Master Cylinder rebuild.

[Forumadmin]

After the brake failure outside the Drivers' Lounge at Goodwood, Scott and I spent 5 days investigating. There are some things to learn from this saga.
On the Thursday night we took off the cylinder in the fading light. It seemed like the seal was loose on the piston which did not really explain why there was total loss suddenly with no sign previously. The pressure did come up after 5 vigorous and rapid pumps.
Luckily I was carrying a new kit so this was put in. The piston did have some wear and the piston had what looked like a circumferential crack, but that might have been induced when trying to undo the locknut on the makeshift bench on the Glamcabs site in the semi-darkness. Anyhow the master was refitted but we could not get any pressure. Next day was spent locating fluid and a bleed tube. Eventually after much flushing they seemed to be working. I went around the perimeter circuit applying the brakes many times and all seemed OK. Then the Jav was pressed into service taxiing. It was Ok delivering clients but on the way back developed the same fault with total loss but eventually some pressure through pumping. It did not leak away, just needed pumping to get some pressure in the first place. However, it was not consistent and sometimes even pumping did not work and the handbrake had to be used. Luckily I was going through the estate grounds when this happened. I returned very carefully to the taxi rank and started phoning around! Ian Roxburg came up trumps with a rebuilt cylinder and Nigel Snelling Colyer brought it to site on Saturday morning. On it went but no end of help from visiting Jowett owners could get a consistent pressure. Eventually on Sunday morning after a thorough flush we seemed to get a hard pedal. The car did a full afternoon's work with no problems. It also made it the 40 miles along twisting lanes but once on the motorway poor Scott who was driving had brake failure again at 65 mph in heavy traffic in the dark. No harm done except to Scott's heart rate.

So next day it was under the car. First we eliminated the servo by bypassing it with a pipe pinched off Jack's Javelin. To bleed we used a cap fed from air pressure in a tyre. Now this showed a problem with fluid coming from the rubber pipe in the low pressure feed. The pipe had obviously been on there 60 years hidden inside the chassis. It was disintegrating. A new pipe was fitted and the system flushed and bled. Lots of pressure. But the problem returned after a few applications of the brakes. Observing below Scott noticed the piston was not returning. I was not able to put a spring on the piston like I had done on the SC; so instead just put the other mod that I had done on the Sc. That is put two clevis pins in the long slot so that the returning brake pedal forces the piston back. Seemed good, so we reconnected the servo, flushed and bled again. Then took for a test drive and all seemed OK.

A few days later I took the Jav to a funeral in London and back to the wake.. Lots of braking and naturally I was a little wary and gave myself more than normal room to brake, quite difficult to do in London traffic! No problems.

A few days later I dissembled the original cylinder to discover bits of rubber in it. Could one of these have blocked the return bleed hole? I do not think so. Some of the rubber had coated the piston in a few places and this seemed to retard the seal from returning. This could be a contributory cause.

Were the new seals too tight on the piston? Possibly. I put new seals and a new piston into the cylinder and did a bench test. Sometimes the piston did not return. Jack suggested it was a less than compliant end boot. This was removed and the piston consistently returned. So a new concertina type was fitted which had a tie wrap on the large end. Once again the piston did not return after a few initial stokes when it did. Ah hah. The seal was now so good at both ends the air pressure in the boot was stopping the piston returning. So I pierced the boot and the piston now consistently returned.

This saga may not be over. But until the Rover is off the lift I cannot move to the next stage and replace Ian’s cylinder. What it does show is that a non-returning piston is very serious. So unless anyone can say why such a long slot is required in the pull rod I will continue to have a positive way of returning the piston at the pedal by closing the gap in rod. Could the slot be a relic of the hydro mech system? It also shows that the little bit of rubber pipe should be renewed frequently (well perhaps every 30 years). Care also needs to be paid to the fitting and un-sealing of the boot.

PS.... I am not quite sure who the relevant expert is on this subject. But please take heed and make your own judgements when rebuilding cylinders, fitting them if built by others or checking the braking system before using the car.

[Keith Andrews]

Im sry...this is a little blunt.
And this comes from my hot rodding background...Not british 'rover ' hot rod but American steel V8 big weight big power...
In my books there is not such thing as a temp fix , or any reason why a cae is on the road... or race track , where there is the slightese suspision of ....or put another waay, 100% failt in the braking system..
Anything short of this is serious danger to inocent lives...and bring very bad press to the classic car hobby when things go baddly wrong..

