I have a 93 GMC 1/2 ton 350. I have no brakes. I have replaced the calipers on the front, rotors on the front and pads on the front. I also replaced the master cylender and reservoir and flushed the lines. The last thing I replaced was the R side brake hose that goes from the caliper to the brake line. I bled off the system from the rear to the front. With the truck off I get in to pump the brakes and they stiffen up like normal, I pause for 15 seconds and press pedal down and it goes all the way to the floor as if their were alot of air in the system. Then I start the truck and the pedal automatically goes to the floor when pressed, it wont pump up at all. I have checked all the lines / hoses, and calipers and see no wet spots / leaks. I seriously bled the system so much that I went through 5qts of fluid. Do you have any other ideas that I can try?
Based on your description of a good pedal, then it goes to the floor after waiting 15 seconds, it sounds like the rear shoes are out of adjustment. After pressing the pedal once, it will come back up faster than the brake fluid can return from the rear so the shoes are partially applied when you press the pedal again and take a new bite of fluid. The shoes will move out a little further each time you pump the pedal until they contact the drums. That's when the pedal will become firm. When you release the pedal for more than a few seconds that gives the shoes time to fully retract. Then the pedal will go to the floor again.
JUS 10 TIME
March, 22, 2011 AT 2:42 AM
Hey thanks for the reply, I actually figured it out the very next day. Believe it or not, I actually had to take the calipers back off, remove the pads and bench bleed each caliper 3 times. I have done a hundred brakes, and NEVER had to do that before. For some reason the fluid wasnt pushing all the air out of the bleed valve. So that is now a NOTE TO SELF.
March, 22, 2011 AT 3:11 AM
Happy to hear it's fixed. Any chance the calipers were on the wrong side putting the bleeder screws on the bottom? Sounds silly but that's what someone else found a few weeks ago.