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MG MGB Technical - Loss of pressure to brake pedal

right i have a rubber bumper, 1977 mgb gt.

over the course of a couple of days, there was a gradual reduction in the pressure on the brake pedal, with it responding slower each time. then, on one journey, there was no pressure at all, and the brakes just didnt work. scary.

there is enough brake fluid, so any ideas what it could be. could be the master brake cylinder, what would i need to do to test it?

thanks
Daniel Turner

Daniel. Yes, if the fluid in the reservoir is not going down, the master cylinder is the place to check. You can pull a front wheel (put the car on jack stands) and have someone depress the brake pedal while you watch for movement of the brake pads. However, there is very little movement there. Trying to turn the hub should tell you if it is locking up. I normally remove a rear wheel, pull the brake drum and watch for movement of the brake shoes. But, without the drum in place, you need to do this carefully so as not to push the pistons out of the wheel cylinder. Les
Les Bengtson

The master is bad. It's leaking internally.
Mike MaGee

Daniel To test your master cyl put your hand on the brake as gentley as you can and see if the pedal goes down.You must be as gentle as you can (just enough to strech the spring) if you stand on the pedal hard you "set" the primary cup against the cyl and the pressure will hold. all the best Denis
DENIS

"gradual reduction in the pressure on the brake pedal"

I'm tempted to say 'get a stronger leg'.

I'm not sure what your symptom is, whether it is the pedal gradually sinking to the floor or whether you are having to press harder and harder to get the same retardation. If the former then definitely the master seals are at fault. If the latter then it could be a number of things including gunge in the hydraulics blocking things up.
Paul Hunt

This thread was discussed between 25/10/2004 and 27/10/2004

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