First of all, nowhere will it let me ID the actual vehicle I am working on so Actual truck is a 69 IH LOADSTAR 1600 WITH 345 ENGINE. Concern: Brakes overheat and stay applied after driven only a few miles. Tech drove truck 4 miles and then immediately lifted all wheels to confirm cannot spin any of the tires. Crack the rear bleeder screw, there was pressure in the system, all tires then spun free. With truck not running, pump brakes and all tires again would not spin. Crack front bleeder screw and all tires released/spun free. Pump brakes again w/o truck running, bled the hydrovac and again all wheels released. Perform the same procedures with truck running - start, pump brake pedal one time and wheels are still free, pump brake pedal multiple times and wheels lock until bled in any location. How do I diagnose if it's the single firewall mounted master cylinder or the frame mounted hydrovac assy?

Bill Schwoeppe
Owner/Technician
Affordable Auto Repair & Tire
Marthasville, Missouri, USA