill be back.

Thanks for the challange... I wish I could have been a better competitor.

(Not that im conciding) :-)



Prop
Prop and the Blackhole Midget

Gentlemen,

I am confused by something. If you look at the yellow car in this gallery for OlPhartz, http://www.olphartz.com/gallery.html, and zoom in, it appears that they used the existing stud holes on whatever rotor that is. The owner has painted the 'hat' and the narrow band that separates its circumference from the bedding surface in that photo. You can verify this by looking at the photo of the wire wheel installation, where the hat is not painted. But, point is, if they had redrilled, there would be two sets of holes, correct?

So, there has *got* to be another rotor out there with the correct PCD that would eliminate the need for redrilling. I mean, what would an alternative explanation be?

One related observation is that there is substantial slop around the OEM Spridget studs in the holes of the Sentra rotor (I would send a photo but haven't learned how to shrink down an image from my iPhone). I guess one possibility is that they pressed slightly fatter studs into the hub, which would produce a tighter fit in the Sentra rotor's holes. But wouldn't they then be a skosh off, due to the 4x101.6mm OEM pattern?

I'm starting to think I need to revisit the exhaustive, non-application specific listing of rotors on Autozone' s site, as perhaps I was reflexively eliminating other-than-4x100mm configurations as I breezed through. Might be one in there has the right overall diameter, but with the 4x101.6 PCD and smaller stud holes. It might just need the center bore opened up a bit, as I think the center bore size was another eliminating criteria I was using.

But, at any rate, I'm thinking I need to do more research on rotor options before plowing forward. The animal clearly exists. I just have to find out where the bugger is. Perhaps it's a European or Japanese market-specific car, which might explain the more slender studs.

Joel.
JM Young

Here is a listing of rotors by dimensions, and later by application: http://www.autopartsource.com/catalog/2310_rev_A.pdf

I cannot find *any* with a 4x101.6mm PCD. There are tons of 4x100mm, and several 104mm, which is 4.094". But nada with 4x101.6mm PCD. Hmmm...
JM Young

Joel,

It looks to me from that photo that the studs are not central in the holes so that indicates either a 100mm PCD or possibly FIAT group at 98mm PCD. Many cars these days use M12 bolts so with 3/8" studs you potentially have about 2.5mm to play with so a 100mm PCD with 12mm holes would go straight over, a 98mm PCD might if the holes have sufficient clearance on the bolts.
David Billington

Yeah, clearly, I should have perused front rotors as well. In starting to look at these applications, I quickly found (for instance) a 1981 Honda Civil front rotor that is 8.5" or 215mm, with a 4x100mm PCD. I'm thinking there is likely a solid rotor of the right size and *perhaps* with the right PCD that is a front rotor.

Sheesh, do I feel silly for not looking at front rotors. Back to the books...

I still think, however, that the calipers I'm looking at are a good alternative to whatever OlPhartz is using. I really like the idea of easy-peasy, DIY brake levers that reach precisely to where the OEM brake rods end up.

Sorry for the delay, but if there's a rotor that will simply drop on, or which merely needs the center bore opened up a little--which isn't going to cost more than a few dollars at the local machine shop--it only makes sense to find it! Of course, if it's like this one, and the width of the bedding surface is wider than the narrow Sentra strip, I *could* use the 240SX calipers after all!

Bottom line is, there's more research to be done before making my prototype mounting bracket!
JM Young

It would be possible to use a slightly different PCD like 4x100mm, but you still need the location of the rotor via the countersunk screws. Personally, I'd want the the proper PCD AND the countersunk screws.

Trevor Jessie

On the good news front!

I popped off the spring, removed the nut and lock washer on the Sentra caliper, and... voila! These calipers DO have a removable, stamped steel brake lever. Autozone's repair diagram was wrong. So, it's a snap to make a lever that would work. That means, the redrilling and center bore issues aside, the Sentra rotor and caliper setup will work fine.

Only questions, assuming I can't find a rotor with the PCD already spot-on, are: (1) whether the Sentra rotor's center bore will clear the Spridget half-shaft bulge (we'll know after breakfast), leaving only a re-drill for stud holes; and (2) whether the Acura caliper yields a more advantageous location for the brake lever than does the Sentra caliper, as I am now wanting to use OEM brake rods if at all possible.

