Serious brake problems Need some pro help

unsolved · January 31, 2007

I have a 95 Chevy Tahoe 4x4 1500 - 10" shoes in the rear.

I'll make this as short as I can.

Had soft petal replaced Master, Calipers, Pads (The best Ceramics I could find) Rotors, Drums, Shoes, Spring kits, Wheel Cylinders

and bled to my hearts desire. (Yes I followed the book and manufactured a tool to hold the pin down in the valve)

The brakes were better but not quite what they should be. They never worked like they should even when I bought the truck at 2 yrs old which is why I replaced virtually everything. Recently the petal has dropped a few more inches. Checked for leaks. The only leak I could find was the master leaking a small amount from the front reservoir seal. No visual loss of fluid other than that minute bit. The booster died and loss vacuume which caused the idle to jump when braking along with making them almost completely manual at that point. I replaced the booster and the master again because of the small reservoir leak and replaced the pads because they were about 75% gone. Bled again every way possible. The pedal was still lower than should be and still spongy although the brakes worked better than even when I bought it. Found a bad hub and replaced both along with ABS sensors. (Yes the ABS works) Took the drums off and discovered the axle seals were leaking although I replaced them 2 years ago. Replaced the seals and installed new shoes again. Cleaned backing plates and greased as well as self adjuster. (yes the adjusters are adjusted and I use my E-brake often to keep them adjusted as well as the ebrake from freezing.) Checked Caliper lines for bulging - None found. Even tried clamping the caliper lines and rear line from frame to Axle one at a time to see if I could isolate it to one side but nothing significant. Still low pedal and spongy. I can put it to the floor with minimum effort. I can't begin to tell you how many times Ive bled them starting from the farthest to the closest. Tried gravity and Pressure bleeding. No air and still no good pedal. They actually start to grab immediately now when applying pressure which is good but they still go to the floor if you give enough pressure. They will stop the truck and they do not gradually go down while your holding them.

Gave every inch a close look for leaks and could find none. No fluid loss in the master either. Decided to take it to my uncles shop who also gave everything a close inspection and bled them and said no air found. He's going to use some new scanning tool tomorrow to see if there is air in the ABS and remove it. He actually decided to buy this new tool just to try it on my truck cause it's driving him nuts too. Not sure how anything can scan for air inside the ABS unit but It's worth a try. Ive never had this problem on any vehicle and it's driving me nuts. The only things I haven't replaced are the ABS Unit, the apportioner valve and the lines (Which don't leak nor bulge). Is there like a diaphram or something of the sort in the ABS unit or the apportioning valve that could be soft and expanding causing this?

I would imagine it has to be something thats exceptionally bad given the fact I can put the pedal to the floor with minimal effort. I'm fresh out of Ideas here and my uncle isn't cheap but neither is an ABS module.

Any ideas = Greatly appreciated!

bobcat5544 · January 31, 2007

1ST OFF I DIDN'T SEE YOU MENTIONING BLEEDING THE MASTER CYLINDER BEFORE PUTTING IT BACK ON YOUR TRUCK. IF YOU DID NOT DO THIS THEN YOU MAY STILL HAVE AIR IN THE MASTER CYLINDER OR HAVE PUT AIR IN THE SYSTEM AND IF YOU HAVE REPLACED IT TWICE ALREADY THEN YOU HAVE PUT EVEN MORE AIR IN THE SYSTEM. SO IT WOULD TAKE A LOT OF BLEEDING.

2ND USING THE SCANNER TO SEE HOW MUCH AIR IS IN THE SYSTEM, THIS IN NOT POSSIBLE. THE ONLY THING THE SCAN WILL DO IT ACTIVATE THE ABS MODULE AND PUMP TO BLEED OUT ANY AIR IN THE PUMP; IT TAKES A COUPLE OF TIMES TO DO IT. THEN YOU HAVE TO REBLEED THE SYSTEM.

3RD WHEN YOU WERE REPLACING THE MASTER CYLINDER DID YOU CHECK THE LENGTH AND/OR ADJUST THE PUSH ROD THAT GOES BETWEEN THE BOOSTER AND MASTER CYLINDER

4TH IF THE REAR BRAKES ARE NOT ADJUSTED CORRECTLY THEN YOU WILL GET A LOW PEDAL.