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MG Midget and Sprite Technical - Front brake upgrades

Hi all.

Basically long story short, looks like someone sheared the bleed nipple off a front calliper many years ago and it hasn't been touched since. I tried to get it out but it's well in there and incredibly hard!??

So il be needing a new calliper, makes sense to do both. So seeing as I am changing callipers anyway I was wondering if there are any bolt on upgrades that are cheap? Im not interested in spending Frontline or willwood money. Up to £200 maybe.

I have searched a fair bit and can't find anything really. It's already got ss braided hoses.

Cheers!
Karl Bielby

Karl, I have a pair of original calipers which might help you (1275-1972) but they will certainly need work.
I ditched them for Kent Auto Development 4 pots, which are beyond your budget.
How much are re furbed originals ?
P Bentley

A sensible upgrade to standard calipers without spending huge amounts is to use greenstuff or Mintex brake pads. New discs, pads, calipers and s/s brake hoses will set you back around £160 but give a noticeable improvement.
GuyW

Another vote for pad upgrade. It retains brake balance and is difficult to out run unless you want to end up walking.

Brake balance is important, if the fronts are uprated without doing anything to the back the result can be less maximum braking rather than more if front wheel traction limits are reached well before the back, as for max braking all wheels need to be at traction limit.

Though if the front pads on std discs are too hard then the rears will lock up too early.

Paul Walbran

Hmmm I thought so.. the pads fitted look pretty much brand new. Discs too.

I have never had rear brakes until recently because they were oil fed from the axle, which is now sorted hopefully withe seals and new shoes. So that will be nice!

I bet that calliper has been full of air since the hoses were fitted. Hopefully will feel an improvement over what I had before anyway!

I head bad things about having to warm the green stuffs up. How do the minutes compare? Are they the 1144's or something?

I think recon calipers are about 100 and there is no exchange which I find a bit odd..
Karl Bielby

Karl

If your pads and discs are virtually new, I would be tempted just to buy a second hand caliper from Fleabay or similar or persist with removing the nipple. If you cannot do it, any machine shop should be able. Recondition both calipers with a kit, clean everything up, and bleed them thoroughly. Clearly reinstating the rear brakes will further assist!

As for new pads, I would do the above first, test, and then see if you require them.
Oggers

I use greenstuff and its fine and no warm up needed,they are on a frogeye which is a bit lighter than a later Spridget anyway. Possibly one reason why there is no exchange is that the calipers are fairly common having also been fitted to 1100/1300 range as well as Spridgets. Big Red provide a repair service andyou can also specify the calipers in a range of cheery colours!
Bob Beaumont

The I looked in Bigg red earlier but they don't seem to list anything for the midget?

I was wondering wether to take it to a machine shop or garage that will be able to get some Oxy acetylene on it.

The caliper itself is spot on it seems. Both pistons fully retract nicely and there is no binding. Seals look good too so I wouldn't mind getting this nipple out if possible!
Karl Bielby

Also the quality of replacement callipers worries me... So if rather keep original!
Karl Bielby

Various suggestions to remove a sheared nipple as follows

Soak with penetrant overnight
Force a tight fitting drill bit or similar into what remains of the nipple
Mole grips on the bit - wind it out

Failing that as above - after blow torch application.

Failing that, if the nipple is proud, weld a nut onto it and remove with spanner

Failing that, carefully drill it out and re-tap, or drill larger hole, tap and fit larger nipple.

I would still recommend a thorough bleed regardless of whether you recondition or not.
Oggers

Once you have the calipers sorted - and new replacements are available at a reasonable price if needed. Then add stainless steel braided hoses. With well bled brakes the ss ones will give a firmer pedal feel than standard rubber hoses.

Correct REAR brake adjustment is vital in getting the fronts to work properly so don't neglect that.

If using Mintex or greenstuff pads then the point that Paul makes about front / rear balance is important. One easy solution is to fit mini rear shoes, - they are wider than Spridget ones but still fit the standard drums.
GuyW

Bolt on upgrades that are cheap? No, not in terms of changing calipers.

