brakes not braking

[joebuick]

Hey Guys,, I have a 80 K10 that I am restoring with my grandson and have come up on a puzzler. The brake pedal will get very hard at the bottom of its travel and does not stop the truck very well. A few close calls and we have parked the truck till we figure this out. I installed new rear wheel cylinders w/ new shoes. The front disc pads were both OK so didn't do anything there. We installed a new master cylinder and still no help. Since this truck had been parked for several years,,, could maybe the proportioning valve be plugged? I have seen flex brake lines collapse inside and lock up the brakes but these do not lock up but get VERY hard the last inch or so and danged if it don't seem like the truck speeds up,,!!! Any help on this??

[jake wells]

it been a while since i fooled with brakes.It sounds like you have either a bad proportioning valve or the lines are part way collapsed not allowing enough brake fluid to enter the caliper.

[Slofarmtruck]

I had similar issues with my truck and it ended up being the front rubber lines collapsed.

[motornut]

does it have a booster/leaking?

[asphaltburner]

Yo! Did you "bench bleed" the master? Are the Sx the same as before your work on the brake system?
Todd.

[silvereagle07]

It sounds to me like you need to replace the front pads and turn the rotors. The hard pedal at the end of travel usually happens when the pads are glazed,. The rotors may be rusted do to sitting up a few years. It's acting like glass on glass slipping until manual pressure takes over (no friction to slow it down). Also if you did not turn the rear drums when installing shoes. The shoes will take a while to seat into the drums. Be sure to bleed the system correctly to get all of the air out of the lines. Gravity bleed then manual bleed.

[joebuick]

Hey Guys,, Yes, the symtems are same as before is why I started fixing on it. There are no leaks and Yes, I did a "bench bleed" on the master before installing it. I had the rear drums turned when I put new shoes and wheel cylinders on the back. I did remove the front discs and there was some surface rust on the rotors so we cleaned it off with some emery cloth and they cleaned up nicely. They now look like new after driving it some. The front pads looked like recent installs so we decided to re-use. I checked the run-out of the rotors on the truck and had minimal run-out with my dial indicator. They do not pump back at you when you step on the brakes. I remember a friend's truck years ago, that the front brakes would lock up and I mean lock up and would not release until let set for some time. Turned out to be one of the rubber hoses had collapsed inside. Replaced the hose and "presto" good as new. You know, that is what it feels like down at the bottom of the pedal stroke,,,,its almost as if the power booster quits working,,,,,Hmmm The power Booster either works or doesn't,,,right?

[motornut]

try unplug the booster hose,cover the end with thumb/tape......try the brakes does the idle speed still change?