Just because brakes pump up after bleeding, doesnt mean they are ok....from the discriptions above, a fade test would have shown up ...
Did anyone at any stage, pump up the brakes, then press really hard, nearly ripping the seat out of its mounts( which should not be possible) holding for a good 15/ 20 secs....there should be nill drop of .
Then rease the foot pressure marginally, but not enough to release the shoe pressures, and reapply the pressure...once again the pedal should not go the slightest bit further down than previous.
The slightest failure of eitrher of these .. even thu the pedal pumps up after bleeding and pedal 'feels' good, is a failure and the car should not be on the road... or track.

As to replacing and using a MC that even has a suspect defect in a bore is crazy...in NZ one leaves ones self open to a mansaulter charge, that even if one gets off , solicitor fees will loose your car home everything.
Re kitting with out a hone and with out measuring the bore... same.

As to 'rebuilding' espec on old classic cars...we dont do it on new car in the workshop ... to do it on cylinders that have most proberly been honed out several times in their life...had poor brake maintance, contaminated fliuds/ hydrocloic acid laying in them...is just not on...
All the workshops I know will refuse to hone and re kit old brake components...because with modern communications , accident investigations brake faulure due to 'back yard' honing and kitting HAD a high instance of failure, publicity, expensive legal issues, destruction of the workshop reputation in the media.
What to rebuild a MC, slave , whatever.. send it away to machined, stainless sleeved...THAT is a rebuild, and anything short of that is back yard accident waiting for a death.
Brake failure is not an option.

I am not quite sure who the relevant expert is on this subject. But please take heed and make your own judgements when rebuilding cylinders, fitting them if built by others or checking the braking system before using the car.

This statement somes up lesson learn very well

[Keith Clements]

Well done KA. You seem to have missed some of the points and perhaps shown your lack of understanding of the Javelin Master cylinder. It does not have a bore which can be honed and does not need sleeving. It has a piston that is guided by an aluminium ring (or plastic if using the new NZ mod). Perhaps you can tell me where in NZ you get Javelin master cylinders professionally rebuilt and thus absolve yourself of any legal implications . I prefer to trust my own skills in these matters having done so much competition with Jowetts. I bought my rebuild kits from JCC NZ. Yes we were satisfied the cylinder was working before taking on the road. What this saga shows is 1. a rubber pipe disintegrating from the inside might have caused a sticky cylinder, 2. A well fitting rubber boot might prevent return of the cylinder. 3. Rather than relying on the internal spring in the cylinder some extra means of returning the cylinder would be safer. This can either be an extra spring on the piston rod or some closing of the gap in the attachment to the brake pedal whilst leaving the play to allow the piston to fully retract.

Whilst you describe tests to do on brakes, not all systems react in exactly the same way. It would be interesting to do your tests on a dozen assembled Jowetts and feel the difference. In this particular case those tests may not have shown the probem.

I hope that those rebuilding, or having rebuilt master cylinders from someone else, will check that the piston returns smoothly each and every time from full extension without any grab. Turning the piston through quarter of a turn and doing a dozen pulls might also increase confidence in its operation. Also 'renew that bit of rubber pipe ' should be on everyones to do list. They might also consider adding extra pull back on the piston or putting an air hole in the boot, but that is their choice and I am not acting a technical expert on that!

I have one further hypothesis on the failure and that is a weakened return spring inside the cylinder. I performed a simple test but really need to try with a spring tension guage. This is highly unlikely as the same problem occured on two cylinders. We have also checked the freedom of the cylinder to the chassis and loosened the bolt. There may have been more than one problem here of course.

[Keith Andrews]

My post was intended as a over veiw of attitudes to brakes be it Javelin or a mini, or a old jag....I did not at any piont mention Javelin
And yes that is one thing that has always impressed me at the NZ shed, the attitude to wards brakes....the insistant of many members to not hone old bores, but have them re slieved when new units cant be purchased...
I assume here that like NZ members, UK members also own other classic/ old cars.

