Antilock Brake System Bleeding Procedures

Fig 2 Extending Valve Stem:

NOTE: All vehicles are equipped with a pressure hold-off valve. The valve is located (in the combination valve) on the left frame rail. The hold off valve balances front and rear braking force to improve braking and steering control on icy surfaces. The valve shuts off the flow of brake fluid between 3 and 135 PSI. Because the valve shuts off flow in this pressure range the valve must be held open manually -- using tool C-4121 or equivalent -- when pressure bleeding the system.

CAUTION: Under no circumstances should a rigid clamp, wedge or block be used to depress the valve stem. This could cause an internal valve failure resulting in complete loss of front brakes.

1. Clean all dirt and foreign material from the cover of the master cylinder to prevent dirt from falling into the master cylinder reservoir when the cover is removed.
2. Install metering valve hands off tool, part No. C-4121 to valve stem of metering valve.

NOTE: Complete bleeding of dual master cylinder is important before performing this procedure!

3. Starting with RWAL hydraulic valve, clean all dirt from the bleeder valve.
4. Place bleeder hose on the bleeder valve and insert the other end of the bleeder hose into a clear jar half filled with clean brake fluid. This will permit the observation of air bubbles as they are being expelled from the hydraulic system and also prevent air from being drawn back into the system.
5. Continue this bleeding with:
a. The right rear wheel
b. Then left rear wheel
c. Next, bleed the right front and
d. Finish with the left front wheel
6. Repeat this bleeding procedure if there is any indication of air remaining in the hydraulic system:
- Spongy brake pedal
- Warning light ON

CAUTION: The pressure release valve is in its innermost position when there is no pressure present. No attempt should be made to further depress the valve stem.

NOTE: If diagnosis determines that master cylinder alone is cause of trouble, it can be replaced without bleeding the hydraulic system provided the replacement cylinder is completely bled before installation. After brake tubes are connected have helper apply force to pedal while both tube nuts are cracked to release any air and then retightened.