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MG MGA - master cylinder mystery

I’m into my sixth week of trying (intermittently, while I work on the rest of the car) to bleed my clutch, still with zero success. Following Barney’s advice (below,in the thread "cultch won't bleed"), I took the new master cylinder apart and found that there was a bit of sludge in it, probably from an old right front brake line that I unwisely reused. I’ve just replaced it with a new one. I cleaned and polished the master cylinder pistons and bores and reassembled it. The pistons slid smoothly back and forth when pressed and air spurted out of the back holes where the lines attach.

I put the master cyl back into the car and found that in order to get the push rod clevis pins through the pedals, I had to push each piston all the way back into its bore, so that no more movement was possible. This is with the push rods shortened as much as possible. The pedals are in their correct positions, too.

My first thought was that I had put the master cyl together wrong, so I removed and disassembled it again, paying close attention to the manual to be sure that everything was present, in place, and the right way around. I put it back into the car and there was no change: the pistons had to go all the way back to get the clevis pin in place.

The strange thing about this is that before I took the MC apart, the whole pedal-push rod assembly fitted together and moved smoothly. I’m using the same pedals, push rods, clevis pins, and master cylinder as before.

I must be doing something wrong, but I can’t see it. Can anybody say what the problem is? Many thanks in advance!!
Mike

M.E. Whalen

I find it sometimes difficult (but not impossible) to R&R the push rods without moving anything else. It is a close fit. It is not too difficult to loosen the bolts securing the master cylinder to the bracket, then remove the front bolt, then lift the front of the master cylinder slightly.
Barney Gaylord

Mike
Approximately how much push-rod thread was showing before you first took the M/C off the car?
Is it possible that there is something in the bore that is preventing the pistons from traveling to their proper positions?....Have you compared the new seals with the old ones, to make sure they are the right parts?
Moss has posted a "Warning" in its catalogue about replacement pistons and seals....Maybe your new parts are too thick....Just a thought.
Edward
Edward Wesson 60MGA

This thread was discussed between 08/02/2014 and 11/02/2014

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