I need to have a cup of coffee and figure the last issue out. For some reason, it seems to me that the Integra caliper might possibly allow placement of the end of a lever closer to where the end of the OEM brake rode ends up, but I need to hold each of them up to the axle and figure that out. This is the fun part, unlike poring over endless rotor specs...

Joel.
JM Young

Good Afternoon,

Have you got anyone to CNC machine the brackets yet ?

Best regards ,

Chris
C H Buckenham

Hi, Chris.

I believe Trevor has offered to do that, and now is waiting for me to figure out which rotors and calipers will work best.

I think I just figured out that, indeed, the Integra calipers allow a bit more flexibility in establishing a profile for the lever that may meet the end of the OEM brake rod without shortening it...

...and, here's an interesting thought. I wonder whether the original lever on the OEM drum brake setup might work, #75 in the Moss diagram: http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29305#top

I am talking about the dog-legged piece, which would be separated from the internal piece that goes between the shoes, then drilled and slotted as discussed above to fit the rectangular, keyed portion on the caliper cam. Experimenting with putting the square cam hole at various locations relative to the elbow would produce a pretty good range of positions for the existing hole that receives the clevis pin.

Now, that would be just too good to be true, but I think I'll fiddle around a bit and see what's what.

Joel.
JM Young

David,

Thank you--and sorry that I didn't respond to your post. I think you're right, but I thought perhaps my eyes were playing tricks on me, or there were weird shadows, etc. At any rate, I gained a bit more confidence after reading what you wrote, got creative, and... ...success!

I pulled a half-shaft to see if the Sentra rotor would fit, and it was so tantalizingly close that I flipped the rotor over, dropped it in the vise (6" jaws) hat down, and ran a dremel around the inner bore with the cylindrical reddish stone it came with. I alternated that method with resting the dremel motor against the inner shoulder of the hat and turning the rotor to try and approximate the chamfer--being careful not leave the stone idling or gouge the steel each time I reengaged the stone. After a little while... voila! The rotor slipped snugly into place.

The first rotor had roughly .002" of slop on the half-shaft bulge, enough to hear it 'clink' when pushed sharply, but hard to see with the naked eye (at least an old eye like mine). So, I did the second one the same way, but the second time the slop is just .001". Each took about 30 minutes, but I was going slowly, so as not to over-enlarge the bores or gouge the steel when doing the chamfer. The vertical part of the bore was much less touchy.

In short, as I wondered earlier in this string, carefully opening up the 68mm bore on these 234mm (9.2"), $13 rotors makes them 'self-centering,' and the holes end up inside the stud holes on the half shaft. Of course, the latter, 4x4" holes range toward the outer edge of the slightly larger holes in drilled into the rotor at 4x100mm PCD.

That said, with the rotor snug on the half-shaft bulge and clamped between the half-shaft and the minilite @ 80 ft. lbs x 4 studs, I would imagine things should be quite secure. I don't think that the .002" of runout will cause any problems, but I guess we'll find out. Any thoughts on that issue?

*Note: the thickness of the rotor's hat is just a few hundredths thicker than the OEM drum's mounting surface, so the Spridget's track will grow ever so slightly. But I don't think it will be enough to cause the tires to rub on my square-fender '67.


Trevor,

I actually like your belt-and-suspenders approach. I know that I haven't gotten the rotors redrilled as you suggest, but it seems like they'll be fairly secure when sandwiched by the wheels. Also, it wouldn't be too hard to drill for a countersunk locating screw, right?

I guess that I don't understand well enough the kinds of force that will be placed on the rotors to demand the redrilling, despite that they're anchored quite solidly on the 70mm center bulge. Wouldn't it be primarily twisting from the caliper, which would transfer into shear force on the edges of the studs in either scenario? Perhaps there's another kind of force generated by rotors that worries you, and which I don't understand. If so, please fill me in. I am not an engineer.

