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MG MGA - Brake Issue

I have a '60 coupe (disc brakes in front, drums in rear). Car sat several months without being driven. I rebuilt master cylinder and bled the brakes. Symptom is that pedal is fine for a few applications, however, becomes quite spongy quickly. If I pull the pedal up with my foot as far as possible a few times the brakes become firm again.

What can I do to maintain firmness?

Michael Dawidoff

MD, this sounds like the problem of newly installed sticking seals. There's much comment on this in the archives. Its worth persevering with the piston movement even if its not returning immediately after release of pressure since it may improve with use. If not one suggestion is that one manually works the piston up and down the cylinder with a bolt that can be threaded into the back of the piston sufficient to gain a purchase. This does of course entail a re bleed.
J H Cole

Have you got a return spring on the brake pedal?
Bob Turbo Midget England

Thanks for the suggestion. I'll have a look through the archives.

Note that I did in fact install a new return spring.
Michael Dawidoff

Sorry but if you have a return spring fitted then how can you pull the pedal up with your foot? it should already be up by the action of the spring?
Bob Turbo Midget England

Hi Bob,

The spring will only pull the pedal back maybe 1/4 of the return and then stop. The typical sequence is:

Brakes fine for a few applications.
Then become quickly spongy with pedal travel increasing to the floor. At this time pedal return is about 1/4. I can then pull the pedal back with my foot and sequence starts again with fine brakes.
Michael Dawidoff

Since the pedal return spring is there, It should COMPLETELY return the pedal to it proper place, even if the M/C piston is stuck. The pedal is not a hard connection to the piston. It has a pin which slips into the recess of the piston. It is free to return without the piston. You may have too much friction in the pedal pivot preventing the return of the pedal. Or you may have too tight a dust boot on the M/C. I'd recommend taking the pivot apart and check for the proper bushings and sleeves to be in place and not ground down too much. Fix this first before you start with the hydraulic side of the brakes.
Chuck Schaefer

Chuck - good point. Hadn't really thought about the fact that the pedal should return on its own as it isn't connected to anything in the MC. I'll have a look. Now that you mention it, I'm suspecting it could be the gasket in the front possibly causing some friction.
Michael Dawidoff

Thanks Chuck we are on the same wave length.

Michael you need to resolve this problem first and hopefully your problems will disappear.

However the pedal is causing a problem and must be rectified but there could be another lurking waiting to be identified.

May I ask why did you rebuild the master cylinder?
Robert (Bob) Midget Turbo

Hi Bob,

Rebuilt the master as the car had sat for about six months without having been driven. Brakes were kind of "stuck" so I figured I should rebuild and bleed to ensure proper braking before getting back on the road.
Michael Dawidoff

Took Chuck's advise and checked the pedal assembly. Lubricated around the pedal bushings and this remedied the problem of the sticky brake pedal!!! Thanks for getting me on the right track.

Michael Dawidoff

This thread was discussed between 15/02/2011 and 18/02/2011

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.