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I am trying to rebuild a brake master cylinder on a 77mgb. I have removed the primary and secondary pistons from the main body but and having some difficulty removing the pressure differential piston assembly. I have removed the pressure failure switch. The manual says I should apply air pressure to the primary outlet port. Unfortunately, the piston does not come out. Am I missing something? Any suggestions would be appreciated.


I had exactly the same problem on my 77 rebuild. With the switch removed, I was able to reach in the hole with a screwdriver or something and coax the piston to move a bit. Then moving it back and fourth a few times I was able to get it out.

After I had it apart, it looked like I could have gotten it moving easier by pushing it a bit deeper into the bore to free it up. If you do that don't push it so far that you hide the ring on the piston that you need to pry on through the switch hole.

Also, I think I saw something, presumably on this BBS, about a set of instructions that were written for rebuilding that master cylinder. Take a look on both the general and tech threads and see if it is still there. I think it was just a few days ago that I saw it.

C R Huff


Here, I found it. It is just a few posts earlier than yours.


Posted 23 February 2009 at 18:03:02 UK time
S.L. LaPaugh, Virginia, USA
Our March newsletter is out. I wrote an article on rebuilding the '77 brake master cylinder I thought I'd post the link for those interested. Article is on page 7. Enjoy. Steve

C R Huff

This thread was discussed on 27/02/2009

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