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MG MGA - Braking Issue

I have just done a weekend of motoring in lovely warm Spring weather around the New Forest, covering about 260 miles in all. Loads of long traffic queues on the A303 around Stonehenge and later in Lyndhurst. On the plus side the water temperature never got above 190 despite one hour of stop-start with a maximum speed of about 3 mph.. The big issue was that the brake pedal went very soft about 2/3 of the way down to the floorboards, but never failed. The car always stopped very well. I eventually stopped to have a look at the MC. It had overspilled! fluid on the shelf and fluid up to the brim. Before I started on the journey the brake pedal was very firm, just like it always had been after being fully bled. Next morning I went to check the car, in fear of needing a transporter to take it home, I put my foot on the pedal. Totally firm once again and fluid level back down to below the neck.

Today it went about half soft on pedal travel during a 70 mile drive back. I suspect it can only be residual air in the system causing the problem, but why does the pedal feel so firm when cold? I guess I need to give it another good bleed and observe what comes out, but thought I would canvas opinion first. By the way, no leaks from anywhere in the brake and clutch system other than through the MC cap - I have checked.

Steve
Steve Gyles

Hello Steve,
I was going to say that your overspill was probably due to heat expansion of the discs pushing the calliper pistons back further than on a short journey with no heat being generated but that is a hell of a lot of movement/displacement.

A sticking master cylinder piston would give a soft feel because there is no initial resistance to displace the piston - just mechanical return spring feel. After the scary soft feel takes up the slack, normal brake pressure is applied. I guess you did not smell hot pads? When you got a firm pedal next morning, the piston had moved back to the normal 'rest' position. My first item would be to check the free movement of the M/Cyl piston and possibly replace those and the calliper seals.

regards
Colin
Colin Manley

Steve, when the pedal is soft does it become hard again if you pump it up? If so I suspect you've got air in the system - are you running a servo?
J H Cole

John

No. It remains soft. When I looked under the bonnet I was able to push the operating rod 2/3 distance before any resistance, as if the piston was not returning. But the MC was totally full to the brim and had also overspilt. Before I started out the fluid level was below the neck. No servo.

Steve
Steve Gyles

Steve

Two comments.

Firstly if you haven't done it recently it may be an idea to change the fluid.

Secondly in a company Cortina in the 80s I lost brakes completely and next morning the brakes were back to normal and I never had another problem. This incident took place on an alpine descent (not an extreme one and driven at normal family car speeds) and I always assumed I boiled air out of the fluid. On the other hand I can't see how you could have got the fluid this hot, but the common factor is the recovery of the pedal pressure.

I think the second option is a long shot but it does explain the recovery and if you had something sticking it may just be a possibility.

Good luck.

Paul
P M Dean

Just been to inspect the system now that it has rested for 18 hours. The fluid is at exactly the same level as before the weekend, that is despite the vented overspill. The pedal did seem a little soft, but pumping made no difference. Horizontal movement (slack) of the operating rod was about 15mm (guess). However, while writing this response I went out to the car to take an accurate measurement and found it had tightened up to about 1mm and the pedal was back to absolutely firm. The clutch side has been perfect throughout.

It all seems a bit odd to me. The system has given me no trouble at all in the last 4 years. The only thing I had done at all different in the long traffic queue when the problem arose was to keep that bilge pump thing running. First time I had ever used it and only switched it on out of mild interest and boredom. I am still not convinced it made any difference whatsoever to the carbs cooling. Perhaps instead it blew the hot air around the compartment and oven fan cooked the MC!!!!! It does have a lovely roasted chicken look to the main casing.

Steve
Steve Gyles

Further to my last, the attached photo shows the well basted and browned MC body. It was standard metal last week, as it had been for the previous 4 years. It does not seem to be rust, just baked on fluid. Interestingly it has not affected the upper body extension.

In the long traffic queue it was the clutch I was operating all the time and I wonder if it was that side of the circuit that generated the heat? I hardly touched the hydraulic brakes during that period, mainly just using the hand brake or the odd dab of light brake as and when.

