You probably don't have enough freeplay between the brake pushrod and the master cylinder piston. What is happening is that the master cyl piston isn't coming all the way back to the fluid pressure release port. The pushrod that protrudes from the power brake booster is adjustable. If needed, screw it in some to shorten it. Check first that the brake pedal is returning back ALL the way.

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.