Mañana, I am going to pick up some Integra calipers from the pull-n-pay. I will also try to post a YouTube video of my simple but accurate method of opening the bore, and link to it in the next post. I suppose people could do the same thing with a drill motor if they lacked a dremel, but the latter are a little easier to control and might be a touch faster with the high rpms. Doing two rotors didn't faze that little reddish stone.

I assume the best way to begin mocking up the mounting bracket is with a cardboard cutout to get the 2D close, then begin the wood or MDF 3D model, from which we'd take measurements to inform your CAD/G-code work. Is that what you had in mind? Please help me with the proper steps in this regard, as I've never participated in this kind of design work before.

Joel.
JM Young

My concern about using incorrect PCD has nothing to do with sudden failure, but rather the possibility of an annoying imbalance. Granted the rotor's mass is close to the center of rotation, so it might not make any difference. Drilling a counter sunk hole would be fairly easy, it could be located by first installing a stud in that hole that had been turned down to a point, then place the rotor on an tap it with a hammer to center mark the hole.
Trevor Jessie

Trevor,

Thanks for clearing that up--that's a big relief. The last thing I want to do is come up with an 'elegantly simple solution' that makes a Bugeye hop around like a frog just before the wheels fall off. That said, the dremel-machining method does seem to produce accurate centering, though I suppose somebody could mess it up if they didn't keep the stone moving.

Cool - I will do as you suggest, and add the locator screw steps to the DIY instructions.

A few items for discussion:

First, the photo of the yellow car I discussed above shows an installation on a Bugeye, and the caliper appears to be toward the front. I am working on a leaf spring Spridget, and wonder if you mind if we limit ourselves to the latter for now. I don't know of anyone in Albuquerque who has a Bugeye.

Second, assuming you like the cardboard template method of determining the shape of the bracket, do you have any suggestions about the outside profile? I was thinking of approximating something like the basic shape shown on the TR6 page, http://www.britishv8.org/Articles/TR6-Rear-Disc-Brakes.htm but with whatever differences are dictated by the Integra calipers, Spridget axle housing, and leaf spring clearance/braking rod issues and anything else you can think of that would affect placement.

I guess my chief concern apart from aesthetics, which I suppose you can clean up on the CAD software, is how much thickness to leave outboard of the four attachment holes and two caliper mounting holes, and whether to have 'ears' rather than a straight line or concave arc between the caliper mounting holes. What would you suggest?

Third, my original plan was to hand-make a pair out of 6061 after I send you the plywood or MDF models, just so I could get my car back on the road. However, I'd rather have a pair of lovely CNC-made brackets. What do you suppose your turnaround time would be to produce the G-code? I don't want you to feel at all pressured, but am naturally eager to be able to drive the Midget with four-wheel discs.

Joel
JM Young

Your correct about the pcd being dead on, when I mmodified my hurricane wheels I had to account for a sloppy pcd, by having a centering rings made...even though the spec seemed negligible

That $1200 for the kit is starting to look pretty economical ...hahaha

Prop
Prop and the Blackhole Midget

I'll offer other thoughts when I'm back at my computer, but drawing the parts in a cad program is easy. I can make the gcode for my machine, but other shops would need to generate fot their own machines. However, I can take your mock ups and cut the parts and verify they fit. Then you can install everything and see what tweeks are needed. I'll cut them for the cost of the material plus a few bucks for some fresh cutting oil.
Trevor Jessie

Trevor,

That is very generous - thank you. Whenever we figure out the needed thickness of the stock, I will buy enough for two sets.

Guess what? I just test fit the calipers and held up the OEM drum brake lever, and will post some photos shortly. There is loads of clearance for the caliper, and the arc of the OEM drum brake lever is almost exactly what we need, but it will end up an inch or two short of where it needs to be--down in the minilite's dish a little bit.

Point is, this setup will almost certainly be able to use the OEM brake rods and clevis pins. Pretty neat.

Joel.
JM Young

Here come some pictures from today.

First is the '96 Sentra rotor on the Spridget half-shaft after machining with dremel.

JM Young

Here are some stills of the machining. First, laying the dremel motor on the edge of the 'hat' and turning the rotor to reproduce the chamfer. Very easy and accurate.


