Classic/Antique Car Repair: 1949 chevy fleetline, Brakes lock up after replacing master cylinder.

Question
I have a 1949 chevy fleetline all original,the problem is the brakes,I have replaced all wheel cylinders,brakes,brake lines, and rebuilt the master cylinder,I still have the same problem as when I started and that is after just a few miles of brakeing around town the pedal is way up and the the front and rear brakes lock up and then I have to open a bleeder valve let a litte brake fluid out and then I can go again long enough to get home,everything is rebuilt, after doing all of this work the problem never went away ,I even blew all of the brake lines out while I had everything apart.Any suggestions would be much appreciated,thank you.


Answer
The push rod that operates the master cylinder is not adjusted right - the rod must be adjusted so that the brake pedal has to be pushed down 1/2 inch before the rod contacts the cup inside the master cylinder.  If you neglected to do this, pressure will build up in the master cylinder and apply the brakes even without touching the brake pedal, because the pressure relief valve inside the master cylinder is not being opened - it only opens when the cup is allowed to return all the way to the back of the master cylinder.

Dick