Welcome to our resource for MG Car Information.
MG MGA - AP Caparo master cylinder
|Awhile back, I posted comments about a Moss acquired master cylinder in which the brake piston, while bench bleeding, took 20 seconds to return after pushing it in fully and releasing. I returned it to Moss for credit and then purchased an AP Caparo cylinder elsewhere. |
Yesterday I bench bled the Caparo cylinder and it took 7-8 seconds for the brake piston to return after pushing it in fully and releasing (silicon fluid used with both cylinders).
Is the time duration on the Caparo unit acceptable?
I don't understand what you mean by 'bench bleeding'. Do you mean just filling the reservoir? If so, what did you then do? Were the blanking plugs still in place or did you end up with fluid all over the place? If the plugs were still in place I would expect the pistons to move very slowly.
|I put in a new cylinder a few weeks ago (not the AP CAPARO one) and the pistons return immediately. Anything else and your brakes / clutch are going to drag. That's obviously not going to be satisfactory. The new AP Caparo is obviously still no good and should be returned.|
Exactly my experience with my AP Caparo 3 years ago. Straight out the packaging and worked as you describe (without any fluid). Then the same after installation and system bleed in the car. That's why I am questioning what Rick's 'bench bleeding' involves.
|Thank you (!) for the input.|
Steve; "bench bleeding" (a different term may be used in the UK?) a master cylinder is an effective way to remove any air from the unit while it's in an accessible (on the "bench") position before installing it onto the car. It also provides an opportunity to check that the cylinder's operating properly before going through the trouble of installing it. It's usually done by placing the cylinder in a vise, and replacing each of the two blanking plugs with a fitting, provided with a bench bleeding kit, that has the proper threads on one end to screw into where the blanking plugs were, while the fitting's other end has a male extension onto which one end of a flexible tube fits over. The cylinder top is removed and the other end of the flexible tubing goes into the cylinder resevoir; the one tube from the fitting screwed into the clutch outlet, and the one tube from the fitting screwed into the brake outlet. You then put fluid into the resevoir and push the clutch and brake pistons in and releasing (simulating pushing in and releasing the clutch and brake pedals) I use a phillips screwdriver for this, pushing in where the push-rods that connect to the pedals would push in. When you do this, the fluid exits through the special bench bleeding fitting, through the tubing, and back into the resevoir where the tubing is submerged. As you push in, air bubbles are immediately evident, becoming less and less as you push and release until finally there is no evidence of air bubbles. The cylinder is now "bench bled" and ready to install, making bleeding the whole system a lot less troublesome.
In my case, when I first placed the Caparo cylinder in the vise, I pushed in and released both the clutch and brake piston before adding any fluid and both pistons returned immediately.
After adding fluid, the clutch piston returned very quickly also; no reason to suspect anything amiss there.
However, after adding fluid, the brake piston takes an extraordinary amount of time to return after pushing in and releasing; 7 to 8 seconds yesterday and, after leaving it overnight, it took upwards of 20 seconds to return today.
Another thing I noticed was that residual fluid is leaking past the gasket under the front plate where the pushrods enter the cylinder, even though both of the securing screws have adequate torque, and, come to think of it, is it even normal for fluid to BE there to leak out in the first place...
I don't know.. Starting to feel a bit deflated and discouraged, but it comes with the territory, working on these cars. Ignorance doesn't help. The Moss cylinder had the same problem with the brake piston and now it looks like I've procured the only faulty Caparo unit out there. Could it be the silicon fluid? Has anyone had problems with a new cylinder using the silicon fluid? I'm grabbing at straws.
Would it cause irreparable damage if I used regular non-silicon fluid on this unit for bench testing just to see if the brake piston returned normally?
Anyway, any thoughts, insights, or suggestions welcomed.
I emailed Bob West (got it from him) about the problem and am awaiting a reply.
I know this's been long-winded; thanks for hanging in there.
Not normal for fluid to be behind the piston, The rear cover plate does nothing to seal the cylinder, it just keeps the pistons from popping out, and provides an anchor point for the dust excluder boots. I never understood why they use a gasket there, except maybe to stop a "click" as the pistons return smartly and hit the end plate, or to prevent corrosion where pot metal contacts iron.
"Return smartly" being the Operative Term here.