Steve

Steve Gyles

Steve, how much air volume do you think is left in the MC above the fluid? ie what was the volume change causing the overflow. This is a strange one indeed!
Art Pearse

Steve - I'm wondering when you last bled the brakes. If the brakes haven't been bled they will have drawn in water through the slave cylinder seals and this can boil. Steam isn't any good as a brake fluid, which is one of the reasons for bleeding them. Hence the soft pedal. This steam pressure will also blow the fluid back to the M/C and may have caused the brakes to rub and get hot too?
Your bilge blower is fine as your clutch didn't suffer any problems. The weather is still very cool yet for them bilge blower benefits.
I was out in mine too yesterday, (Arundel) the blower wasn't needed - admittedly I didn't have any jams. Running like dream with the richer needles...
Pete
P N Tipping

Pete

What you are saying would be more applicable to glycol brake fluid which can absorb up to 12% water by volume. However, mine is silicon which does not absorb it. Because of its properties silicon brake fluid does not need changing with the same regularity; some owners have kept the same fluid in for 20 years or more. I have not done a specific fluid change since I rebuilt the car in 1996, although it has been bled through a number of times when, for instance, I changed over to disc brakes and later fitted the Caparo AP master cylinder 4 years ago.

I am quite happy with what I am going to do over the next few days - MC inspection and bleeding. I don't believe I have any problems down at the wheels. Front wheels release and spin freely as soon as the pedal is released. The car brakes very firmly as always and in a straight line etc.

I am quite relieved that I have the silicon fluid, otherwise my bulkhead would be stripped by now!

My quips about the blower and fan oven effect were all a bit tongue in cheek, although I do genuinely have my doubts about its value in my car as I have never had overheating issues. For example yesterday I sat at 75 to 80 (just keeping up with other M3 traffic!) for mile on end and never moved above 175. Earlier, in the hour of queuing it stabilised at 190. I then put the bilge pump on and saw no change on the gauge nor felt any difference in throttle response. The only noticeable happening was sudden concern from the wife about the strange whirring noise that started from the engine area (she was nodding off at the time in the warm sun).

Steve
Steve Gyles

I think Pete may have the reason - water. It doesn't need to be absorbed in the fluid, drops of free water will boil just as easily, in fact more so than if diluted. If it boils, then you only need a little over 100 deg C to generate the steam as you release brake pressure.
If I were you, I would change it out.
Of course when brakes are applied, you need a higher temp to boil. The steam will condense if you push hard enough, but I expect that explains the sponge and the overflow.
Art Pearse

Art

No. I don't accept the water theory. The fluid was warm but not that hot when I looked. I was able to touch it quite ok.

Steve
Steve Gyles

It only needs to be hot where the water is, so a drop in the calipers could do it.
Art Pearse

I see what you are saying Art and I will try to keep an open mind on it when I take it apart. I am just having difficulty seeing how water can get into silicon fluid. It was developed specifically in the USA to get rid of that issue in military vehicles and proved brilliantly successful.

Steve
Steve Gyles

Surely it is not inconceivable that some minute amount of wetness could get into the fluid around a piston/caliper over a period, and then it can boil. I would certainly do a complete fluid change after nearly 20 years.

Paul
P M Dean

I hadn't realised / forgotten you had silicon fluid Steve and agree with your thinking of course. Its just that what you describe sounds like boiling water / steam in a brake cylinder(s) causing expansion and thus the soft pedal you describe with the firming up again when cold. How water gets in, not a clue, but it seems the only thing that makes sense to me. After 4 years can you remember how to bleed brakes OK???
The Bilge Blower - is nothing to do with the radiator's water temperature and is useless when driving on the open road. It's for use when you start getting vapour-lock in a traffic jam, especially useful when you hit a jam immediately after high speed running and those very hot days. If it helps, as a guide shall I say - DO NOT SWITCH THE BLOWER ON UNTIL STATIONARY AND VAPOUR-LOCK OCCURS..? The blower restores the tick over to normal and the car is still drivable.
Pete
P N Tipping

Steve, Silicone fluid still needs to be bled periodically to remove contaminents such as water, dirt etc. It also seems to expand more with heat and ambient temperatures, than glycol based fluids. Silicone fluid does not absorb water as DOT3 does, but water does enter the system, and does have to be purged.