JM Young

Now, enlarging the bore. This is even less touchy than making the chamfer, which requires gentle re-engagement with the metal while turning the rotor smoothly (I used a towel to allow rotation without skipping). This part is basically fool-proof. Just clamp the rotor and move the stone contrary to dremel's rotation.

JM Young

Here is the '94-96 Integra pad on the '96 Sentra rotor. Perfect fit.

JM Young

Here is a general view of the caliper positioned on the 9.2" 234mm rotor inside a 13" minilite.

JM Young

Loads of room between the caliper and wheel.

JM Young

Here is the Integra's keyed lever.

JM Young

Here I have marked the cam bolt profile at a likely spot on the Spridget brake lever, to put the clevis pin hole as near as possible to the rotor. Naturally, the second part of the drum setup would be removed.

JM Young

However, the lever isn't long enough to put the hole to receive the clevis pin where it normally ends up--about another 1~2" farther inside the wheel's dish.

JM Young

Outside profile? Are you asking about the outside shape of the adapter? I guess that depends on the amount of offset is needed between the two mounting surfaces. If much off set is required, you may want a beefier section for load transference. It might become obvious when you started trying your CAD (cardboard aided design) and your MDF mock up.

Do not worry about buying the aluminum stock. If I do not have the size needed I can get some from my supplier.
Trevor Jessie

Note that the profile of the Spridget lever will allow it to rest against the existing stop pin on the Integra caliper.

Two obvious solutions to the length issue. First, and easiest, merely cut the spridget brake rod, get turnbuckle and die with matching thread pitch to cut threads into the shortened rod, dial in the right length to put the clevis pin spot on, and lock down the affair with two nuts.

I really like this solution, because the turnbuckle would allow essentially infinite adjustment both for length and alignment of the brake rod's end. Also, one can simply drill another, small hole in the inner edge of the Spridget brake lever's 'dog-leg' to connect a regular spring to a bolt in one of the existing cable bracket holes, or perhaps the OEM Integra coil spring will clip onto a notch filed in the lever.

Second, if you prefer to leave the brake rods intact, you'll have to fabricate another, longer dog-leg lever. However, that would require fixing the location of the caliper around the rotor to align the lever with the clevis yoke. This might reduce the ability to position the caliper's bleeder valve as high as possible.

Anyway, pretty cool. Coming along nicely.
JM Young

Trevor,

Looks like our last posts missed each other in transit, somehow.

Yes, precisely, I was asking about the outside shape. Guess we'll see what develops. Sounds good on the aluminum supply. You'll probably get a better price than I could have, anyway.

I pulled a hub, removed the backing plate and wheel cylinder, and ran out of time. I will try and remount the hub, insert the half-shaft, mount the rotor and start my demi-CAD work. May have some questions for you as that progresses. I love your acronym for my end of the design work, by the way. Hilarious.

Joel.
JM Young

how many degrees of rotation is necessary for the ebrake lever?
Trevor Jessie

Trevor,

I don't yet know, but will post when I've had a chance to check it out.

I suppose if one had to remove the caliper to bleed the system, it wouldn't be a big deal. Two bolts and remove the brake lever's clevis pin. However, it would be nice to be able to bleed without disturbing any fasteners.

Joel.
JM Young

Trevor,

You know, another possibility that might allow use of the longer lever without having to rotate the caliper around the rotor to obtain the correct alignment occurred to me. I suppose that I could just put the lever in the vise and bend and/or twist the end of the lever to align it.

Anyway, we'll see what's what when I can grab some more time. May be later this week or even Saturday, but I hope not.

Joel
JM Young

Any chance you can do away with the rod and levers and just use a pulley (on a spring perhaps) and just use a steel cable in its place...id think that would give you loads of options

Another thought, what about a 2nd brake caliper to just perform the funtion of an E-Brake

Prop
Prop and the Blackhole Midget

Prop,

Any chance that 'Prop' is your nom de plume, and your real name is Rube Goldberg?

Seriously, though, a second caliper would increase the unsprung weight even more (the caliper and rotor probably outweigh the drum setup), and I really don't see the parking brake as a problem. As I've said above, it's either a longer lever fashioned properly, or cut-and-thread the existing brake rod to fit a shorter lever that may well be made from the OEM Spridget drum lever. Really not that difficult.

