StephensBPE

Hi all,

Are the master cylinders on these cars supposed to leak out the back? Or, more accurately, is the rubber dust boot thing on the back of the master supposed to function as a seal? I'm working on a '66 Cutlass with power drums on all four wheels. It needed wheel cylinders, shoes, a booster, and a master. I couldn't get the system to bleed, and after much frustration noticed that the master cylinder was leaking out the back, into the booster. Just received the new AC Delco master, and now I have the same problem. I know the master is at fault because this new one leaked into the rubber boot on the back while I was bench bleeding it. I installed it anyway because the rubber boot seemed to be sealing the cylinder; I thought maybe it's supposed to seal around the push rod. It did, until I pushed on the brake pedal, where despite very careful installation, that rubber boot got torn to pieces. So it seems like I either got two bad master cylinders in a row, got the wrong master for this application, or am missing some trick to installing the master. Any help is appreciated, this is starting to drive me crazy.

Fun71

Leaking out the rear of the piston seal is not normal.

72455442RA

x2

StephensBPE

Thanks. I didn't think so, but this is my first encounter with power drums, and I figured I should check.

joe_padavano

The rubber seal is to seal the vacuum chamber of the booster, not to seal the M/C. The piston seal inside the M/C is what prevents fluid from coming out the back. Yours is bad.