Bleeding 4wheel Antilock brake system 94 S-10

[rouser]

Greetings:

I need some info on how to do a complete brake bleeding for my 1994 S-10 with 4 Wheel Antilock brake system. that autozone.com called the EBCM system.

I recently had to replace the master cylinder on the vehicle because the brakes got spongy and tearing the master cylinder apart revealed scoring on the piston wall and a o-ring seal that was flat on one side and I did bench bleed the master cylinder before re-installing it on the truck to verify no air in the master cylinder..

Since this was the first vehicle I owned with antilock brakes, I did not realize that the Brake pressure Modulator valve could hold air inside of it. I have had brake failure approximately six times and everytime. I did a individual wheel brake bleed to find air on one or both of the rear wheels. to which I was able to get out and then tap off the master cylinder resevoir.

I have tried looking online for instructions on how to bleed the air out of the Brake pressure Modulator valve to no avail. I went to an automobile internet mechanics chat and when I mentioned my vehicle and the 4 wheel antilock brakes, he laughed and told me to let GM do the job and that the system was flawed from the inception and eventually was replaced with a fixed system for all 1996 S-10's.



I have been told that to bleed the brakes properly, that all 4 bleeders must be open with 4 people there with jars with brake fluid present while one mashes the brakes slowly to where fluid gushes out of all wheel cylinders at the same time and a fifth person present to tap off the master cylinder resevoir.

I have tried bleeding the brakes approx 8 times with the RR-LR-RF-LF pattern and have gotten air out and a tight brake petal feel to only have to repeat this approx a couple of weeks later. I have retested the replaced master cylinder and took it apart and see if any signs of scoring or a bad o-ring seal and do not see it.

I'm now at the point of believing that the Brake Pressure Modulator Valve is holding air and I want to know how to bleed it. I have even tried to with flare nut wrenches to loosen about 1/16th a turn the three outlet tubes (2 to the front wheels and 1 to the rear wheels) to see if air bleeded out to no avail. There are also two 'pressure valve' looking devices on the top of the Brake pressure Modulator valve that I have loosened 1/16th of a turn to no avail.

Has anyone here ever had this problem and figured out to fully bleed the system? I am getting baffled now.

[GMMerlin]

There is a special tool (actually you will need three of them) to depress valves on the EBCM and the proportioner valve to property bleed the brake system...also may need a Tech 1 to run the autobleed procedure and ABS function tests.