And, the clutch and brake cylinders are entirely distinct from each other, save being in the same lump of metal. No reason to push them down in unison.
|Rick, I also bought a Caparo m/c from Bob West. Not tested it or installed it yet, but I might try it as described.|
|I keep learning something new; thanks, FRM,, you've confirmed my suspicion that fluid shouldn't be leaking past the piston and seeping through where the front plate mates with the cylinder.|
Art; you may already know this, but if you bench bleed your cylinder, you can pick up an inexpensive bench bleeding kit at your local parts store. It'll come with a number of those "fittings" I referred to, coming in a variety of sizes. They'll usually have a listing of the different sized fittings somewhere on the packaging. You'll need at least one, preferably two, (1 for the clutch outlet & 1 for the brake outlet) of the 3/8x24 sized fittings. If you decide to give it a shot, let me know how long it takes for the brake piston to return after pushing it all the way in and releasing, with brake fluid in the reservoir, and what type fluid you use. :)
|You do not need to buy fittings, use cut off bits of line with old fittings. |
No need to bench bleed these cylinders either. I was about thirty years in before I ever heard the term.
As I said, no connection between brake and clutch, so you only need one if you do bench bleed.
"Return smartly" being the Operative Term here.
Right now, fast, without delay.
I think you have a secondary seal turned inside out on your brake side.
Thanks for the description. Like FRM, not something I had heard of nor had any reason to do on the bench. I just installed my unit dry in the car, filled with fluid, allowed to settle, then bled.
I feel bad about this as I have always pushed the AP Caparo unit as being top class. Indeed, until this issue with you, I have heard only praise about it.
That said, something inside me niggles and asks the question why? It appeared to work upon receipt in exactly the same way as my unit. From then on, yours went down hill. You also had a similar issue with the Moss unit. Is there a common factor?
In WW2 RAF Tempest fighters started crashing for no apparent reason. They thought it was a design fault until one sharp eyed investigator spotted a worker on the production line levering the elevator control wire onto a pulley, damaging some wire strands in the process. After about 10 hours use, the control wires were snapping!
In your bench bleeding process did you take the units apart for inspection before carrying out the bleeding? Could there be fluid contamination? Has your bench kit been used previously with mineral oils? If so, has it all been cleaned out with acetone or a similar cleansing agent? Has your silicon fluid ever been in contact with other fluids? etc.
|I would take the unit apart (pull the pistons out) and check that all the rubber is intact. I had a rubber skirt on a brand rebuild kit tear off.|
All of the previous reports of the APC M/C units that I have heard say that they are excellent units.
JIM in NH
|Again, thanks for all your feedback...|
Where can I source/buy AP Caparo master cylinder rebuild kits? I'm looking for a source that sells kits whose contents are identical to the innards of the Caparo unit. Thanks.
|That's ok, disregard my last post; I located a source.|
As I got worried after reading the thread concerning the information of problems with the TRW MC I contacted Moss in England asking what to do.
I must say that I am very impressed over the help I got. I was able to send my old TRW, still in it's unopened plastic bag, six years after I bought it in Bristol, back to Moss and got myself a new one from AP Caparo!
Now lets hope that this is OK because I don't think that Moss are willingly to do this a second time!
|Anders, you were lucky. Moss wouldn't refund my brake line which was wrong due to a catalogue error, b/c it was > 12 months ago.|
|Moss USA has a 24 month return policy on everything. Call them again. Moss UK may be different.|
|Rick, Did you ever sort out your problem? Three weeks ago it seemed that you were about to get a new set of seals. If so did this cure the slow piston return on the brake line?|
I'm asking because I think I may be having a similar problem. I haven't replaced my master cylinder but have new seals and have changed to silicone fluid...........................Mike
|Sorry Rick I was half asleep and didn't read your recent thread from which I assume you have no results yet!.................Mike|
In the beginning my intent was to replace the entire hydraulic system and switch to silicon fluid. Included with all the necessary parts was a new master from Moss and, when bench bleeding with silicon fluid, the brake side took upwards of 20 seconds to return on the new m/c. I posted here and got a lot of feedback and, in the end, returned the Moss m/c and ordered a new Caparo m/c from Bob West.
When I bench bled the Caparo unit with silicon fluid, the same problem came up, ie: return of the brake side piston took WAY too long, again upwards of 20 seconds to return. Changing to a different brand of silicon fluid made no difference.
I wondered if the same problem would occur with non-silicon fluid, and, since the Caparo seals had been soaking in silicon fluid for days, I ordered a couple rebuild kits for the Caparo unit and some Castrol LMA fluid.
