The Kelsey-Hayes 4WAL ABS system has been used on many GM light trucks through the years. So chances are pretty good you’ll tangle with one real soon. Like all ABS, the 4WAL system is designed to keep the vehicle under control during heavy braking. To meet this challenge, however, there may be...
www.motor.com
Bleeding the BPMV is rather complex on the Kelsey-Hayes 4WAL system. A pressure or vacuum bleeder is preferred over using the brake pedal for this procedure. If the pedal must be used, consider removing the master cylinder to clean the reservoir, then bench bleed it to flush out any debris. If a new master cylinder is being installed, be sure to bleed it before installation. When vacuum or pedal bleeding, don't let the master cylinder reservoir run dry! Once air is bled from the master cylinder, the BPMV can be bled as follows:
1. Open the internal bleed screws a quarter- to a half-turn. These are the cap screws on either side of the BPMV.
2. Attach special tools (Kent-Moore No. J39177) to hold open the high-pressure accumulator bleed valves.
3. Open the two bleeder screws at the BPMV and bleed the unit.
4. Bleed the wheels in the following order: right rear, left rear, right front, left front.
5. Retighten the internal bleed screws and remove the tools from the high-pressure accumulators.
6. Firmly depress the brake pedal and perform three to six functional tests using either a scan tool or the jumper method described earlier. This forces remaining air from the BPMV into the lines running to the wheels.
7. Finally, bleed all four wheels again in the following order: right rear, left rear, right front, left front, to remove any air that was expelled from the BPMV. Note: This procedure should be necessary only if the BPMV is being replaced. During routine service, the system can be bled normally at the wheels.