'67 master cylinder rebuild-check valves?

[Steven B.]

I have reason to believe my master cylinder is original to the car. I had a leaking piston seal in the right rear caliper and the ensuing repair resulted in a decision to rebuild all calipers, replace the rotors and replacement of all brake lines, hoses as well as the parking brake system (I'm probably fortunate that I don't have the body off by now as a result). I decided to rebuild the master cylinder while I was at it, and ordered and received a Raybestos kit. Among other parts, it included two brass tube seats, and two springs and residual pressure check valves. However, I didn't pull any springs or valves out when I removed the original seats. I have done a little research and determined that the check valves, I believe, are specific to drum brake systems, and the kit covers multiple years. I understand the need to maintain a small amount of pressure at wheel cylinders in drum systems. Here is my question. I looked at the valves when placed against the back side of the seats, and can't understand how brake fluid pressure would get past the valves if they are against the brass seat on the inside. The springs would appear to hold them against the back of the seat. Unless a master cylinder for a drum brake system is machined differently behind the seats to accommodate some space to relax the springs under normal conditions, I am a bit confused as to how the primary and secondary piston push fluid past the checks and in the lines to the distribution block.
Bottom line: since my car is disc brake, I left the checks out when I replaced the seats. Do the checks even belong in a disc brake system? If necessary I can change the seats out. Fortunately, brake parts don't tend to be that expensive.

Steve

[Joe L.]

Re: '67 master cylinder rebuild-check valves?

I have reason to believe my master cylinder is original to the car. I had a leaking piston seal in the right rear caliper and the ensuing repair resulted in a decision to rebuild all calipers, replace the rotors and replacement of all brake lines, hoses as well as the parking brake system (I'm probably fortunate that I don't have the body off by now as a result). I decided to rebuild the master cylinder while I was at it, and ordered and received a Raybestos kit. Among other parts, it included two brass tube seats, and two springs and residual pressure check valves. However, I didn't pull any springs or valves out when I removed the original seats. I have done a little research and determined that the check valves, I believe, are specific to drum brake systems, and the kit covers multiple years. I understand the need to maintain a small amount of pressure at wheel cylinders in drum systems. Here is my question. I looked at the valves when placed against the back side of the seats, and can't understand how brake fluid pressure would get past the valves if they are against the brass seat on the inside. The springs would appear to hold them against the back of the seat. Unless a master cylinder for a drum brake system is machined differently behind the seats to accommodate some space to relax the springs under normal conditions, I am a bit confused as to how the primary and secondary piston push fluid past the checks and in the lines to the distribution block.
Bottom line: since my car is disc brake, I left the checks out when I replaced the seats. Do the checks even belong in a disc brake system? If necessary I can change the seats out. Fortunately, brake parts don't tend to be that expensive.

Steve

Steve------



4 wheel disc brake systems do not use any check valves in the master cylinder. Disc/drum systems use check valves only in the DRUM brake circuit.

[Steven B.]

Re: '67 master cylinder rebuild-check valves?

Checks in the disc or drum circuit? I'm still confused about how the checks would allow pressure past the seats. It would make more sense if the springs and checks were turned around and the springs were against the back side of the brass seats. It doesn't seem as though the checks against the back of the brass seats would allow any pressure to the brake lines leading to the distribution block.

Steve

[Joe L.]

Re: '67 master cylinder rebuild-check valves?

Checks in the disc or drum circuit? I'm still confused about how the checks would allow pressure past the seats. It would make more sense if the springs and checks were turned around and the springs were against the back side of the brass seats. It doesn't seem as though the checks against the back of the brass seats would allow any pressure to the brake lines leading to the distribution block.

Steve

Steve-----

I mis-typed in my above response. I've corrected it.