Joel.
JM Young

Trevor,

If this isn't the easiest DIY project I've attempted, it certainly is a runner up. Here is the setup in place. The shiny bit between the caliper and wheel is a spanner shoved in there to keep the caliper from falling out against the wheel. But, obviously, there is a ton of clearance laterally for the caliper.

Here come the pictures, which show that this should be straightforward.

JM Young

Here is the rotor in place. Zero discernible runout after clamping a straight edge against the leaf spring and rotating the hub.

JM Young

In answer to Trevor's query about how much we'd have to rotate the caliper around the disc to obtain the correct angle for the brake rod end... how about zero degrees? It isn't close; it's perfect when the caliper is positioned in the identical orientation as to how it sat on the Integra from the factory. That means, the bleeder is topmost--you can see it extending aft just below and behind the top 'floating' bracket mounting bolt in this picture.

JM Young

**Note that in the above picture, the rod is sitting forward of the cam bolt, whereas in service it will sit aft and inboard of the bleeder valve that appears to angle toward the centerline of the leaf spring in this shot.

Trevor, that means we'll indeed be able to use the OEM Spridget 'dog leg' brake lever detached from its other component (that spans the shoes), but will just have to shorten the brake rod. This will enable very precise adjustment, and since the pull is extremely short on this calipers, the Spridget's parking brake should be at least as few clicks as it normally is.
JM Young

Trevor,

In this shot, you can see where the brake rod will actually end up--aft of the cam bolt, which is correct given its clockwise rotation. You can envision the dog leg OEM Spridget brake rod sitting as I had it in an earlier photo, above.

It's possible that we could use a longer lever, but it looks like the end would put the clevis pin almost against the body of the caliper. So, using the OEM Spridget piece and doing the turnbuckle two-step is probably easiest.

JM Young

Trevor,

In this shot and the above, brake rod picture, you can see that we may not even need a step machined into the adapter, which OlPhartz needed to use the Sentra caliper. I had some 11mm maple stock laying around, and although I couldn't fire up the planer without waking the neighborhood at 5:30 a.m., it looks like we could use a flat adapter, assuming you believe 10mm 6061 would be strong enough.

If you wanted a bit more meat around the mounting ears, we could use thicker stock, and all you'd have to do is mill down the area that encircles the axle flange.

JM Young

Did I say "perfect"? Actually, as you can see here, my vision under the car with my head cranked around wasn't spot-on. That said, it would be simple to place the lever in the vise and tap it with the ball peen hammer to get the few degrees exactly right.

You can also see more clearly in this picture that using a longer lever would either foul the bleeder valve, or at minimum interfere with easy bleeding. Since the caliper ends up in precisely the same orientation as stock, I'd like to keep maintenance dead simple, too.

JM Young

Here is the rotor with caliper placed in the identical orientation as on the Integra. In the previous photo, you can see that I had slipped a shock busing in between the caliper body and leaf spring, so there will be just over an inch clearance between the caliper and leaf spring in service. Ample, I would think, to allow removal and servicing of the caliper if needed.

JM Young

Trevor,

Unless you tell me otherwise, I am going to go ahead and make a 10mm adapter out of wood (I think I'd rather use hardwood over MDF, as that way I can mill it without dulling my planer's blades). Please advise as to whether you'd like me to laminate another layer onto the tab into which I'll drill holes for the Integra caliper mounting bracket's bolts. If so, please give me a sense of how much extra thickness you think there should be in that area.

I have family coming into town Saturday, but should be able to make the prototype bracket Sunday. I assume you don't need me to make both sides, as presumably it is easy to create a 'mirror image' adapter for the left side in your CAD program. Please advise on that issue as well.

Joel.

JM Young

Okay - I need more coffee, clearly. I said above that the cam rotates clockwise, but you can see from the holes for the cable-stop bracket that I'm wrong. The OEM Spridget brake rod, attached to the Spridget dog leg lever, would end up *forward* of the cam bolt, as I had it in the first of the related photos above.

