installed new rear brake hose, bleed the brakes. brake pedal moves freely 1/2 inch and the spring pulls it all the way back. disconnected the vacuum line. took it out and did start stop driving, all was good for 5 minutes, and the brakes started to bind. also checked the handbrake, and their is plenty of free play in the cable under the car. the brake pedal seems to be rock hard when its binding, that makes me think its the master cylinder. Roger
Roger, when the pedal becomes rock hard, is there any free play first? In other words does the pedal still move the 1/2 inch, and then it becomes very hard, or does the fee play disappear and the pedal is immediately hard?
Tom
Hello Roger
I will bet that your problem is with the reaction valve, on the front end of your master cylinder.
This happened to me last summer with my 69 Series 2. Remove the reaction valve, clean the piston and lubricate with some light brake grease.
cheers
Doug
Tom their is still 1/2 free play. but rock hard after that.
Doug would the reaction valve function without the vacuum hooked up. and its only the rear brakes
Roger, it seems to me a strange one. My best shot, based on what you have said:
- If it were the reaction valve, it should be all four brakes locked. Also assuming you properly disconnected the vacuum, it should not be the reaction valve.
- If it were the master cylinder with vacuum disconnected, it should be all four brakes, as the master cylinder does not differentiate between front and back.
- Only the servo can separate the front from the back. I think the servo piston is sticking not releasing the rear, but I do not know if yours is hose as an early or late, which reverses the front and rear brake lines. But I would guess one of the two servo pistons is sticking. You may try, when the brakes are locked, loosening each front and rear line individually at the servo to see if that relieves the pressure and releases the rear brakes to help confirm.
Are you sure it is only the rears that are locking? Could the fronts also, but you do not notice them as much?
Tom
In addition, I guess possibly it could also be a crushed or clogged steel line holding pressure, or a stuck rear caliper piston. Loosening the line at the servo would help to determine this also.
Tom
took the vacuum line off the vacuum reserve tank. the line that goes to the manifold and plugged it.
without the vacuum the brakes were really week, with vacuum they seem normal.
checked the routing of all brake lines and vacuum hoses and all was correct.
the front line serves the rear brakes on my servo.
the fluid level in the bottles remains correct,
car has been driven only a couple of miles since restoration not above 35
front brakes may not be working but they did bleed just fine, will check they are working
front rotors were 84 degrees and the rear rotors were 250 degrees, with binding
I will make sure the front brakes are functioning
loosening the front line on the servo should relieve the binding rear brakes
surprised how weak the brakes were without the vacuum possible only the rears are working
Roger
front brakes are working. would think that points to the slave on the servo. going to try loosening the brake line on the slave that goes to the rear brakes, after the rain storm. Roger
Roger,
In your original post you mentioned that all the brake system was “new”. Is that “new” as in new assemblies (as in assembled master and slave/servo cylinders), or new as in newly rebuilt assemblies? I ask, as in the past there have been rebuild kits for the slave/servo with incorrect instructions about the orientation of the cup seals on the floating piston. I vaguely recall that one symptom of getting this wrong is that the brakes lock at one end of the car (front or rear) depending on how the system is piped. Rather than depend on my vague memory, it might be worth searching the archives for this issue…
-David
David
that is possible, I rebuilt the slave with a kit. maybe 6 years ago. just finishing the restoration now, seems like it has to be in the servo slave since its only the back brakes. I do remember something at the time of the slave rebuild about the cup seals. I hope the new kits instructions are correct, Roger
From what I recall, the incorrect instructions persisted for quite some time on at least one of the kits. I read that the Jaguar Service Manual is correct, though the language needs to be studied carefully. If in doubt, consult the archives. Good luck!
-David
That is what caused my problem.
Mike Moore
I rebuilt my MC a few years ago an experienced similar issues, but with all brakes dragging.
In my case it was the small metal piece that kind of sits “between” the piston and reaction valve that was sticking, causing vacuum to be applied to the booster. I found the one side had sharp edges from the manufacturing process and once they were filed off, it no longer got stuck and the problem was gone.
This will most likely not be the culprit here, unless the brake lines have been incorrectly hooked up.
I found temperature to be the trigger and isolated the issue to be in the MC by using a cold spray whenever the brakes would stick.
Cheers … Ole
Hello Roger
I did not play with the vacuum lines, so I cannot answer your question. My symptom was that the brakes would stay on and drag for 5 to 10 seconds before releasing, maybe more.
It’s a 15 minute job to clean and lube the piston in the reaction valve, so why not give it a shot. put some shop rags under, as you will lose a little fluid. I was thrilled when it worked for me, as I was facing a 2000 mile trip home at that point.
good luck
Doug
this is a case where only the back brakes lock up, and don’t release for an hour or so. going to pull out the servo and rebuild the unit again. according to the Jaguar service manual. comparing that to the instructions with the kit,
brakes are now working properly. installed a new servo and vacuum chamber, runs out perfect, I can drive my car now yes yes yes
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