40 Buick master cylinder problem

[michel88]

The master cylinder is leaking very badly in my 40 Roadmaster. It is leaking out where the brake pedal linkage goes in the back of the cylinder. If I fill it up it will leak out completely over night. I got a rebuild kit ordered from Bob's and I hope this will correct the problem. Is there a seal where the linkage goes into the cylinder? Thanks for any tips that you can give me.

[Barney Eaton]

I had a similar problem and the metal retaining clip had come out or the groove allowing the piston to travel too far back and leak. I probably could have solved the problem by just replacing the clip, but it was time to clean it, hone the bore and put in a new kit.

my local auto parts store had one listed for a later model ('48 if I remember correctly) and it looked like my parts and it worked perfectly.

[michel88]

Thanks Barney, this may be my problem. the master cylinder was fine with no leak and all of a sudden it developed the problem and leaked out completely in a matter of hours. I will take it apart when I get the kit.

[michel88]

This weekend I pulled the master cylinder and put in a rebuild kit from Bob's. I honed it lightly and cleaned it up using brake fluid. I didn't see any obvious reason why it was leaking so badly, and the snap ring was still seated properly. I guess it was leaking past the piston seal. Anyway it is back in place and does not leak.