I would bleed the system as normal and see if this solves your braking issues.
CR Tyrell

Steve

An additional thought on this adding to what I said last night (and speaking as en ex Chemical Engineer, up market plumber as other engineering professions called us!)

I don't know the specific gravity of silicone fluid but it if it is heavier than water it would over time migrate to the lowest point in the system, i.e. pistons/calipers. This would tally with being a beginning of season issue. On the other hand, even if it is not heavier than water, these are the likely entry points of water hence another reason for the water being in these areas. Put this together with the fact that the brakes are the only place likely to get hot enough to create boiling you have a soft pedal that will get better when the water goes back to liquid form as it cools. (I guess that if a brake pipe touched the exhaust this could cause it but this seems very unlikely with pipe routing.)

Following this logic of the water being at the brakes a quick bleed would solve the problem in the short term but it would be likely to reappear over time. You really need to schedule a change of ALL seals and a fluid change.

Good luck.

Paul

P M Dean

Thanks for the comments to date. Originally I was just going to bleed the system while looking for air bubbles, topping up with replacement fluid as I went. I will amend that now to draining the system, so that I can observe the contents at leisure. With luck I will still be able to look for any air bubbles during the initial 'opening the taps' while I push the fluid through with Eeezibleed (bottle empty).

If there is water in the system (which I doubt but am trying to keep open minded) there is a chance I will be able to see it in the collection bottle as silicon is immiscible with water. I need to check whether water floats or sinks! I am sure someone will tell me before I get round to doing a check.

I have just had another look at the MC this morning. Interestingly the clutch operating rod has now gone tight whereas the brake side has about the normal 1mm of slack. The problem I experienced with the brakes started during the phase of very heavy clutch use in queued traffic and extremely little brake. Furthermore I am naturally quite light on the brakes so I don't believe I had overheated the brake side of things when the problem manifested itself. Could this be one of those 'referred' issues, similar to fuel/electrics symptoms getting crossed over? Did the clutch piston in the MC stir up the fluid into an aerated mix which then got shared with the brake piston operation? The clutch operation did get a little juddery at the same time.

Steve
Steve Gyles

Steve

1. The hydraulic fluid will reach the ambient under-bonnet temperature in stop-start traffic, and any expansion is likely to be from that rather than from the cylinders
2. The coefficient of expansion due to temperature increase can't be that big on a relatively small amount of fluid
3. As far as I remember you have a relatively new caparo MC.
4. The fact that you were in heavy clutch use at the time the problem emerged points to a clutch oriented issue rather than a brake system problem
5. A few years ago I had similar issues with a soft clutch pedal which turned out to be seals in the clutch MC. But as your MC is relatively new, I believe that could be ruled out. The brakes worked fine until a pin hole on a brake line caused a gradual fluid loss ( the pin hole was caused by vibration of the transverse pipe under the engine against its securing tab)
6. As others have pointed out Si fluid should still be bled periodically, but you would need a hell of a lot of water in it to cause severe problems as you describe, and an abient engine compartment temp of over 100c to make that water boil and produce steam in the hydraulics. I cannot believe that the ambient temp went that high. Or that you have enough water in the fluid to get such a head of steam.

So a few questions arise

A. Do you have a vacuum booster? Thinking is if you do, maybe it has failed in a way to pressurize the MC
B. How full was the MC when you started, and how much fluid do you think has flowed out
C. After bleeding, how much water is in the fluid, and where has it come from?

But otherwise I am as puzzled by this as you appear to be!
Dominic Clancy

Thanks for your thoughts Dominic. No, I don't have a vacuum booster. Yes, I have had the Caparo for 4 years and am delighted with its performance to date. I am prepared to wager that it is not directly a factor/cause in this happening. Like you suggest, I am inclining towards air in the clutch side piping, manifesting itself across to the brakes. I have not bled the clutch side for a good many years, just the brake lines. In fact, when I swapped the MC to the Caparo I may not even have bled that side since it appeared to operate fully after I had filled the MC and allowed it all to settle for a few hours. May be that is my problem. Unlike the brakes you don't hit a hydraulic lock when pressure is applied on the pedal. The clutch either works or it doesn't. For the past 4 years it has worked fine, and as I type it still does.