I had green stuff, wasn't impressed.

I have JLH's big brake fronts. They are great. But more than £200.

For a standard car, for road use, there's no need for anything other than a pad upgrade and SS hoses in my opinion.

I'd recommend fitting SS caliper pistons in the calipers. Fit and forget.
Rob Armstrong

Karl,
Guy and Paul in particular make very good points, I'd also add the obvious basics that can often be overlooked like a complete refill of the brake fluid (regularly) and to factor in good tyres that are not hard through age or lack of use, regardless of how much tread is on them.

Although greenstuff (EBC) are local to me I've never had their products but I've had a couple of sets of Mintex 1144 on my Midget and have been very happy with them.
Nigel Atkins

I see in post 1 that Karl already has s/s hoses so that just leaves calipers and pads. A pair of NEW standard calipers cost me £115 6 weeks ago. They seem fine, they've just done practice and 3 races at Angouleme with no problems.
https://www.youtube.com/watch?v=10jpO8LfAI0
David Smith

There are currently quite a few pairs of calipers on Ebay, ranging from second hand at £39.99 free postage and a couple of new pairs at £85 Inc postage.

As an aside, I have previously managed to bleed brakes with snapped off bleed nipples by doing it on the pipe.
Get an assistant to pump up the brakes and retain hard pressure on the pedal while you open the pipe union at the caliper and quickly close it at the bottom of the pedal stroke. Repeat as necessary. Watch out for fluid spray.
Bernie Higginson

I've done that too Bernie. The only trouble with that is you leave old fluid in the caliper which is the very place you dont want it if it is old and has picked up moisture.

Trev
T Mason

Karl
If you have some time to look around for a pair on Metro 4 pot NON Vented calipers this conversion can be done for under £200.

The calipers will bolt onto the uprights and give a value for money 4 pot conversion, . Another reason I like them because they have an almost "period" look as they are the same style of Lockheed caliper as the originals.

I also recommend Mintex 1144 pads as excellent for the road and having a bit of fun too.

Brake balance is v good with these, but your rears must be 100% good, I find that rear wheel cylinders seize up just when you arn't looking and need replacing at minimum every 3-4 years to keep them at their best performance but fortunately they are cheap.
Ian



Ian Webb 1973 GAN5

Those bleed nipples are most likely just pot metal or low carbon steel at best

id think you could hit it with some heat to release it ...probably a bad idea

but id think it would be easy enough to drill it and retap

of even drill it and take alot of the nipple out just leaving a thin ring next to the threads and use an easyout to removethe rest.

prop
Prop and the Blackhole Midget

As Prop says, carefully drill it out. The hole left by the snapped off nipple will give a good central location for the drill/drills. Start small and increase size until you get to just the thread of the nipple left.
Bernie Higginson

Another vote for Mintex. My 71 has original calipers, std discs and s/s hoses, gives a nice firm pedal.
It also has a servo but that opens up a big can of worms...
J Tickle

At just £40 each why would anyone even consider a recon or second hand pair - or even living (?) with dodgy ones

http://mgbhive.co.uk/product/20-new-midget-outright-caliper-17h94389-left-right-hand-side/
dominic clancy

For drilling out a left hand twist drill is preferred as it can grab and unscrew the offending part rather than trying to tighten it, especially when most has been removed. If I was drilling out I would remove the pistons so any swarf can be removed or mount the caliper so that swarf falls down out of the thread.
David Billington

David

Great point about removing the piston... do they make a left handed drill... thats a cool idea also

prop
Prop and the Blackhole Midget

Prop

Over here, as we drive on the correct side of the road, my motorcycle is right hand drive.....
Oggers

Yeh I think I just need to hit it with a left handed hammer!

Cheers for the suggestions all, as I said I have ss hoses fitted already, and the reason I found the sheared nipple was because I want to replace the brake fluid. So that's those 2 bits dealt with.

These mintex are sounding interesting, are they hard on discs?

Ian, this metro 4 pot idea sounds ace too, what discs do you use?