What this saga shows is 1. a rubber pipe disintegrating from the inside might have caused a sticky cylinder, 2. A well fitting rubber boot might prevent return of the cylinder. 3. Rather than relying on the internal spring in the cylinder some extra means of returning the cylinder would be safer.

As I said above, brakes should be servived and maintance at regular interals... how in that case does a rubber pipe get to the perished let alone disintergeting? A well fitting boot, like all parts that move thru rubber... like sliders on disc brakes, these should be lubed with copper brake grease anyway... and interal spring , maybe this then should be put back to the NZ club for consideration...are these orginal used springs that may have lost tension, or new springs re made to the tension of an old spring , Or are new springs , but the other issues as suggested be the problem... I do not know nor wish to specualate .. but it is matter that should be followed up with the NZ club just in case.

Whilst you describe tests to do on brakes, not all systems react in exactly the same way. It would be interesting to do your tests on a dozen assembled Jowetts and feel the difference. In this particular case those tests may not have shown the probem.

These are NOT MY tests.. they are simple std workshop tests after ANY brake work is done and brakes re adjusted up.
And I ommitted ... check All wheels spin freely, ie a check that cylinders.. including MC, return and dont cause drag...
And that there is not a brake hose that has delaminated from the inside acting like a valve.
As to interesting to do the checks on assembled javlens.....If on the road those checks, plus checks for grabbing / lock up on wheels, braking efficiency should all have been done regardless....maybe if they and regular maintance as described had been this thread would not exist... or rather more, which was intended, a support/informational post to what I believe was your intention... not to take brakes so lightly.

It does come back to my post, thu maybe a bit blunt, and I take brakes very seriously, is more pionted at an across the board general attitude...and too many people think that just because a brake system pumps up it is in good order.

[Forumadmin]

Quite frankly I did not know that rubber tube existed mainly because it is not on a Jup and I have never rebuilt a Jav. It is well out of sight and if it were not for the pressurised bleed system we may not have found the problem. It is in the parts manual, but not very clear. It would be interesting to ask how many people have renewed that pipe in the last 60 years.

Since the rebuild parts came from NZ without any air bleed hole in the bellows I suspect that this problem may not have been detected. If indeed it is thought to be a problem. Perhaps you could ask the guys next time you speak to them and get them to respond to this thread.

As far as the internal springs goes, I doubt if we know what the original tension should have been. I have about six I can try so will see if I can detect a difference. One answer is to fit a stronger internal spring, but it is easier on a Jup to fit an external one. Until I get the car on the lift I cannot see how to do it on the Jav.

There is still the outstanding question about why there is such a long slot in the connecting rod which stops you using the pedal to help return the piston.

It is possible the pipe work or something else is preventing the unit from rotating slightly when the brake is applied thus binding the piston. Hopefully I do not need to say that Scott and I did check for free movement, but you never know with Jowetts. They have a mind of their own.

Another possibility is the new seals/pistons need 'running in' or are too tight on the return stroke; but that is very unlikely. Until I get the rebuilt unit off the Jav I will not have investigated everything I can do.

As you say, brakes are very important.

[PJGD]

Keith, so the arrangement on your all-hydraulic Javelin is not like that as shown in Figure 47 of the hydro-mech system on Page 56 of the June 1950 Maintenance Manual. That shows that there are four slip-links in the system; one at the pedal, two at the rear brake rod, and one on the stop link. I assume that you are talking about the slip-link at the pedal/pull-rod connection. In the hydro-mech system that slip-link must surely be to allow the pedal to remain "up" even when the hand brake has been applied. I think that it serves no useful purpose for the all-hydraulic system and a conventional non-slip-link fork would be better.

I recall the story that Ben Shaw recounted of the time, probably in the 1960's, when he was driving to work along Western Avenue to his BBC OB office in Park Royal when he approached a roundabout at high speed and the brakes initially worked but then went straight to the floor! He ended up with the car in the flower bed in the middle of the roundabout. It was a such a shock to his system that all he could do was to sit there and smoke a cigarette until his nerves had calmed down. While doing that, a policeman came along and said to him "Hey, you can't park here you know!"

A post-mortem on the brake system showed that a steel backing shim behind one of the two seals had cracked in half so that the seal was no longer supported. Your experience, and that of Ben Shaw suggests that a split front/rear or diagonal brake system would be a worthwhile improvement to our cars.

Philip