My buddy has a 92 f250 idi supercab with 6 inch lift blocks and 37 inch tires. Its ridiculous. Anyway, his brakes have always sucked. We did a master cylinder, rear wheel cylinders and shoes, replaced a few brake lines, and new hoses. They STILL are scary. The pedal sinks to the floor but if i pump the pedal it will come back up for a few minutes until it loses pressure again. However, when the pedal is high the brakes are even worse. When its high up the pedal gets hard and braking is severely limited. If i let it stay on the floor it actually stops alot better (even though its still dangerous). No fluid loss and i dont see any leaks. Im at a loss. Is it time for a booster?

 

Bumpity bump

 

Almost sounds like a defective master cylinder. What were the brakes like before you changed it the first time?

 

Without the truck running are they hard or still pretty soft and spongy

 

first thing to do is check vacuum. you want to have at least 19 inches. and it should recover almost immediately after stepping on the brakes.

to test the booster, step on the brakes after the engine has been off for a while, is it hard or soft? soft pedal means it is holding vacuum. hard pedal means you have a leak.