As I said earlier too, even a cobalt drill that was only slightly opening the hole down the centre, wouldn't touch it. It blunted 3 drills that I use to drill titanium!! Going to take into a garage today to see if they can get it out. If not, it be a new pair.
Karl Bielby

Dave just watched your video, goes well your midget! What engine/gearbox are you running?
Karl Bielby

Thanks!
It's a 1380 recently rebuilt by Peter May, 286 cam, Weber 45, BL SCCR box, and a 4.9 diff for that event.
David Smith

Karl

The NON vented Metro caliper fits straight onto the std disc setup. You say yours are almost new so should be fine.

Your s/s hoses should fit straight in also, 2 short loop hoses are needed to be purchased and also 4 banjo union, and some shim washers to centralize the calipers. Oh and some Metro pads

A small machining operation is needed to slot the holes in the caliper holes, its been done quite a lot and is perfectly safe on the cast iron caliper as there is plenty of material in the lugs . I have tried to attach a photo but the file appears to be too large, so I will take a new photo soon at a lower resolution.

The Mintex pads are not hard wearing on the discs.

It is possible to go the hole hog and fit the vented discs but that is much more work and anyway is exactly the same braking power but with the additional cooling of course, and a large unsprung additional weight penalty as the disc is fairly heavy, I have all the weights noted down if anybody wants to know. It would be possible to fit the non vented / std Midget disc and at a later date change to the vented disc setup using the same calipers with spacers fitted. I have fitted/used both setups.

One thing to note if you go searching for the Metro calipers a LH on a Metro is a RH for Spridget, and vice versa.

Ian
Ian Webb 1973 GAN5

Ian,

We have a Midget disc brake conversion on our Minor. It uses standard Midget steel wheel hubs and started off with standard Midget solid discs and Midget calipers. The calipers are mounted on a 'J' bracket that picks up on 3 of the 4 drum backplate holes.

Same as required to convert a drum-braked Sprite or Midget, without changing the uprights, but would you?

Drawing available for the 'J' bracket if required.

The first change was to Metro 4-pot non-vented calipers, as used on the early non-Turbo Metros, still using the standard Midget solid discs, and then finally to Metro 4-pot vented calipers and Metro vented discs.

The change to Metro calipers required a new 'J' bracket, as the Metro calipers have a different mounting hole spacing (3.25" for Midget and 3.50" for Metro), and also different mounting bolt sizes (7/16" UNF for Midget and M10 Coarse for Metro). Again drawing available if required.

The change to Midget discs, vented or non-vented, needs machining to both the Midget hubs and the Metro discs - I have drawings of what is required if anyone needs them.

We used some made up Goodridge s/s hoses with a loop between the 2 ports on the Metro caliper.

Initially used Mintex 1144 pads, but could get fade on track days, so now use Mintex 1155's, which seem to be bullet-proof! The Minor is heavier than a Midget, so 1144's may well give the same reassurance.

Both the 1144's and 1155's work straight from cold with good feel (we do have a servo to avoid the odd panic when jumping in from a 'modern'!).

Richard
Richard Wale

Richard/ Karl to fit the NON vented metro calipers to the std disc braked spridgets does not require any machining of the hubs or discs etc only slotting of the mounting holes in the calipers plus suitable high quality bolts (7/16 unf IIRC) This is in answer to Karl original request for a cheapish conversion.

In fact I have been running the vented Metro setup for many years until recently when I decided to try the non vented metro caliper plus the std spridget disc just out of interest to feel the difference.

Ian
Ian Webb 1973 GAN5

how about fade resistance though? I faded my standard brakes, and I wasn't sure that adding more pistons and pad area was going to help with that. I figured that vented was the way forwards, and that I wasn't comfortable with slotted holes on brake caliper mountings. Just don't buy any takeaways for 6 months and get the JLH kit...
Rob Armstrong

are these any good
http://www.ebay.co.uk/itm/Classic-Mini-Metro-4-pot-disc-brake-calipers-Pair-Four-Piston-Caliper-/262668325028?hash=item3d284090a4:g:ScQAAOSwLF1X~BNT
mark 1500 on the road Preston Lancs

Yep that's the right ones Mark. I was lucky I found some similar but completely refurbed them myself and also fitted ali pistons ( I needed some pistons anyway) so that the extra weight was reduced.