That means, a longer lever would *not* foul the bleeder or get in the way of regular maintenance. It would, however, come perilously close to our new adapter. So, pardon my bleary-eyed excitement, and I'll resolve whether we can use a longer dog leg or will have to shorten the OEM brake rod after I get the thing bolted up on Sunday.

Bottom line, though, is this conversion is dead simple. I assume the only task left will be to cut the original brake line, attach a fitting that will screw into the end of the Integra caliper hose, and bleed the system. With Integra hoses (even stainless steel jobs) and brake fluid, the parts cost of this conversion is going to be less than $250, if my sleepy-head math is right.
JM Young

So a 1 cm thick adapter centers the caliper?

I would start of with a thicker adapter and mill it off as needed (after a test fit) to get it centered. If you plane the hardwood, I would think that it would keep its shape until you have done the mock up. Then when you finish it, you can make your detailed measurements.

We might need an engineer to offer an opinion if the adapter is of sufficient strength once the initial design is done. My gut tells me that 1 cm would be sufficient so long as we do not make the tabs too thin.
Trevor Jessie

Also, my question about the e-brake degrees of rotation was more about if the travel of the stock system would be enough for the chosen calipers.
Trevor Jessie

Also, I haven't dug through the stock bin yet, but I know we have some 1/2"x 6" x 4' bar back there. I'm thinking that should be ample size... or will I need to find some wider bar/plate?
Trevor Jessie

Trevor,

So, on the thickness, it looks like the TR6 adapter lacks a thicker portion for caliper mounting tab and is just a flat plate, whereas other designers opt for a thicker tab. Frontline incorporated a welded tab, as opposed to CNC machining their adapter from a thicker billet: http://www.frontlinedevelopments.com/products/midget/reardiscbrakekit.shtml However, it looks to me like they did that primarily to center the caliper bracket over the rotor. Now, my choice of the Integra caliper ironically might create a plate that's too thin, as I laboriously went through literally hundreds of calipers before settling on one that, when paired with the Sentra rotor, would allow me to use a flat adapter plate. I've got the caliper bracket clamped to the rotor in the test-fit, so every fraction of a millimeter I move it away results in a thinner caliper. But a 'stepped' plate could possibly retain a cross-section in the gap that is actually thicker than 10mm. I'm just not good enough at visualization to work that out without actually building the mock-up.

Worst-case scenario is, I end up back with the Sentra calipers, which we know will work. OlPhartz uses a design just like Frontline's, in that the thicker portion is used to center the caliper, which has a longer 'reach' than the Integra caliper.

Assuming I didn't choose a caliper with too short of a reach, my sense is that virtually all of the force generated by braking is torsional, so I agree that a 10mm/1cm plate made of 6061 would probably be adequate. Since the hardened bolts that came with the Integra bracket get torqued pretty good, it isn't as if the entire twisting force is borne by the bolts as sheer, and the steel Integra bracket would not only spread a lot of that force across the whole tab; it would reinforce the aluminum once clamped against it against any tendency to twist away from the plane of the rotor.

On the width of the stock, I'm sorry that I won't know that until I make the wood mock-up, as with the thickness issue. But virtually all of the designs I have seen simply exceed the diameter of the flange by a few millimeters and make some aesthetic choices to set their adapter apart. One can't patent this method of mounting a caliper because there are no viable alternatives (basic intellectual property law), so making it look different or tailored to a particular rotor and/or caliper choice is about all people can do to 'brand' their part.

Speaking of the latter, please email me at the above address, as there are some issues I need to discuss that won't interest people following the tech developments.

Joel.
JM Young

10mm 6061 is what I have used for my conversions, it has been well up to the job. Note though that the adaptor is a fairly substantial all round, approx a 6" circle with lugs for the caliper.
Paul Walbran

OK, I'll email you. Truthfully, I'd rather machine it from plate rather than bar, so I'll probably pick up some 1/2 inch 6061.
Trevor Jessie

Trevor,

I just scoped out the thickness aspect, and will have to compare the Sentra caliper with the Integra in that regard. It looks like the Sentra calipers would present a similar quandary to what we face with the Integra calipers. That is, end up with a stepped adapter, which uses a 10mm main portion that bolts to the axle flange, and a thicker tab to affix the caliper.