In the recent service I checked the fluid level and it was about 0.5 cm below the bottom of the neck. It is now 1 cm, so I lost perhaps 0.5 cm depth of the inside area of the MC extension.

I am waiting for a new supply of fluid to arrive before I get down to business and do the work in one go.

Steve
Steve Gyles

Couple of comments. The expansion rate of the fluid itself cannot account for such an expansion. However 0.1 cc of water turns into 100cc of steam roughly at ambient pressure (brakes released), so you do not need a lot of water at all. Actually, the water would be safer if it were absorbed in the brake fluid!!
Art Pearse

Not necessarily so Art. The following is an extract of an article taken from the MGCC Safety Fast magazine:

"Foremost among the problems of conventional glycol fluids, is their hygroscopic properties - when exposed to air, glycols absorb up to 12% water by volume. The water lowers the boiling point. Under normal driving conditions, a car, driven daily, or even weekly, will heat up the brake fluid and evaporate a significant amount of the absorbed water. At higher percentages of water the brake cylinders corrode rapidly leading to early brake failure (probably due to electrolytic action as the mixture conducts more). This occurs in cars that have not been driven for several months. On being driven, the rust or corrosion soon causes one or more seals to fail."

Steve
Steve Gyles

Steve,
check the calipers, i.e. remove the pistons. You might find water or rust in there. Water is heavier than Si.
How I know? been there...
Siggi
Siggi

So if I'm following this thread correctly, are the water advocates reasoning that entrapped water within the brake calipers has boiled due to high temperature from the brake pad and disc, pressurized the brake fluid and forced fluid back into the reservoir and out of the cap? This water I presume has been absorbed by the free surface in the reservoir - if it were to get past the caliper seals there would be tell tale signs of fluid leak - or the water was always in the fluid when the calipers were set up. It follows that a quick test would be to bleed some fluid from the calipers and carefully test for water. The chemists among us might be able to suggest a tracer to identify the presence of water within silicone otherwise it could be difficult to tell.
Steve, I do hope you get to the bottom of this one, it deserves a good answer given that so many of the problems raised on the site seem to 'fade away'.
Just thought of a water test - why not heat a small sample of fluid to just above 100 degrees and watch for bubbles or better still stretch some cling film over the container and see if it's pressurized from the vapour.
J H Cole

Here's my theory - little bit of water in the caliper(s). Steve tromps on the brakes, calipers heat up to >100C. Water in calipers gets to same temp, but cannot boil as Steve still has pressure on the pedal. Steve releases brakes, pressure in the caliper goes low and the water boils. Vapour generated pushes out a volume of fluid back to the MC and it overflows. The vapour bubble does not necessarily reach the MC, staying in the caliper where it condenses as the caliper cools. It is still there!
Since it does not mix with silicone fluid, it is segregated as a drop, either top or bottom of the caliper, depending on density.
The clutch thing is a red herring.

Art Pearse

I like the theory Art. Siggi is correct in that water is heavier. I just added a drop to some fluid. It is easily distinguishable. It breaks down into minuscule droplets when shaken but remains very obvious in the fluid. I should have some time in the morning to drain the system and all may start to become clear. Still not convinced about it being water though.

Steve
Steve Gyles

Steve

If you can see the water that is fine and conclusive but if you can't see the water that isn't conclusive. 1cc of vapour in the system would certainly create a very soft pedal if you think about how much fluid the MC moves. 1cc of vapour only means 0.001cc of liquid water (see Art's correct comment posted at 1706 UK time), that is a hundredth of a drop of water so you may not see it.

Art's explanation sounds reasonable. I am not sure what the fluid pressure gets to in a good brake application but one bit of data is that doubling atmospheric pressure only puts the boiling point of water up to 120c.

Paul

PS
Your MC looks quite attractive in bronze. Is it tacky or dry? Were the pipes and pushrods already bronze or have they changed as well?
P M Dean

Paul

The MC bronze is like paint. I could not have painted it more evenly if I had tried. It is hard and not tacky. Just a bit damp with a coating of silicon. The pipes are standard copper. The colour of the pushrods etc is more down to the camera flash.