The rebuild kits have arrived, but am still waiting for the Castrol LMA fluid to arrive and will test the Caparo unit with the Castrol fluid when they do.
I really wanted to go the silicon route to avoid paint issues, but I've become weary of dealing with the problem, so if the slow return brake piston problem does not occur with non-silicon fluid then I'll proceed with the project using Castrol LMA.
I'll post the results here. Weeks can, and do, go by just waiting for parts so, if you like, you can send me your email and I'll let you know the results to avoid checking this site repeatedly for them.
|Just post them here...we're all interested!|
IMHO, should the Caparo master cylinder work correctly with new seals kit and conventional mineral fluid, I would caution against directing the blame towards the previously used silicone fluid. Seems to me most unlikely that any type of fluid would be the culprit, much more likely the seals or some other mechanical gremlin. Many of us have used silicone fluid very happily for years. Pity you are changing two variables at the same time and then having to decide which is having the effect. Of course, neither variable might be the solution! I hope not - good luck with your investigation.
|I used Silicon with my Caparo from day 1 and never had any issues. No bench test. Just installed it and it worked a dream. 3 years on no issues. Been a silicon user for 16 years. Never had a problem due to silicon.|
|Like Steve I used silicon fluid in my Caparo six years ago and no issues since. I fitted another one last summer and it was the same. Like most I have never had any issues with silicon fluid. I have seen plenty of old leaking and sticking cylinders with DOT4 though.|
|I'm forced to agree with you; why am I having these difficulties with the dot 5 while there are all of you out there who have been, and are, using it with no problems?|
While doing more research, I ran across this excerpt from one of a long string of info out there:
".....All brake fluid, glycol or silicone based, must swell brake system seals to form tight seals and help prevent leaks. The maximum amount of swelling is also specified in the FMVS 116 testing. This defines a range of seal expansion that is “within tolerance.” This also means that different fluids can react with a given type of seal differently and still be within the specifications. Just because the fluid you are using is working fine does not mean another brand of brake fluid, even one that meets the same specification, will work just as well because it may not affect the seals in exactly the same way...."
Apparently, not all DOT 3, 4, or 5 fluids are EXACTLY the same, respectively, across all brands.
So, could I ask you (all) a favor and let me know what brand name silicone based fluid you are using that is working for you?
(What I've used so far is Carquest DOT 5 and Blue Magic DOT 5)
I have used Automec Dot 5, reference ABF004, for many years now. From memory, I think Bob West put me on to it. Made in USA and states compliance with FMVSS 116, ISO 4925 and latest DOT 5 specifications. The only caution evident on the bottle label is -"compatible with the seals and hoses used by all vehicle manufacturers except those few who specify mineral base fluids for some of their Citroen and Rolls Royce vehicles".
Hope this helps.
|It should be an easy test to measure the swelling by immersing a seal in the fluid for a few days, and end this discussion profitably!|
|I too have used Automec fluid since the car was restored in 1989. I suspect my black gunge issues were down to old age in the seals, which is why I replaced the whole cylinder with the Caparo one - I must get it bled in the next few days, it's been in the car for about three months, but bitterly cold and too much salt around to drive.|
The Lockheed cylinder I bought in 1988 is now on Malta, and I hope Frank has found seals to do a recon because the bores were fine.
|Automec for approx. 35k km with many Alpine passes o).|
Thanks for your responses.
I did a web search and came to realize that apparently all the distributors of Automec are in the U.K. Odd, given that it's made over here. More searching makes a case for it being the primo silicone fluid out there.
I left an inquiry with the entity that produces the stuff to see if it's available over here in the U.S. They may or may not respond.
Any satisfied silicone users over here that can relay the brand they've been using?
|I've used several brands of DOT-5 over the past 25 years. Bought them from various auto parts stores. They all seem to be equally good. The standards for production of all types of brake fluid are very strict. I doubt you would ever find bad brake fluid anywhere. Just keep it sealed up tight if it won't be used for a while.|
|" I doubt you would ever find bad brake fluid anywhere."|
Sorry Barney, wrong.
|Oh boy. So now we have to start listing sources for bad brake fluid? Where did you find bad brake fluid? Is this something predictable, or do you have to laboratory test even container purchased>|
|I've also used Automec on mine; it's the one that Moss supplies over here. I've no driving experience with it yet but when bleeding the brake line a couple of weeks ago I noticed, like Rick, that the piston return was slow. It wasn't anywhere near 20 seconds, I didn't time it but it was around a few seconds, enough to make me think it wasn't right.|
The new seals I bought from Moss some years ago but the m/c came with the car and was good when I first drove it. So I've got new Moss seals with Automec silicone. I've convinced myself that the piston delay won't be a serious problem. For one thing the piston travel will be much less after the bleed nipple is tightened and any brake drag will only be on the front because of the strong return springs on the rear shoes. Maybe I will have to renew the disc pads a bit sooner but that's not a difficult job.
