Hey All

Im doing some shakedown runs in the old girl. yeah, finally on the road.
I had a brake question.
Note: its a 46 2 ton with power assist brakes.

question: when I drive it, after a few miles, the brake pedal get really hard, and in fact start to drag. What would cause this? a vacuum leak?
something with the check valve on the firewall?

Im confused, so advice welcome.

best regards

jay