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MG MGB Technical - Brake bleeding

Lengthy story: My 1976 Roadster has been off the road for about 3 years. I decided to move it to do some work on it but couldn't get any gears. Immediate action: bleed the clutch. Did that three or four times, still no gears and about half a pedal. Decided that, because it had been sitting for so long, maybe I should replace the fluid. Did so, still no gears. Now decided that I should take a look at the master cylinder. And, while I was about it, maybe I should look at the braking system.
Took off both masters and rebuilt them using a standard rebuild kit. When I checked the front brakes it became apparent that the calipers were siezed. Put them on the bench but they were obviously past anything that I could do, so I replaced both calipers and discs.
Now decided to take a look at the rears. When I took the drum off they all but fell apart! So, new shoes, new springs and new wheel cylinders. Because I had managed to screw up one of the brake pipes I changed out both back pipes plus the flex pipe.
I have now bled the brakes four or five times. I've been round and tightened up all the connections, but all I get is a good pedal initially and then it falls away. After a couple of minutes the pedal goes to the floor.
Can anyone suggest an answer? All I can think of now is to buy a new master cylinder and put it in.
I haven't got anywhere with the clutch because I am waiting for a new slave cylinder.
Mike

If there are no visible leaks from anywhere then the MC is no good - fluid bleeding back past the seals to the reservoir. It seems not uncommon to have rebuilt MCs still to be faulty, or even to be *made* faulty when they were OK before by rebuilding them, especially the later dual circuit ones.

If you have a hard and high brake pedal to begin with, and the pedal only sinks gradually with continued pressure, then the rest of the system would seem to be air free, at least. Unfortunately you are going to have to go through all the bleeding again when you have fitted the new master.

Not sure what you mean by 'half a pedal' for the clutch. Hydraulic problems or not the pedal should always go to the floor. If it doesn't there is either a mechanical problem with the pedal or master restricting travel, or the master and hydraulics are OK but there is a mechanical problem at the slave, clutch arm, release bearing, cover-plate etc. which again is restricting travel. If reverse grinds when attempting to select it then you have clutch drag i.e. insufficient movement of the pressure-plate, usually due to air in the system or severe wear of the pedal and push-rod linkage or an incorrect push-rod. If you just can't get it into gear but there is no grinding in reverse then it is probably a mechanical problem with the gearbox.
Paul Hunt

You can't gt any gears - do you mean you can't get it to go into gear because it makes grinding noises, or do you mean that you can put it in gear but then nothing moves?

If it grinds, the clutch has probably frozen / rusted to the flywheel. Search the MGA archive for lots of tricks to free this, or go to mgaguru.com

If you can put it in gear but the car doesn't move, the clutch is again likely to be the candidate, this time the friction plate is toast or the clutch cover has too little pressure left to be effective. That's an engine-out job.


dominic clancy

This thread was discussed between 05/10/2008 and 06/10/2008

MG MGB Technical index

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