Going back to the 'bench bleeding' technique this may not be too similar to 'in situ' bleeding because the piston travel will be greater if it is pushed right to the end of the cylinder with a hand operated rod compared to the movement with the brake pedal Perhaps also the cylinder bore is a bit tighter at the end if the honing doesn't reach that far. I would be inclined to put the m/c back in the car and see if the piston delay is the same..................................Mike
When I rebuilt my original master cylinder a couple of months ago I used what appeared to be a generic silicone fluid I found at Autozone: http://www.autozone.com/autozone/accessories/AGS-11-oz-DOT-5-brake-fluid/_/N-25ah?itemIdentifier=540132_0_0_
I've had no problems with seals swelling since using it (all new seals throughout the system.
|Again, thanks for all your comments and ideas.|
That's a really good point, Mike; ie: pushing the piston in all the way by hand vs the amount of travel the piston would go when pushed in via the brake pedal movement.
However, several times, regarding the push in - release - wait cycles that I went through during the bench bleeding thing, I held the tool (that I used to push in the piston) in my hand lightly, and just barely in contact with the piston as it was returning, in order to feel the rate of return, and the rate of return felt the same throughout the return travel, except for about the last centimeter or 2 when the piston would hesitate for a second and then snap home through that final centimeter(s) with a barely discernible clunk/pop. I also pushed it in about the same distance it would travel by brake pedal and the return rate was also the same. So, it looks as though the rate of return would be the same for the return distance resulting from the brake pedal push as it would for the same distance by my pushing it in by hand on the bench.
At any rate, what with waiting for parts, attacking all the variables, and the usual stuff that life dishes out, it'll probably be awhile before I can come up with any "Aha!.." moments regarding the problem's solution and it's a sure bet that it'll be posted here whenever that blessed event occurs.
Again, thank you for all your suggestions, comments and help!
|One last comment.|
I received a response to my inquiry regarding availability of the Automec fluid in the U.S. It follows:
Me: Where in the U.S., or, preferably, where in the San Francisco bay area, can I purchase your Automec dot 5 silicone brake fluid? A web search gave the impression that all the distributors are in the U.K.
Them: Thank you for your inquiry.
We do not supply any distributors in the US as the fluid is manufactured in the States so it will be probably be available under another brand name. We market it in the UK and across the world but our trade customers in the US do not buy it from us. We can supply you by mail order from here and the price will be £38.75 plus postage of £14 by Airmail.
Otherwise it may be worth contacting Moss Motors in California as they may supply another brand but make sure it has a DOT5 rating which is specific to silicone brake fluid. Any 5.1 rated fluids are a higher specification polyglycol fluid.
Customer Services Manager
T: +44 (0) 1280 822818
F: +44 (0) 1280 823140
Automec Equipment & Parts Ltd - Worldwide suppliers of Automotive Equipment
36 Ballmoor, Buckingham Industrial Park, Buckingham, Buckinghamshire, MK18 1RQ, United Kingdom
Incorporated 1975 VAT No. 301 8349 82
Sounds like there's some internal memo preventing them from spilling the beans regarding who sells the fluid that Automec puts their brand name on but has a different brand name in the U.S.
You'll notice I made no reference to British sports cars, yet she suggested I contact Moss in California.
The silicone fluid sold by Moss over here is labeled Cartel.
Although it can't be proved at this point, her response to my query would seem to indicate that Cartel silicone fluid is the same as the fluid labeled Automec in the U.K. Cartel is available from several sources besides Moss. I don't pretend to make any claims regarding the accuracy of my deductions; I only put this out there for what it's worth.
|In the 70s Dow-Corning and General Electric used to be the only manufacturers of the fluid. May be there are others now, or maybe just Dow?|
Don't know... Dow-Corning doesn't appear to sell brake fluid (anymore?), and Dow Chemical (a separate entity?) provides DOT 3, 4, and 5.1, but no DOT 5 (silicone over here) fluids.
