hard brake pedal

i am having a problem with my pick up. it is an 89 k1500 4wd. ever since i purchased the truck back in 97 i have always had a hard brake problem in the truck. the truck is also hard to stop and forget it if i need to make a panic stop. when i first purchase the truck i changed the booster, master, porportion valve, rear wheel cylinders, drums shoes. in the front i changed the pads but i didnt bother changing the calipers since the truck doesnt pull when i apply the brakes. all the hoses were also changed. after changing everything the pedal was still the same. does anyone have an idea on this. i heard that i might have a mixed up booster/master combo meaning that the booster is for one application and the master is for another for example lets say the booster is for the truck with the heavy duty brakes where the master isnt. does this make sence to anyone. any input would be greatly appreaciated. thanks

anyone???

Did you check the vacuum at the power booster? There is a one-way valve incase the booster leaks, perhaps it is installed incorrectly. Or the vacuum port is clogged in the intake manifold.

Engine off, apply pressure on the brake pedal. Start the engine, does the brake pedal drop a little?

//2000CAYukon

yes i checked the vaccum at the booster. there is 21" of vaccum. i removed the check valve and it held air so the check is good. if i hold the pedal while off the pedal goes down very little.

For diagnostic purposes can you remove the check valve from the line and test the brakes to see if there is a change? Perhaps the valve holds air in both directions...

there is a little change in the pedal but not much. i ordered a new booster today since i have the 10 1/2" booster on the truck now and it looks like it is supose to have the 9" booster instead. i have also heard that the porportion valve might be bad but i cant seem to find one from the parts store.