Rob the slotted holes are fine, many people have done it with no reported problems that I am aware of. I suggest it must be done by a competent machinist not with a hand drill !! I did contemplate slotting some aluminium MiniSpares calipers but they are much more accurately machined with very little spare material around the mounting lugs, so decided against and anyway there is always the KAD.....alternative at a price !

Ian
Ian Webb 1973 GAN5

Here is something I have been working on (that you already know about Karl).

DIY you could do it for £120 - £150.

Just finalising the CAD for the mounting brackets at the moment, and I found someone to do some laser cutting. Unfortunately after that I am not sure when I will find time for fitting and testing as I might take the car off the road for a few months.

Want to be a guinea pig?* :-D

Cheers,
Malcolm

*Any fiery vehicular death you may encounter from testing parts for me is purely coincidental!


Malcolm Le Chevalier

I thought long and hard, with all of the evidence of people who have done it and haven't crashed and burnt. I still decided against it :)

Malcolm that looks interesting. My advice would be to keep an eye on brake balance.
Rob Armstrong

I have looked into the metro option and it seems the mini boys have beaten us to it and hoovered up all the spares! Pretty hard to find any sent decent calipers! Looking at it I may struggle to do that on a budget after calipers, machining, rebuild kit, hose linky bits and pads..?


Took caliper to a garage today who had a go at it and just made a right mess of it.... So I definitely need new calipers now. Or drill it out and helicoil, but that will cost more than new calipers anyway!

And yes Malcolm I will more than happily be a guinea pig! Since I need new calipers anyway it makes little difference as to which I get (apart from slight cost)
Karl Bielby

£82 for new pair from moss and £55 for M1144's.. £137 for sorted standard brakes...
Karl Bielby

As promised here is a pic of the elongation required for the Metro calipers to fit Spridget mounting holes, They are necessary because as Richard says below, the Mini/Metro has 3.5" mounting holes but the Midget is 3.25"
This caliper was fitted for about 10 years of use and abuse with these slots.
Ian


Ian Webb 1973 GAN5

Second pic
Ian


Ian Webb 1973 GAN5

Ah so you have to drag each hole .125 closer.

I really like this metro set up. But it will exceed what I want to spend I think. Bearing in mind that it's only a fast road car (for now).

Although, did you notice much improvement over standard?
Karl Bielby

I'm not disagreeing that they work, but those pictures make me shudder.... Maybe that's just me.
Rob Armstrong

On Mini forums there is a lot of talk about fitting Ford Fiesta Mk1/Mk2 calipers to Mini's. Is it possible with Midgets as Mini's and Midget's share the same calipers?

Rob
Rob aka MG Moneypit

Rob has let the cat out of the bag! :-)

Well, the Ford bit is right.

Malc.
Malcolm Le Chevalier

Sorry, Malcolm. It was a quiet day at work and I had to look busy!!!

I suppose if you have to elongate holes to fit Metro 4 pots then there must be other manufacturers calipers that you can do that to.

How about the later Metro single piston calipers?

Also heard about Austin Princess calipers but apparently they are officially rarer than hens teeth.

Rob

Rob aka MG Moneypit

There was a two part article published in MASCOT about how to adapt and fit Metro 4 pot calipers. Written by Matt, AKA Tarquin who used to be a regular here on the BBS. Probably about 4 years ago now.
GuyW

It's OK Rob, it's not difficult to figure out if people really wanted to. The Fiesta mk1/2 calipers are a bit hard to get hold of, so I have gone for something a bit more up to date.

Malc.
Malcolm Le Chevalier

I never fitted the standard Midget calipers, as I went straight to the Midget solid disc and Metro 4-pot solid disc caliper combination.

The total piston area is virtually identical between Midget and Metro calipers, so no advantage from that.

