looking for residual valves

[dbc105]

Does anyone have a bad master cylinder lying around? All the master cylinders I have found for my '68 do not have residual valves behind the seats and I am having a hard time with my brakes. I don't want to cut my lines to install inline valves because I plan to do disc brakes a little later and there is not enough room between the cylinder and the fender well to attach them directly to the cylinder. When I bought the car the brakes worked but not good and I have been working on other things along the way but now I need to be able to drive the car and the brakes are just not up to it. I can mash the pedal to the floor, all 4 wheels are adjusted up and new wheel cylinders and new master cylinder and bleed on all 4 corners with a pressurized bleeder system. It will have full pedal for about three times and then it just starts going to the floor. I did a bunch of talking to brake people around here and it seems that without the residual valves to maintain a little pressure on the lines that is what happens. So now I am looking for the valves from an old master cylinder so I can install them in the one I have. I forgot to mention the car has drums on all 4 corners. Any and all help is appreciated.

Thanks,
David

 

[Big John]

That sounds more like a bad master cylinder to me.

 

[dbc105]

it's the second one I've put on. They both did the same thing right out of the box. I found a site called BrakeMan.com and in his tech section it tells about the residual valves and if they are not there and that is exactly what mine is doing. When I took the first master cylinder back I removed the seat where the brake lines go and checked and there was nothing there. I have read in other places that the reman folks don't install them. I don't know but I'm guessing the one I have on the car now doesn't have them either. It looks like in the picture of the master cylinder rebuild kit that they may be in that so I may end up getting a rebuild kit to get them.

 

[moparchris]

Does anyone have a bad master cylinder lying around? All the master cylinders I have found for my '68 do not have residual valves behind the seats and I am having a hard time with my brakes. I don't want to cut my lines to install inline valves because I plan to do disc brakes a little later and there is not enough room between the cylinder and the fender well to attach them directly to the cylinder. When I bought the car the brakes worked but not good and I have been working on other things along the way but now I need to be able to drive the car and the brakes are just not up to it. I can mash the pedal to the floor, all 4 wheels are adjusted up and new wheel cylinders and new master cylinder and bleed on all 4 corners with a pressurized bleeder system. It will have full pedal for about three times and then it just starts going to the floor. I did a bunch of talking to brake people around here and it seems that without the residual valves to maintain a little pressure on the lines that is what happens. So now I am looking for the valves from an old master cylinder so I can install them in the one I have. I forgot to mention the car has drums on all 4 corners. Any and all help is appreciated.

Thanks,
David

David,

Drum brakes require a very low pressure to keep the pads out against the drum. A "residual pressure valve" has a spring and ball/seat that shuts at a pre determined pressure (usually 1 psi). When the valves aren't present the shoes are allowed to be pulled back creating air space between the shoe and the drum. With this knowledge, one can see what the result would be. The first pump will go to the floor with each subsequent pump the pedal will get harder till the driver releases the pedal and drives for a few seconds or more without hitting the pedal then the cycle will start again. I really think you have another problem. The symptoms you describe are not consistent with the lack of residual pressure valves. Just so you know I have quite a bit of experience with drum brakes and have installed residual valves inline from wilwood before.