I feel confident I will spot any water. Even the smallest particle was clearly visible when I shook the mix.

Every one is going on about water, but I remain sceptical. Yes, with glycol fluid it would be a very high probability as it absorbs up to 12% quite naturally, but silicon does not.

Interesting, re changing silicon fluid periodically, the instructions label says it can be left indefinitely.

Steve
Steve Gyles

Steve

I suspect that you will replace the fluid and everything will be fine and we will never know quite know what happened.

My reasoning for water is that all discussions seem to accept that there is gas in your system as the only real explanation for soft pedal. There are only 2 really possible gases, i.e. air and water vapour. If air was the problem it is difficult to see how the problem would come and go, whereas with water changing from liquid to gas state you could get the changing situation. I agree the problem would be far more likely, and probably worse, with hygroscopic standard brake fluid but this doesn't exclude a small amount of water being in the system albeit unabsorbed.

Good luck. I am currently struggling with a more mundane issue of stopping my exhaust touching the chassis cross member since I have fitted my early B engine!

Paul

P M Dean

I have just bled the entire system through. The first thing to say is there was absolutely no sign of water anywhere! There was a small amount of air in both front callipers but very little and probably of little consequence. The two rear drums were crystal clear. However, there was a moderate amount of air in the clutch which could account for the symptoms. It is of course possible that the hydraulic system more or less sorted itself out during the run, purging the air in the process. This could perhaps accounts for the overflow as the air expanded and blew itself back into the MC, taking fluid out with it. Interestingly The bonnet (hood) exterior paintwork immediately above the MC shows signs of heating, so the MC must have got quite hot at some stage. Makes me wonder about the value of the MC extension being so close to the bonnet underside.

I am now going to adjust the clutch push rod and do some road tests to see how it all feels.

Steve
Steve Gyles

I think I have found the cause. I could not release the clutch pushrod in the MC. I have taken the MC out and examined it on the bench. The brake push rod is 7.8mm diameter and is a loose fit into the recess inside the piston. The clutch push rod is 7.9mm diameter and is a very tight fit into the piston. In fact it is solidly attached. The result is that the piston is additionally dragged backwards by the clutch pedal return spring on clutch release. Also, because the rod and piston are fixed with no movement between the two the piston is being pushed and pulled slightly off line because of the slight pivoting arc of the clutch lever. This has accentuated seal wear and caused a build up of black gung on the piston body.

Odd that the two rods are of a different diameter. This particular problem was not apparent with the old MC. I can only assume that the inside piston machining spec with the Caparo is slightly different. I am also bemused as to why the rods are slightly different in diameter, but that is what was there when I bought the car. Interesting that they are not a pair. The rogue one does not have the hexagon shoulders for holding the rod while the lock nut is tightened. The lock nut is also different.

Perhaps someone can put a scenario together for me now that accounts for the overspill.

Steve
Steve Gyles

Just to clarify the push rod difference, the issue is not directly the slight difference in diameter (it still slides into the hole), but the altered diameter of the rounded end. The bore hole in the piston is rounded at the end to receive the rounded end of the push rod, thus centralising the rod and allowing it to pivot. As the rounded end of the oversize rod is to a slightly different profile/diameter it jams in the hemispheric recess. I hope that makes it clear.

New parts and seals arriving tomorrow. The bronze coating has polished off. Good as new. Also no apparent damage to the clutch cylinder wall, nor the piston.

Steve
Steve Gyles

Steve, I had to grind the ends of my rods a little to fit the Caparo MC
Art Pearse

That's interesting Art. My presumably original rod is fine. Glad you caught it early! May be something for others to check. There is usually something to learn from these incidents.

Steve
Steve Gyles

Steve, this clutch thing cannot be the cause of the brake softness.
Art Pearse

Art

That's why I asked for someone to write me a scenario. I can only assume that the weird clutch operation was aerating the fluid in the MC. This would then get into the brake side and soften the feel. Left overnight the air would gradually bubble out of the system.