There is, however, a company, corporation, whatever, that's called Cartel that, from all outward appearances, may actually make the stuff, and could be where Moss gets it's silicone fluid. Their website follows:
Don't know if this is helpful or not but, given this curious situation of a well-regarded (Automec) silicon brake fluid here in UK which comes from the USA but is not available in the USA, I could not resist the curiosity of having a quick chat on the phone with Automec. Given that I live in the UK! The guy who answered was aware of the issue, and clearly knowledgable, but was not prepared to divulge who supplies them from USA but strongly felt that Dot5 silicon fluid is readily available over there from many reputable big name suppliers and is to a strict formula and technical characteristics so should be no problem. So much so, that Automec have never conceived of the need to supply it back to the USA from where it came. I know this leaves bit of a difference of opinion between Barney and FRM but I also know what I would do in your position - just go out and buy Dot5 from a decent name and put it to work. Otherwise you would need to get some Automec shipped over.
|Well, FRM, -- Are you going to tell us where you got the bad brake fluid, or do we just consider it to be an anomaly and forget it?|
|I thought the following made an interesting read: http://www.type34.com/library/26-technical-mechanical/584|
I will, but it is not simple, and is both anomalous and systemic. Steve's linked article is fair, but has errors and missteps, so I will address that as well.
I am right now in what I hope is the final stage of an ordeal of 9 months, involving extortion and highway robbery by the City of New York, beginning with them towing my daughter's car = MY car and license plate, and everything I own is involved. Not fun, not happy, more poor, pissed! But I think it is nearly over.
Day or two, promise!
|Good luck Fletcher. Non illegitime carborundum.|
Thanks for the input. :)
Makes sense and sounds right, but the problem that started this thread occurred while I was using first one brand, then another of silicone fluid. The fluid that's labeled Automec appears, from searching around, to be the most well regarded of the silicone fluids out there. (Don;'t ask me what that means or how or why it may or may not apply to my problem; I'll admit at this point I'm grasping at straws.)
Given that most of my findings on the web point to Cartel being the people that ship the fluid over there where it morphs into Automec, I ordered a quart of Cartel & will give it a try with new seals.
One last chance for silicone fluid.
If that doesn't work, I'll try DOT 4 with new seals.
If that doesn't work, I'll know the problem isn't associated with brake fluid, and, at this point, I don't even want to think about the road beyond that...
Regarding the slow returning brake piston above; there's another observation I didn't mention that may trigger an insight into the problem. (Clutch side's ok)
With no fluid in the brake side reservoir and the holes at the bottom of the reservoir exposed to air, and nothing other than a splash of fluid in the piston bore to facilitate lubrication, the piston moves freely in and out.
But when I place a small (a couple tablespoons) of fluid in the brake side reservoir, covering the holes, and push the piston in, it either sticks where I stopped pushing on the first try (a little jiggling and jabbing on the piston will get it to return in spurts) or as in earlier posts, returns very slowly. It will remain like this until I remove the fluid from the reservoir. Once the holes at the bottom of the reservoir are once again exposed to air, the piston starts to move in and out freely again.
Does the above trigger any insights into why the piston gets stuck?
|Rick, Have you considered that maybe your piston return spring is a bit on the weak side? It sounds as if you may have a borderline situation during return and any air is just that much easier to move through restrictions than is brake fluid. I suppose if you've tried more than one m/c (and spring) this may be unlikely.|
But you could try measuring the spring force by compressing it on a pair of kitchen scales. If you don't have a second spring to compare perhaps someone on this site has a spare and could do the same measurement on one. I would do it myself but the thought of stripping down my master cylinder again after just bleeding the system doesn't thrill me.
If you are hesitant about replacing the silicone fluid and returning to glycol I can tell you that I've now had two accidental spills of fluid on my freshly painted heater shelf and if I had not used silicone I would be tearing my hair out..............Mike
|Surely this is what you would expect when doing a bench test. For a start you have the valve cap in the braking side of the MC moderating return fluid flow. Also you have no return pressure being applied that you would normally get from the rear drum brake springs forcing the pistons back in the wheel cylinders etc.|
|Mike: No, I doubt if it has to do with the spring strength, but thanks for the input, and, like you, I favor silicone & will keep at it. |
Steve: When pushed in and released, the piston currently stops 5/16 inch short of full return before contact with the end plate. If the unit's in the car as is and I went to bleed the system, it could still be done, but when applying the brakes, it's starting point would still be shy of that 5/16 inch as it started to push the fluid and expand the shoe springs, so, when the brake springs return and push the fluid back, the pressure build-up pushing back would return the piston back to the same position as at the start of the cycle, ie: the brake springs will return only as far as they were pushed out. FWIW, the (secondary?) seal just forward of the m/c return spring covers the smaller of the 2 orifices at the point where the piston's stuck. If I can just get it to return fully...
