brake EXPERT needed...

As you will find in my other posts here, I am having major brake issues with my 1989 GMC C1500 ext cab pickup. Please take a moment to read over my post entitled "1989 GMC Sierra...brake issues". I am in dire need of someone to assist me with this problem.

I have bypassed the entire ABS system on my truck and have ran the brake lines straight from the master cylinder to the wheels, front and back. My problem is the back brakes are loosing pressure somewhere causing the brake pedal to drop 3/4 the way to the floor. I have replaced both wheel cylinders, master cylinder and adjusted the "drag" for the drums on the rear as well. I have checked EVERYTHING for leaks and have found none anywhere.

Is it possible that there is still air in the rear lines? How many fluid ounces does the complete "rear" lines hold?

Please help......thanx all.

I just got done pumping another 32 fl oz through the rear only, and I am still hearing/seeing air from the rear. This makes almost 128 fl oz of brand new brake fluid that I have thrown away on the rear brakes alone. Both rear wheel cylinders are brand new and show no evidence of leakage and all lines from the master cylinder to the rear wheels are clean with no evidence of leakage.

If I pump the brakes a few times with the truck running or not, they will get slightly stiffer with a couple inches more of brake pedal. But if I let it sit for just a few seconds with the truck running or not, the pedal will drop "easily" 3/4 the way to the floor.

There is obviously air in my rear lines, but with no evidence of leakage and all brand new parts, where is the air coming from?

did you check for wore hoses, they will expand when they are weak.
try clamping the brake hoses off( all three). Apply brakes (peddle should be hard,of not bad master cylinder).Release pass front clamped hose (apply brakes peddle should be hard,if not bad calipier). continue releasing clamps one at a time until you have soft peddle.that is where the problem will be. Hope this helps.