On track days with the Minor I could occasionally fade the 1144's, but not the 1155's.

The change to the Metro vented discs was done as an interesting exercise to do, but I am not convinced that there is much obvious difference over the solid discs!

Richard
Richard Wale

We moved from solid discs to vented with our Minor kits as modified cars were able to produce brake fade , this being with Midget, Marina and Ford disc / caliper combinations.
Our 4 pot Ford based kit offers not only better braking but much improved feel, the std M/C can be kept and there is no requirement for a bias valve as the system is well balanced.
I share Robs concern over the method of modifying the Metro caliper
J L HEAP

That is this MASCOT thing. I see it all the time and it apparently has loads of good info on it.

The metro idea sounds good, but I don't like those ovalised holes either really.. plus they are fairly rare.

Dad wants it out of the way to do some stuff in the garage so I might have to go down the stock route for now... :-s
Karl Bielby

Karl, do you mean what, rather than that ?

MASCOT is the monthly magazine of the Midget and Sprite Owners' Club.
Web site here: http://midgetandspriteclub.com
GuyW

Yeh sorry, bloody auto correct..!

Cool il check it out!
Karl Bielby

Malcolm, the disc looks to be 300mm but the PCD looks quite rare. Did you not have other choices?

Rob
Rob aka MG Moneypit

Giving the car a once over this weekend and the rubber brake lines that are only 5 years old are starting to show signs of age .Is it a worth while upgrade to fit s/s ones and upgrade the pads either mintex/greenstuff .
mark heyworth

Yes. Ss lines are particularly good. The only disadvantage is that you can't clamp them to stop fluid coming out.
Rob Armstrong

sorry Rob, you have lost me...
Malcolm Le Chevalier

I looked at the pic you posted and worked out the disc dimensions. 300 mm diameter and 4 x 130 mm PCD but they only fit VW Beetles (Old ones). Or have I worked out the wrong dimensions?

Rob
Rob aka MG Moneypit

300mm sounds a bit big for a 13" wheel.
Dave O'Neill 2

yes, it is a bit big. Rob it's bolted on with the disc bolts, not the stud pcd, which I think is where you're off on the wrong foot a bit.

My 260mm front brakes won't fit under 13 inch wheels...
Rob Armstrong

Oh yes, didn't think of that. I'll revisit it tonight.

Rob
Rob aka MG Moneypit

they are 240 mm. the normal mounting holes on the disc aren't used and new holes are drilled to the usual spridget pattern.

Malcolm
Malcolm Le Chevalier

some here if yu still need them

http://www.ebay.co.uk/itm/MG-Midget-Brake-Calipers-1275-/291914198829?hash=item43f7712f2d:g:jpUAAOSwpLNYBSEg
mark heyworth

Cool, how much do you want for them?

I think I'm going to have to go for stock calipers and decent pads due time constraints...
Karl Bielby

they are not mine just saw them on ebay
mark heyworth

Ah OK cool. I'm going to need them before Friday! Moss it is.
Karl Bielby

New calipers and pads fitted. The passenger side caliper seems to be binding slightly, going to give it chance to settle down before I do anything.

Bled a load of vile old fluid out and flushed with new fluid. Went for a spin and it seems to have moved some air around somewhere as the pedal really pumps up now. First application and it's almost to the floor, 2nd and it's nice and firm where it should be.


But, my god what a difference those M1144's make! Takes less than half of the pedal pressure to lock up, no longer need a man foot to bring it to a stop!


So hopefully one more quick bleed and it should be all good!
Karl Bielby

Just looked on Peter May website for the type 900 big brake kit. It is now for wire wheels ONLY.

http://www.petermayengineering.co.uk/specialistProducts.htm

Not sure why?

Rob
Rob aka MG Moneypit

I *think* he was going to drop it altogether as there are 2 better options, but then realised that would leave nothing for w/wheel cars so retained it for w/w only. Maybe.
David Smith

We are developing a wire wheel version of our kits ready for the New Year.
J L HEAP

Well the price of the Type 900, if it did solid wheels, would have been OK for me. The other two options are however out of my price range so I won't be bothering.