I don't know: you people have got to be tired of hearing about me and my godamn master cylinder. It's getting embarrassing.
I'll keep at it until I solve it or send it out to a specialist and it can be his problem.
I had/have a similar problem with my Magnette MC which I had re-sleeved in SS. I believe it is due to the quality of the honed finish in the bore not being fine enough.
To begin with, the pistons would stick at various positions in the bores until I had worked them back and forwards multiple times. Fortunately after I fitted the MC on the car the pistons would return fully but with a slight delay.
I have been advised to polish the bores to eliminate this problem but removing the MC on a Magnette is even more of a PITA than on the MGA. I will wait a while to see if it improves with continued use.
Fortunately it does not cause my brakes to drag, but the clutch is sometimes slow to engage.
(I am using silicone fluid)
I still think you are testing in a non realistic scenario. It's one thing to bleed the system, but to expect the piston to work to correct timings etc is another. In my opinion the lack of residual returning line pressure is stopping the piston short of its end stop. The internal MC spring has done most of its work but as its force decreases nearer to its uncompressed length it needs the returning line pressure to help it go that extra 'inch'. Currently the piston and spring are trying to draw ambient pressure fluid through a flow restrictor (valve cap). It's a bit like a conventional engine sucking the fuel mix through the carbs compared to a supercharger ramming it in.
Either that or you have something like the secondary seal on the wrong way round.
|Another way of putting it: the force exerted by the piston return spring on the valve body and valve cup is holding that assembly firmly against the valve washer, preventing or restricting fluid flow back into the MC. In normal operating conditions there will be strong fluid pressure from the return line to open the valve body sufficiently to allow the fluid back in much faster.|
You could test this theory of mine by removing the valve cup, then repeating your tests.
|To test Steve's theory, arrange the MC discharge pipe to connect to a vertical pipe which would supply back pressure, about 0.4-0.5 psi/ft.If you don't have enough room, pipe it into a vessel you can back pressure with air.|
|You all are narking up the wrong tree here.|
FR Millmore wrote:
"No need to bench bleed these cylinders either. I was about thirty years in before I ever heard the term".
I'm with FRM here (sort of). I had never bench blead a master cylinder for decades, until about 10 years ago when things went awry with some repacking kits making the piston stick in the bore. There have been some other issues with new master cylinders in recent years, but this is the first time I've heard of a new one with sticky pistons. Until now I though this problem was limited to repacking kits.
The "non return valve" is improperly named. It should be called "slow return valve" or "pressure relief check valve". The purpose of this device is to restrict return flow of fluid in the brake side of the master cylinder so you can "pump up" the brakes in case of a low pedal condition. For this to work the piston has to return faster than the fluid will return. This causes a slight vacuum in the pressure chamber which will in turn draw fluid from the reservoir past the seal lip of the main pressure cup. Fluid slipping past in the forward direction negotiates through half a dozen axial holes in the working end of the piston, then past the thin wave washer that provides space for radial flow, then past the lip of the primary cup. In this manner additional fluid can be drawn into the working chamber to be pushed downstream on the following stroke.
The piston must return freely by spring force only, and it must work with the slight vacuum in the working chamber. That is, if you use your finger to cover and seal the outlet port causing vacuum in the chamber on the return stroke, the piston should still return with spring force only.
The primary cup seal has very little friction or resistance to motion on the return stroke, as there cam be fluid flowing forward around the periphery of this seal during the return stroke (and there usually is). The only time fluid does note flow forward past the seal cup on the return stroke is if you let the pedal up slow enough so the (restricted) return fluid flow from downstream can keep up with motion of the returning piston.
The culprit here is the secondary seal cup being too large on the outside diameter and dragging in the bore. The solution (expedient fix) for the faulty secondary seal is to apply air pressure to the outlet port to return the piston, and cycle it dozens of times (perhaps 100 cycles in some cases) until the seal frees up enough to allow the piston to return with spring force only. This is a PITA, and it should not need to be done, but so far I have found that it always works (eventually with enough persistence).