Only question is whether the configuration of the Integra’s ‘floating’ bracket results in any excessively thin places in the ‘step’ area, which I suppose one could compare to the riser in a stair case, if that helps visualize things. Of course, here, the ‘riser’ portion is curved rather than straight.

***

So, that didn't take long! Indeed, the Integra caliper's floating bracket is taller (longer, if you're thinking radially outward from the axle), and would result in a 'riser' portion that would be too thin. Attached is a photo of the Integra bracket, and next I'll post the Sentra bracket.

Joel.

JM Young

...and here is the Sentra bracket. *Much* shorter, and having cranked my neck around inside the wheel well just now with the Integra caliper clamped in place and shimmed to center the bracket over the rotor, it is clear that what I said in my very first post was right, all along--using the Sentra rotor and caliper is the ticket!

The brake lever situation is going to turn out much the same.

So, Trevor, I'll make up the wood or MDF mock-up over the next week or so, after the family-visit blitz this weekend, and get it shipped out to you.

Joel.

JM Young

The century is at hand, will it make the 100 post?

Prop
Prop and the Blackhole Midget

Paul,

Sorry for the delayed response. Thanks for confirming the thickness of your adapter. Sounds like Trevor's gut reaction and my less-informed leanings were on target.

All,

It will be a while before I post again, as I've got much to do and a delay in getting some components. Thanks to everyone for their generous input to date.

Joel.
JM Young

Congrats joel,

100 posting for a topic is always great to see

Have a good time with your family...see you when you get back

Prop
Prop and the Blackhole Midget

Prop,

Thanks for the well-wishes.

Gentlemen,

I was checking the linings on my father's Camry and noticed that the front disc brakes exhibit the identical situation as our new Spridget DIY setup. That is, the studs do not fill the holes drilled into the rotor, and in the attached photo you can see that the PCD is not identical with the rotor drilling.

Instead, the centering appears to be accomplished the way I accomplished it in the above photos--by matching the center bore to fit snugly on the half-shaft.

So, we're in good shape. The DIY machining process really is simple, and the only trick is to go slowly, alternating test fits with chamfer and bore passes frequently.

Joel.

JM Young

In terms of the cost of conversion, here is a preliminary breakdown without adapter plates, and not including brake fluid and new gaskets and O-rings for hubs:

Used 1996 Nissan Sentra calipers with brackets, bolts, and banjo bolts: $65
Caliper rebuild kits: $6 to $14
New pads: $6 to $12
New hydraulic hoses: $12 to $25
New Spridget brake line fittings to fit Nissan brake hoses: $10
New 1996 Nissan Sentra rotors: $18 to $25
New yoke ends for shortened OEM brake rods: $18
Total: $169

I actually found semi-metallic pads for $3.64 (set) and Dorman hoses for $6.20 a piece on Rock Auto, so the above tally is conservative.

Rebuilt calipers with brackets and hardware are $146 for a pair on Parts Geek after core refund, so you're looking at $315 if you can't find used Sentra calipers (my situation).

Add $4 to $6 if you don't have a 1/4-28 die to rethread the brake rods. I figure most people who will attempt this own an electric drill or dremel and a little triangle or square file. A mini-tubing cutter, generic flare tool, and hub puller are the only other specialized tools involved, and are extremely cheap online.

There are YouTube videos online showing how to rebuild the Sentra calipers, but really all you need to do is replace the piston seal and boot, the parking brake cam seal, and retract the pistons, which requires a tool to rotate the pistons you can borrow from Autozone or if you live somewhere without stores like that, get for a few dollars online.

Can't wait to get the calipers in the mail and make the wood mock-up adapters. I already miss commuting in the Midget, and that disc rotor looks neat peeking out from behind the minilite!

Joel.
JM Young

Your father's Camry has the wheel centered on the hub, but spridget wheels cent on the stub.
Trevor Jessie

I meant spridget wheels are centered on the lugs. Or wheel studs for everyone else.
Trevor Jessie

Trevor,

Got it, thanks. Guess I was just relieved that the method wasn't something that isn't a standard automotive practice somewhere.
JM Young

This thread was discussed between 26/09/2014 and 13/10/2014

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