Brake Bleeding - soft pedal - ABS


Ralph50
09-06-2015, 11:06 PM
I replaced the rear brake line on my 2000 GMC Jimmy 4dr-4WD.
The job went ok, the lines over the axle are on right side - pass - is a 3/16 inch x 30 inch long. The left - driver - is same 3/16 but actual is 15 inch but auto store does not have this length so 12 inch just barely fits. I also replaced the hose that is towards the left side of axle and goes from frame to axle bracket. The line on the top side of this hose is a 1/4 inch brake line. This line then goes forward to the ABS module, as seeing from the front left fender the line is top far left as you look towards the engine leaning over the fender. To adapt to the ABS module you need a short piece of 1/4 line that has 1/4 inch on one end and the other has a fitting that fits into a 1/2 inch thread, see autozone.
So now the problem. Bleeding this vehicle is a real problem. So many complaints on the net. Using the petal push and hold does not work. My opinion why. The 1/4 line goes from up high to down to the frame about 20 inches down. Problem is when you push the brake pedal there is not enough movement of fluid to keep the air bubble moving towards the rear, so after the pedal is pushed the air bubble moves back up, remember air rises. The best way is to power bleed, so the air keeps moving towards the rear bleed screws. Its because of the 1/4 inch line, 3/16 lines, the air bubble is smaller and moves in the line. So I rigged up a pressure bleed with a steel nipple glued to a hole in the brake fluid cap and o ring pressurized to 30psi and opened the rear bleed screw and out came the bubbles. Others say a vaccum attached to the bleed screw also works. Make sure, very important, do not let the reservoir do empty. The key is that the fluid moves fast and keeps moving, something pushing the pedal does not do, I would guess one push of the pedal moves 10 inces in the 1/4 inch line. This is not enough.

Ralph50
09-06-2015, 11:15 PM
Found the ABS bleeding is also a problem. I watched a u tube video on how easy bleeding of the ABS is. But the problem is finding a cheap scan tool that has the bi-directional capability to bleed brakes. The lowest price I found is 300 dollars. Its a simple switching on and off the ABS while pushing the brakes, but cant find a simple cheap one. I found on internet some tool that pushing a pin in on the ABS module that is supposed to make bleeding the unit easier, it is probably something the assembly plant uses to bleed the system.

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