Rob
Rob aka MG Moneypit

Through out this tread no one has mentioned MGB calipers with Spit rotors. Where would this combo fit as an upgrade? We don't have easy access to Marina and Metro parts over here.
J Bubela

I picked up the MGB and spitfire disc upgrade, i'm interested in J Bubela's question, I wondered if it was possible to swap out the mob calliper for a lighter alloy wildwood calliper for example, if the mounting lugs are the same etc? That would be a much better upgrade.
Jon White

"Throughout this thread no one has mentioned MGB calipers with Spit rotors"
I thought (perhaps mistakenly?) that was the basis of the PMay 900 kit?
David Smith

yes, it is David. MGB calipers and modified spitfire discs, plus a bevvy of spacers etc.
Rob Armstrong

Yes the PMay 900 are MGB/Spitfire. I've done a bit of research and the Spit disc needs turning down to 9 inch diameter. It also needs a little machining in the centre to clear the MGB caliper. Also, you need a spacer behind the disc to get the disc in the centre of the caliper, and also the steering arms may need to be spaced to stop the disc from touching the TRE and lastly, the trunion needs raising a tad for the same reason.

MGB V8 calipers can be used but may not fit all wheels due to a bulge in the casting.

Rob
Rob aka MG Moneypit

Other calipers that fit without machining.

Austin Ambassador/Princess 4 pots. Very heavy and getting rare as they are liked by Ford enthusiasts. Also they are dual feed but it's easily solved.

Rover SD1. Very similar to above and I think some made it to USA. SD1 Vitesse are better due to larger brake pads but give a lot of pedal travel due to bigger diameter pistons.

As Ford enthusiasts fit Princess 4 pots (with bigger discs than you can put on a Midget) it seems that Ford calipers must fit Midgets. Hence Malcolm Le Chevalier's approach seems promising.

Rob
Rob aka MG Moneypit

I have to say, for a fast road car, I cannot see a reason for needing more power than good stock with those pads. I definitely see that on track its a different matter as you are dealing with much more heat more often.

I can easily break traction now and will be upgrading tyres next time! (God knows what to though!)

Thanks for everyone's input in this thread! It's been pretty interesting!
Karl Bielby

Karl,
don't forget the point made by others about balancing the front pad upgrade with an upgrade of rear shoes, not urgent but a very good idea when possible. However four good tyres could possibly help more with braking and help with steering, suspension, road holding, handling ride quality and noise.
Nigel Atkins

Can you get upgraded rear shoes? I did search when replacing but found nothing!
Karl Bielby

See Guy's second post near the start of the thread.

There are also quite a few 'what tyres' threads some of the tyres mentioned in the threads going back even a few years are sill available, don't get too hung up with the new tyre labeling scores as some good tyres didn't get the best scores, whereas now, talking as a cynic, manufacturers know how to get the best scores for their tyres on the tests.
Nigel Atkins

Most tests are self certification too, so really only a rough guide!
Rob Armstrong

Cool il have a search for tyres threads!

Ahh yes I knew I read that somewhere, if read through the whole thread several times looking for it. Don!

Is there any particular year/model of mini or are they all the same?

Ta!
Karl Bielby

Found these on fleabay.

http://www.ebay.co.uk/itm/CLASSIC-MINI-4-POT-ALLOY-BRAKE-CALIPERS-8-4-C-AJJ4022-O-S-N-S-1984-00-PAIR-2F5-/381698609002?hash=item58df028f6a:g:MdsAAOSwAPlXg2PV

£250 a pair!!!

Any use?

Rob
Rob aka MG Moneypit

Same as metro, need holes enlarging
Rob Armstrong

Or how about these?

http://www.hispeccalipers.co.uk/ul4pri.html

£267 a pair inc postage.

Rob
Rob aka MG Moneypit

Anyone know anything about Landrover Defender 4 pots? Dimensions? Are they a development of Rover SD1 4 pots and are they likely to fit Midgets?

