Originally Posted by MouseFink
You must bleed the ABS modulator then bleed the brakes in the usual manner. You cannot bleed the ABS modulator without cycling it with a GM Tech 1 scan tool. Those scan tools can be found on e-bay for $300 to $400. You also need two OTC 7853 proportioning valve depressor clamps to use on the ABS modulator accumulator valves as the ABS unit is cycled. If you do not correctly bleed the ABS modulator, you can pressure bleed or foot pump ten gallons of fluid through the system and never get any brake pedal.
The shade tree method of bleeding the ABS modulator is to get on a gravel road and get up to 50 or 60 MPH and slam on the brakes and slide the tires. That may cycle the ABS modulator. The problem with that is it takes guts to get up to 50 or 60 MPH on a dirt road without any brakes.
IT WAS A BAD ABS HYDRAULIC UNIT