I have good brakes (engine off) as soon as I start the truck the brake pedal goes about half way down and are spongy. I took the truck in for yearly tuneup and shop told me master brake cylinder was bad. I did the pre bleed of it and replaced it. I had the shop do the bleed of the entire system. They said they bled all four wheels four times and found no air in the system. I had the system power bled to replace all fluids incase of water in the system. I changed my brake pads with high quality pads. While I was changing the brakes I checked all of the wheel calipers and they are in great shape(no leaks). Problem still exists.... well now I am at a loss.... Brake assist?

 

Sounds like either the booster or the proportioning valve to me.

 

i dont know if it matters with a pressure bleeder but there is a bleeder on the ABS valve. could also be the front brake (rubber caliper) hoses swelling. a bad booster usually slowly drops to the floor or some weird stuff like that. sounds like there is still air or a rubber hose is swelling.

 

My vote is the booster. There is no proportioning valve on '87-up; just a residual pressure valve on the MC, and it can't cause this symptom.

 

The problem was in the back end. The cable that runs to the back for the adjuster was streched.... almost to the point of braking. Since this was streched the brake shoes to the back did not put any pressure to the pedal. the pedal travel is a combination of front and back..... thanks for all of your replies