4 wheel drums? How did you bleed the master- with plugs or with the tubes to recycle the fluid, on a bench or in the truck? I would look first at the master- if it's not defective or damaged, then it might need to be re-bled at a different angle to get all the air out. As Jim said, you can get air in the system. Occasionally, raising one end or the either of the truck can help to solve that problem...but not always

Do you have a proportioning valve setup? Did you install the dummy plug in the valve to bleed it properly? Need more info on your system to help...

discs or drums
maser cylinder bore size
proportioning valve or not
residual pressure valve(s) ( RPV ) installed or not

Last edited by Norcal Dave; 07/30/2017 4:44 AM.

~ Dave
1950 Chevrolet 3600 3/4-ton with 261 engine & T5 Transmission