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ONCE AGAIN, THANKS JOHN. BEEN WORKING SO WILL TRY THE CHECK YOU SUGGESTED & WILL POST REPLY THIS WEEK END.
2 posters
loss of brake pressure
davidjones66- Posts : 11
Join date : 2011-03-09
jaybee- Posts : 11
Join date : 2010-10-03
Hi Dave
I can't comment on parts availability for these cars, because I'm not a Jaguar expert. However, I've been working on cars for a living for over thirty years now, so you could say I know a thing or two.
There is a procedure for checking operation of a vacuum brake servo, as follows:
Start the engine, run for a minute or so, apply the brake pedal and switch off the engine. Pump the brake pedal to exhaust the vacuum from the servo. The pedal should go hard and rise after a few applications.
When this happens, keep the pedal applied and re-start the engine. The pedal should fall slightly as the servo vacuum is replenished. If this is the case, your servo is OK.
Whilst replacing (or even re-building) a brake master cylinder is relatively easy, rebuilding a servo is not. The two halves of the servo are difficult to separate, and usually require a special tool (purchased or home-made) to do so. A reconditioned unit is the most practical and cost-effective solution.
Regards
John
I can't comment on parts availability for these cars, because I'm not a Jaguar expert. However, I've been working on cars for a living for over thirty years now, so you could say I know a thing or two.
There is a procedure for checking operation of a vacuum brake servo, as follows:
Start the engine, run for a minute or so, apply the brake pedal and switch off the engine. Pump the brake pedal to exhaust the vacuum from the servo. The pedal should go hard and rise after a few applications.
When this happens, keep the pedal applied and re-start the engine. The pedal should fall slightly as the servo vacuum is replenished. If this is the case, your servo is OK.
Whilst replacing (or even re-building) a brake master cylinder is relatively easy, rebuilding a servo is not. The two halves of the servo are difficult to separate, and usually require a special tool (purchased or home-made) to do so. A reconditioned unit is the most practical and cost-effective solution.
Regards
John
davidjones66- Posts : 11
Join date : 2011-03-09
John, sorry about delay in replying been away. One of my thoughts after checking all calipers was the servo & your explanation was exactly the symptoms as it happened. Is there any way of confirming/eliminating the servo while on the car? I use a local independant Jag/Daimler guy who's allways willing to chat but he's holidays till the end of next week. Are the seals available? I presume if servo is off it makes sense to renew all the seals & any other brake related bit that looks worse for wear? Nice to talk to people with the same car & problems. Regards & thanks, Dave.
jaybee- Posts : 11
Join date : 2010-10-03
Hi David,
I haven't been on for some time, and I see no-one has posted any replies to your problem. I'm almost 100% certain that your problem is the brake master cylinder. Modern ones are in fact 'tandem' or 2 cylinders arranged end-to-end. This means there are actually 2 separate brake hydraulic circuits for safety. It sounds like one of the cylinders is failing due to faulty hydraulic seals. Classic symptoms are a 'long' pedal, reduced braking effort, no visible leaks or loss of brake fluid, illumination of the brake system failure warning lamp when the problem occurs (whilst the brake pedal is depressed).
The solution is to either replace or rebuild the master cylinder with new seals, and bleed the brakes.
Good luck!
John
I haven't been on for some time, and I see no-one has posted any replies to your problem. I'm almost 100% certain that your problem is the brake master cylinder. Modern ones are in fact 'tandem' or 2 cylinders arranged end-to-end. This means there are actually 2 separate brake hydraulic circuits for safety. It sounds like one of the cylinders is failing due to faulty hydraulic seals. Classic symptoms are a 'long' pedal, reduced braking effort, no visible leaks or loss of brake fluid, illumination of the brake system failure warning lamp when the problem occurs (whilst the brake pedal is depressed).
The solution is to either replace or rebuild the master cylinder with new seals, and bleed the brakes.
Good luck!
John
davidjones66- Posts : 11
Join date : 2011-03-09
Hi guys, just been to Forres/Lossiemouth in Scotland on a weeks tour. 1339 miles round trip with hardly a problem, however....on 2 different occassions about a week apart I applied my brakes & the pedal went half way to the floor! The brakes still worked & the problem only lasted 5/10 mins but most perterbing to say the least. First time we stopped in a layby & I checked all round & found nothing obvious, no leaks, no fluid loss then no futher trouble till about a week later.The second time I took it to a local garage where they put it up on ramps & went all over but found nothing wrong & of course because the pressure was back no real way of checking anything exept visual inspection of pipes, pads, discs etc. Again nothing wrong!All the way home from Scotland no trouble at all. My cat is a 1985 3.6 manual Cabriolet.Has anyone else had this problem or any ideas at all? Regards, Dave from Merseyside.
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