Steve
Steve Gyles

OK, here's another scenario!
The MC piston is locked on to the clutch pushrod.
When the clutch is released, the piston is forcibly retracted by the pedal spring. As it is drawn back the seal relaxes a bit and air enters, and somehow this air gets into the M/C reservoir. Silicone fluid I'm told tends to stabilize air bubbles a long time before they clear.
To support this, your MC seal must be getting old.
Art Pearse

Art

I was thinking something along those lines. As I mentioned above the rigid nature of the rod and piston causes the piston to operate slightly off line during its travel, just as if the piston and conrod were seized together in an engine. This is supported by some seal gung on the piston body. The brake seal and piston show nothing of this wear and gung. New seals just arrived.

Steve
Steve Gyles

Art's theory sounds good but where did the heat come from?

Paul
P M Dean

Paul

As I said earlier, it's that bilge blower doing a bit of fan oven roasting!!! Everyone sang the praises of it last year, but you never get something for nothing in this world; always side effects. Must check to see if I have steam coming out of the windscreen washers.

Seriously though, I have no idea. It seems odd to me unless the exaggerated 'suction' on the clutch side caused hotter than normal fluid to migrate to the MC.

Steve
Steve Gyles

Steve - perhaps the drag on the clutch piston happening very frequently in heavy traffic caused enough friction to heat up the fluid.
Cam Cunningham

I have just removed the brake piston from the MC and look what I found dislodged (possibly end on) at the bottom of the cylinder. The washer is permanently disfigured as can be seen in the photo. Could account for a lot! It must have been like this from the manufacturer's assembly. I know I have sung the praises of the Caparo AP machining of the bores etc, but looks like a bit of human hand shortcoming somewhere along the line!

Steve

Steve Gyles

Steve, what exactly does that washer do?
Art Pearse

Art

Not a lot by the looks of it! It has not caused me any obvious issues in 4 years until last weekend. It will not have allowed the spring to seat properly with the return restrictor. I think we need someone like Barney to explain the consequences.

Steve
Steve Gyles

The small rubber cup in the center of the "non-return valve" is the forward flow check valve. This is the bit that allows you to pump up the brakes. The flat rubber washer in conjunction with the flat side of the non-return valve metal shell is the low pressure return relief valve. This should retain about 8 to 12 psi residual pressure in the brake hydraulic circuit when the pedal is released. This is also part of the pump up function.

If the piston return spring is too strong, this will retain too much residual pressure and the brakes will drag and overheat.

If the rubber washer is missing or dislodged so it doesn't seal, then it will not hold residual pressure, and the pump-up function may not work. This may not matter when the brakes are properly adjusted and work with one pedal stroke. But if brake shoes are out of adjustment it makes for long pedal stroke, and then pump-up doesn't work.
Barney Gaylord

Thanks Barney. Would I therefore be correct in saying that the fluid flow-back into the MC would be totally unrestricted, perhaps allowing faster transmission of heat back through the fluid into the MC?

Steve
Steve Gyles

Unrestricted yes, but nothing to do with transmission of heat.
Barney Gaylord

On the basis that a picture is worth....I hope the sketch illustrates the issue here showing that the system seals itself to about 8 psi under the spring force. Way back in this thread Steve said I think that he could not 'pump up' his brakes. A distorted washer would explain this. On the question of spring strength has there ever been any comment on testing the spring for the correct stiffness?

J H Cole

The anti-return valve covers the full bore size (generally speaking). 7/8 inch bore is 0.61 sq-in. To regulate 8-psi back pressure the spring force would need to be 0.61x8 = 5.5 lb-force when the piston is returned to rest position.

Some recent issue new master cylinders seem to regulate back pressure at about 12-psi, meaning the spring force may be more like 8.25 lb. This will cause the brake to drag and heat up while driving.
Barney Gaylord

Great discussion...thanks for posting your findings, Steve.
Gene Gillam

So much has been written about binding brakes over the years but it seems with less comment on spring strength being the culprit. Is there a spec on the spring such as length and stiffness that could be checked?
J H Cole

I was wondering the same after reading what Barney has said. Is there a simple check for us amateur engineers with limited equipment in the garage.

