I just replaced a wheel cylider and and bled the brakes. when I took the car for a test drive the pedal is still squishy and when stopped at a light it will slip and move doen without any added pressure. If I wouldn't allow it to move sown the car would roll. I bled the brakes again but not much air came out, just a few bubbles. I went for a test drive but I still have the same proble. Is the problem in the master chylinder. I think that maybe a seal is bad and when the pressure builds up in the cylider it allows the fluid to flow past the seal and I lose brake pressure. Thanks in advance.
It does sound like a master cylinder problem...however...have you replaced the calipers? They can cause the same issues.
I checked the calipers and seals well when I did the initial maintanance on the car. I even reomved the pistons so that I could replace the dust boots on them and check for brake fluid ozzing past the seals and they looked good. I also haven't notice any fluid leaks, certainly not enough to justify that kind of loss in pressure. The front brakes were also R&Red recently before I bought the car because there was very little wear on the pads and rotors.