For a picture illustrating the faulty secondary seal see here:
Repacking kits that I have bought from Moss and V.B. in the past 10 years have had this problem. At this time I do not know of a source for good parts.
|Thanks, all of you, for your help, support, and insights; all I knew about master cylinders when this project started was how to check the fluid level..|
I'll be implementing these latest suggestions once I deal with some of the other usual stuff life throws at us all; it'll probably be a week or so before I can update with the results.
Once again, that worn out phrase; thank you. :)
|Rick, try it in a warmer space. The fluid viscosity will be less and according to Barney, it could alleviate the sec seal problem.|
I don't disagree with anything you say and a secondary seal is a possibility.
What concerns me is that Rick's issues have not been about one MC, but 2 brand new MCs of different make having the same issue. Coincidence?
Look at some of the facts: Rick says they both worked okay on receipt. The clutch side of both worked ok with fluid (probably rules out bore finish and seal quality). Both had same timing issues on brake side. So what is the common factor? Answer is the bench bleeding process giving invalid readings.
It seems strange that so many of us have the AP Caparo MC fitted (Bob West has supplied and fitted many dozens), yet none of us have had any problems. But none of us have done bench bleeding. We have simply fitted the MC and got on with it without any issues.
I wouldn't mind betting that if Rick simply put his MC in the car and bled it like the rest of us he would have one perfectly functioning MC.
|I'll take that bet. If the piston doesn't return while on the bench, it won't work in the car either. Best to get this sorted out before you. start fiddling with fluid in the car.|
|I'll hold the money!|
|Shouldn't Steve have odds in his favour against the Guru?|
|J H Cole|
|Secondary cups are indeed a problem. I had to turn my piston down on a lathe to allow the cup to seat farther down and allow movement. Ordinarily I wouldn't resort to such drastic means but we seem to be stuck with these cups for an definite amount of time, so I modified the good part to help the bad one. If the cup issue is ever remedied by the manufacturer then I'll just replace the piston with an unmodified one. The issue is the same for T-Series rebuild kits, so I've had to do the same modifications there to avoid yet more hours of frustration.|
"Rick says they both worked okay on receipt"....
Not so. They both displayed inordinately long return times out of the box. Initial shortest return time was 7-8 seconds for the Caparo unit, and up to 20 seconds the day after, I assume because the seal(s) swelled a bit soaking in fluid overnight.
The original TRW unit took an even longer (initial) return time right out of the starting gate, and then up to 20 seconds a day or two later.
I only replaced seals once, just recently, on the Caparo unit, and that resulted in not just a long return time, but on top of that, the piston actually sticking about 5/16 inch before reaching the end plate and staying there.
Also - I didn't connect this particular sound with anything until today, but with fluid in the reservoir, after pushing the piston in and releasing, there's this sound as the piston is in it's return stroke, almost unnoticeable; a kind of phut-phut-phut (you'd have to be here..) that, in the context of what Barney just explained, does sound exactly like a seal grabbing, releasing, grabbing, releasing as the spring exerts pressure.
I already have, and will continue as long as my arm holds out, to push the piston in and release without fluid in the reservoir in hopes of wearing any oversize that may be present in the seal(s). If that doesn't get anywhere, I'm entertaining having the bores polished. Any words of caution on bore polishing?
Steve.. Your logic feels absolutely right on: how is it that all of you have not had this problem while I am? It's a mystery to me too.
|Reason that others have not had this problem is because it is a new problem. Lets hope it is limited so a singe production run, and that it will go away sometime in the not too distant future. Meanwhile I have been seeing multiple reports of such problems in the past several weeks (but not before).|
My apologies for harping on in this thread, but I do feel bad about it as it was I who strongly recommended the AP Caparo MC in the first place.
I must have got myself a bit lost in all the posts, but I was under the impression that the MC was ok on receipt. With the apparent fault you appear to be suffering with this one you should not tamper with it any longer, but return it under guarantee for a replacement.
I might be sounding a bit presumptuous here, but I take it that you are in possession of a genuine Caparo MC? The reason I ask is that their MC does not to my knowledge have any exterior differentiating markings (I did not notice any on mine). However, the internal machining is what sets it apart. The bores are so superior to all the others. I had mine on the bench alongside my old 'cheepo' and there was absolutely no comparison. May I ask you who supplied it? Did you pay a lot more for it? The Caparo is about 50% more than the others. In the UK you can expect to pay up to £150 ($230).
