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MG MGB Technical - Brake servo gone?

I've been checking the archive and I think that I may have lost the brake servo.
I've got a pedal that's as solid as a rock with no perceptible "bite" point and a strong leg is required to stop the car. Also, I'm losing brake fluid slowly. This all points to servo failure.
But: I have no white smoke from the tailpipe and pressing the pedal has no discernable effect on engine idle which would seem to eliminate a servo leak from things according to previous threads on this subject.
The vacuum connection to the servo is good having had a nice, new hose a few months ago.
Am I definately on to strip the servo here or is there something else that could be causing these servo-failure-like symptoms. The reason I ask is that it's a '77 car with the integrated servo, so I'd like to be damned sure that I'm heading the right way before subjecting myself to all that grief.
T J C Cuthill

Question Tim, is there any play that can be setup on your pedal to servo/brake cylinder rod? the rod should be loose so that the master cylinder plunger can allow the fluid to return to the chamber and release the braking pressure.
Tatty

Hmm, it's a thought, but why would that produce the "no servo" effect? Also, it was all working fine last week. However, ever one for eliminating all possibilities before taking on a big job, I shall subject this assembly to a wiggle test before driving home tonight.
T J C Cuthill

Has the vacuum hose collapsed?
Paul Hunt

I already checked the vacuum hose and it's OK. I think that there are two faults here as the fluid loss is getting worse. I reckon that the Master Cylinder is on the way out (can't see any leaks anywhere else and it seems to be leaking equally from the front and rear circuits) and the slight fluid leak into the servo has put paid to that as well. I'm guessing that the missing fluid is sitting inside the servo shell, I haven't lost enough yet to get it to the level where it would run out over my foot.
Come to think of it, while I was looking at it earlier, I noticed that the vacuum supply attaches quite low down on the servo. I wonder if enough fluid has found its way in there to have gunged up the non-return valve?
T J C Cuthill

I'm having the exact same problem. Although i have detected no leakage from anywhere on the car ('80 MGB), it takes a strong (and long) leg to get the car to stop.

Would it be really stupid if it were just the spring on the pedal being incredibly strong?
Chris

The symptoms you describe are exactly the same as when I had a servo failure on my S10 pickup. Breaks were hard, no engine symptoms...no smoke. Just a small crack in the diaphram caused the whole thing. I think it's time to stop chasing ghosts and just change the thing out before you become an integral part of some other object. Rob
R. L Carleen

OK, that's what I was expecting (the servo failure, not the potential impact, that is). I've got a kit for the servo, as new ones seem to be either unavailable or priced as "we've-got-one-and-know-they're-unavailable". Since I've got to remove the Master cylinder to do this job, I'm going to change that at the same time, it seems daft not to given the effort involved. I'd kick myself if that still gave trouble after all the hassle.
T J C Cuthill

It might be the one way valve in the vacum connection at the servo that is not working. This happend to me and gave me the result you have. No servo power and it started losing brake fluid. You can take the valve out of the servo by pulling it out. Itīs a press fit. After you got it out try to suck air in the normal direction through the valve. Remember itīs a one way valve so air only goes - out - of the servo.
God luck
Manfried
Manfried

This thread was discussed between 05/03/2003 and 06/03/2003

MG MGB Technical index

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