Steve
Steve Gyles

I have 1/2 dozen of these springs acquired as a job lot many years ago and I've tested them DIY fashion by pressing each down a fixed distance on a kitchen digital scale and reading the force required. Although very inaccurate I can tell that there's possibly around 15% variation in spring stiffness. They seem to be about 80 mm long (3.15") and there's up to 3 mm variation in length. Not sure if these results can be extrapolated to MC pressure but there could be a pressure variation of 15%x8 psi= +- 1.2psi This does not seem so bad but these are old springs and as Barney suggests the danger is with new stiffer springs.
J H Cole

MC reassembled with new seals. Complete bleed. All the pedals now much firmer and the system is fine. In summary this thread highlighted the following issues:

1. Brake cylinder washer not seated. It was probably lying at an angle against the cylinder wall.

2. Non standard clutch push rod was jammed in the end of the piston, probably aggravating clutch release.

3. Small amount of air was in the system, but no where near enough to prevent operation of the hydraulics.

4. Water does not seem to get into silicon systems (my fluid been in for 17 years). If it does it is clearly visible and sinks to the bottom.

5. Caparo AP MC may have a slightly different machined profile inside the piston bore where the push rod rests. Owners converting to this brand should check for no interference with the push rod.

Finally, one new point, my right hand drive clutch lever that I bought when I converted LHD to RHD has a different at rest profile (see photo). The replacement push rod just has enough screw adjustment to take up this difference.

Steve

Steve Gyles

Not noticed before, but those push rods are not parallel. I presume they should be? It was only looking at the photo that it became apparent. Often wondered why I had to put in extra shim washers to prevent the clevis pins fouling. I will remove the rubber boot tomorrow to look at the pedal shaft spacers etc.


Steve
Steve Gyles

Steve, Make sure that the non-parallel is not just camera lens parallax. glad you have solved the problem.
CR Tyrell

I have just been speaking with Bob West and think I have solved the non-Parallel problem. Incorrect (too thin) washer fitted between the 2 pedals.

While I was chatting, it seems that Art and I are by no means the only ones to have push rods stuck in the pistons on Caparo MCs. Worth checking.

Steve
Steve Gyles

Steve I am rebuilding my master cyl and was wondering if you had a simple method (TRICK) to get the piston and the seal into the bore without damage. Thanks in advance Bill
Bill Mason

Bill

Me and the hydraulics system do not have a good reputation!!

I made sure the seals and cylinder bores were lubricated and then just pushed. The lip of the bore is chamfered which helps. Yes, it was a hard initial push but in they went. A few pushes against the spring and they settled in and operated smoothly.

Steve
Steve Gyles

Hi everyone for clarity can someone please confirm the correct part number for master cylinder for MGA with disc brakes (not de-luxe or Twin Cam).
I have lost my reference book and cannot recall if the correct cylinder has the smaller bore size (3/4") and is GMC 112.

Many thanks

Mark
Mark Dollimore

7/8" is correct bore.
Art Pearse

Thanks Steve After all these years I should have know that a little lubrication always helps. The seals slipped in with no problem. Bill
Bill Mason

Well done Bill.

I have just received from Bob West the 'correct' washer that fits between the 2 pedals. For future reference, just in case anyone is interested, it is 6mm thick. The supposedly correct washer that came in my kit back in 1996 is 2mm thick. That accounts for the non parallel push rods.

Steve
Steve Gyles

Art

I've looked up the AP Caparo catalogue and they advise the 3/4" M/C for disc brakes - I'm confused.

Mark
Mark Dollimore

Mark, I believe the MG midget uses the 3/4.
Original M/C for the A is 7/8 (Lockheed)
Art Pearse

Finally all back together how it should be with the push rods parallel. The repro clutch pedal sits at rest fractionally further back as can be seen in the photo. I could have welded some metal onto the 'stop' area of the pedal shaft, but this would have put the brake and clutch pedals at different heights and why change what I have got used to? instead, to give me more available adjustment with the push rod I welded extra length into the push rod and cleaned it up on the lathe.

One final point, I noticed when I took the assembly apart that I had originally installed the seal plate cover with the lip pointing down. It should be up. I guess I did it that way back in 1997 because the seal fitted conveniently inside the lip. Chatting with Bob West he says he often finds cars with the seal plate that way round. - just a minor detail point.

Steve

Steve Gyles

This thread was discussed between 13/04/2014 and 28/04/2014

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