Am perversely relieved to hear that some out there are having similar problems and that it may not be a screw-up on my part, and thanks for your input; it shined some light on what looks like the cause of the problem.. :)
Don't sweat it... You can only speak from experience and your input has always been a welcomed read. As does Barney's, Art's, Mike's, Bruce's, Gene's, FRM's, Andy's, and the rest.
The unit is indeed the real McCoy; it has "ap 7/8" on the side with 38183 C underneath, that is, assuming the "ap" is reference to AP Caparo.
Just the thought of throwing away yet more time by returning it and waiting for a replacement makes my stomach turn, but, of course, that would be the right thing to do; it's what makes the manufacturer aware of the problem...on top of agitating the hell out of me. There may be some pushback though since I replaced the original guts with a rebuild kit. I got it from Bob West. It ran me 135 Sterling, or $218 including shipping. There's probably a foreign transaction fee somewhere in there too.
That little guy on my left shoulder keeps whispering to me: Come on, Rick, just take it to the machine shop 5 minutes away and have them polish the bores; if it works, you're home free and screw alerting the manufacturer. I never could make future plans; I always change my mind before I get there. I'll do whatever I do when the time comes.
If your MC was working I would have said that you got really good deal from Bob at that price.
I really don't know why you want to send your MC off to a machine shop to have it polished and pay the cost whilst it is under guarantee and I understand that Bob has said to you to send it back to him.
I had to phone Bob West's anyway and got round to asking James, his mechanic, if they had any problems with the AP Caparo. Absolutely none was the response. Your MC came from a recent batch of 50 of which only 7 now remain. The other 42 are working faultlessly. James has since specifically checked out the MCs either side of yours in the batch and both are spot on - as are the the other 40. Seems very odd.
|Steve, same price I paid. The shipping is about 20 quid.|
Have been meaning to try mine out on the bench. Must get off my a**
For what it's worth I don't know why people find it necessary to bench bleed these things. James told me that they never do it in their workshop. They fit straight from the box, pour in the fluid (silicon) and bleed straight away. Never had any issues. It's what I did and I tend to agree. I don't even remember leaving the fluid to settle for any prolonged length of time.
They are simple items, set up and ready to go. I would have thought that dismantling a brand new item before first use, what ever it is, runs the risk of invalidating warranties. Just be cautious.
|Yes I agree with Steve, no reason to bench fill, test or whatever. I fitted one to my driver six years ago, filled with silicon fluid, bled and drove. has been perfect since. |
Fitted one to another car last year, again with silicon and again without any problems. (After solving an issue with a front calliper).
The AP Caparo stuff is more expensive, but at least you get OEM quality or better.
|Just for whatever it's worth, I'll add my experience with the AP Caparro MC. When I tried to install it, one of the brake pipe fittings would not screw into one of the Caparro female ports. The thread size or pitch was wrong. To fix it: I had to go buy another piece of brake pipe, with the correct end fitting to fit the Caparro, from Autozone. I also bought another brake line that was the next size larger in diameter. |
I cut the old pipe in a convenient, reachable place, and discarded the section going to the Caparro unit. I then cut the new pipe (with the correct end fitting to fit the Caparro port) to length and shape, to replace the discarded section. The old section and the new replacement section now butted end to end.
I then cut a one inch section out of the new larger diameter pipe, and "sleeved" over the 2 sections, then brazed to seal. The sleeve was a perfect, close fit over the 2 sections after lightly sanding the ends of the 2 sections.
After that, the unit worked "as advertised". No problems.
I should have sent it back, but I didn't want to wait, or incur the extra shipping expense.
|Just checked min, Jack. The Moss brake line fits OK.|
I sent the unit back yesterday for exchange.. Bob West was very good about it. Probably be around 3 weeks before the replacement arrives. Shipping wasn't something to shrug off: UPS wanted $159!
Took it to the U.S. Post Office and they charged $60.
|They charged you $60 to mail a master cylinder? Or am I missing something? Flat rate box is less than $10 and no weight limit!|
|Steve, not to the UK for $10!|
|Yep, I missed something! ;)|
This thread was discussed between 03/02/2013 and 27/03/2013
MG MGA index
This thread is from the archive. The Live MG MGA BBS is active now.