I have a 69 with manual disc brakes and for some reason I am unable to get the system to hold brake pressure. I have replaced the 4 calipers and master cylinder and bench bled the master cylinder and gravity bled the brakes. I started off with the pedal being hard and high but over a short period of time (30 minutes driving or so) the brakes are almost to the floor. This is the exact problem I had before replacing the brake components. When I checked the fluid in the master cylinder its right at the top, zero leakage. Any suggestions?.

 

It sounds like you have a bad master cylinder since your not losing fluid. I have had brand new ones do the same thing.

 

ghia, welcome to the forum.i agree.