The reason I ask is that currently you can buy a new pair of 4 pots for vented or solid discs for about £90.

Rob
Rob aka MG Moneypit

Hi Rob, a very quick google suggests Defender discs are 298mm diameter. So the calipers will be designed to work on such a disc size, therefore would probably be too big to work on a disc that would actually fit within a Midget wheel.

I might have a further look into this though.

Cheers,
Malcolm
Malcolm Le Chevalier

I suspect that they will also be devastatingly heavy.
Rob Armstrong

I was recently looking into alternatives to the Princess 4-pots and came across Land Rover and Sherpa van calipers. I hadn't got as far as checking dimensions, but noticed that Brown & Gammons were selling Land Rover calipers on eBay.
Dave O'Neill 2

I did a bit of googleing but the only thing I can determine is that Defender 90 uses 41mm pistons and 110 and above use 46mm pistons. Still not determined lug spacing but it seems that it is common to most land rovers and range rovers so no-one says "you need to re-space x to y",

The Hi-Spec UL4 is a little marginal for the weight of our cars (770 Kgm) but http://www.hispeccalipers.co.uk/b4pri260.html are ok (1250 Kgm) but are consequently dearer at £336.36 a pair.

Going back to disc size I suppose it depends on how far away from the centre of the hub the caliper mounts but for calipers designed for big discs used on small discs there is a risc that some of the pad material will overhand the disc due to the curvature designed into the caliper.

The Midget has a particular problem with big discs in that they fly close to the trunnion and steering arm. This could be solved by spacing the disc away but that introduces other problems and consequently increases the cost.

A bit of a rock and hard place situation.

Rob
Rob aka MG Moneypit

The Hi Spec Billet 4 Princess caliper is used by Frontline with their 9" disc set up. You will require 3mm spacers to obtain the correct location for the disc. Apparently Frontline are not bothered about the pad over hang as the 'rough casting on the disc removes the excess pad material'. There was a Frogeye parked in the MASC area at the Silverstone Classic this year with this set up fitted.
Motley 5

Rover SD1 calipers have 41mm pistons. Princess have 38mm pistons.

Rob
Rob aka MG Moneypit

For information http://www.jlhmorrisminors.co.uk/mg-midget-parts.html
Our kits are simple to fit, and include new alloy hubs with taper roller bearings, for less than the FL kits. All high quality materials and parts, proven on road and track.
J L HEAP

If jlh hadn't posted that, Then I would have. There are enough different (safety critical) variables to make the "I wonder if this works" approach questionable, even for me. If you have the cash, buy the brake kit. If you don't, drive slower till you do ;)
Rob Armstrong

Well, after doing a bit of reading and web research the only real solutions to improved braking are better pads, bigger discs or thicker discs or any combination of all 3.

Bigger pads do nothing to improve braking save a slightly better distribution of heat into the disc.

4 pots give a slight improvement because having smaller pistons the centre of pressure on the disc moves closer to the edge hence a slight increase in leverage.

Better pad material delays the onset of fade as do thicker discs and vented discs, but you can't go too far with a road going car because they work best at a range of temperatures that may not be reacheable on the road.

Bigger (diameter) discs make the biggest improvement as long as the centre of pressure of the pads moves out towards the edge of the disc to take advantage of the extra leverage.

But ultimately, it's the grip the tyre has on the road that is the limiting factor.

Rob
Rob aka MG Moneypit

You could look at boundary layer breakers. An old racer I used to know told me they used them on a race car and they worked well and gave near vented disc benefits for little cost, they were on a budget at the time. IIRC they were a thin wire or strip that ran close to the disc maybe 1/3 the way around the disc from the caliper and peeled the hot boundary layer away from the disc surface to allow cooling air to get at it. I don't know how practical they would be for a road car though but maybe not much harm in trying.
David Billington

That sounds interesting, any pics of such devices? I'm thinking about making some kind of cooling system for them anyway.
Karl Bielby

This thread was discussed between 10/10/2016 and 16/11/2016

MG Midget and Sprite Technical index

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