Brake Problems

[OSUCowboy27]

1998 T-100, 4wd, 3.4L, no abs

The brakes will "pump up" but not stop good. I changed the pads and shoes, checked for leaks and changed master cylinder (expensive). Still soft and still have to pump them up. I bled the brakes until the fluid ran clear and even got a little air out. I bench bled the master cylinder before installation. Could I still have air in the system? What else could it be? Also, there was a proportioning valve attached to the rear diff, I bled that and got a little air. Are there any adjustment on the proportioning valve and what is its purpose? Any help would be greatly appreciated.

[The_Mechanic_33]

Check the caliper slides and make sure they are not frozen,same goes for wheel cylinders make sure the pistons are not frozen in the bore.also check the slides on the front spindle where the pads ride they sometimes form pits or groves and the pads get stuck and can no longer travel as they should.(if thats the case ten weld and grind to rectify).Also make sure your rear adjustment is up to snuff not to tight though.