Service Procedures
Service Information
HYDRAULIC SYSTEM FLUSHING/BLEEDING
The 4WAL hydraulic system requires flushing at intervals related to regularly scheduled brake lining replacement. Use one quart of DOT 3 fluid to bleed the existing system fluid from all channel passages. This will remove any moisture which may cause component corrosion.
- NOTE -
Do not use DOT 5 (silicone) brake fluid. System damage may result.
Manual Bleeding
1. Deplete the vacuum reserve by applying the brake, several times.
2. Fill the master cylinder with DOT 3 brake fluid. During bleeding, keep the master cylinder at least one-half full at all times.
3. Bleed the wheel circuits in the following order: left rear, right rear, left front, right front.
4. With the proper box-end wrench over the bleed valve, attach a bleeder tube to the valve. Allow tube to hang, submerged in brake fluid in a clean glass jar (Figure 11-3-72).
5. Fully depress the brake pedal and open the bleeder valve.
6. Close the bleeder valve and release the brake pedal.
7. Repeat steps 5 and 6 until all air has been evacuated from the system. Refill the master cylinder reservoir as necessary to maintain brake fluid level and prevent the entry of air into the hydraulic system.
8. If necessary, repeat the bleeding procedure at any wheel circuit that is to be bled.
9. Check the brake pedal for a "spongy" feeling, and repeat the bleeding procedure as necessary.
- - NOTE -
Install the HPA bleed valve stem depressor tools during hydraulic system bleeding. Also, open the two side bleed screws 1/4- to 1/2-turn. Remove tools and close valves when finished.
Pressure Bleeding
The following procedure refers to the usage of Kent-Moore Diaphragm Brake Bleeder J-29532 or its equivalent (Figure 11-3-73):
1. Install the correct bleeding adapter to the master cylinder.
2. Ensure that the pressure bleeder fluid tank is at least one-third full of Delco Supreme # 11 brake fluid, or its DOT 3 equivalent.
3. Charge the pressure bleeder air tank to between 20 and 25 psi (140 to 175 kPa).
4. Attach the hose to the master cylinder bleeder adapter and open the pressure tank fluid valve.
5. Bleed the wheel circuits in the following order: left rear, right rear, left front, right front.
6. With the proper box-end wrench over the bleeder valve, attach a bleeder tube to the valve. The discharge end of the bleeder tube must be submerged in brake fluid in a clean glass jar.
7. Open the bleeder valve at least 3/4-turn and allow fluid to flow until air-free fluid flows from the bleeder tube.
8. Close the bleeder valve; be sure that it is properly sealed.
9. Repeat steps 6 through 8 until all air has been evacuated from the system.
10. Check the brake pedal for a "spongy" feeling, and repeat the bleeding procedure as necessary.
11. Properly dispose of all fluid bled from the brake system.
12. Close the pressure tank fluid valve, and disconnect the bleeding equipment from the brake bleeder adapter.
13. Remove the bleeder adapter from the master cylinder. Clean up any fluid spilled during adapter removal.
14. Fill the master cylinder reservoirs to the proper level.
15. Install the master cylinder diaphragm and cover.
Vacuum Bleeding
1. Connect Vacuum Bleeder 85 00001 to a source of compressed air (Figure 11-3-74).
2. Uncap brake master cylinder reservoir.
3. Depress lever on the top of the bleeder tool to create a vacuum. Use the bleeder hose to vacuum the hold brake fluid out of the reservoir. Release the lever.
4. Fill the master cylinder reservoir with fresh brake fluid of the specified type. Periodically check the reservoir fluid level to avoid running it dry.
5. Clean the bleeder screws and bleed holes if necessary.
6. Connect the vacuum bleeder hose to the bleed screw, and open the bleed screw slightly.
7. Depress the vacuum bleeder lever to create vacuum and begin the bleeding process. Watch the flow of brake fluid; continue bleeding until about 10 seconds after clean fluid flows into bleeder container.
8. Release the vacuum bleeder lever and close the bleed screw.
9. Repeat the procedure as necessary to fully bleed the brake hydraulic system.
10. Check brake pedal for firmness; repeat bleeding procedure as necessary.
11. Check fluid lever in master cylinder, and top up as necessary install, master cylinder reservoir cap.
12. Detach vacuum bleeder from vehicle and shop air source.
- NOTE -
It is normal to observe bubbles or foam in the vacuum hose when using the vacuum bleeder (Figure 11-3-74). This air is drawn into the fluid flow from around the bleed screw threads; it has no effect on bleeding. If desired, apply a small amount of silicone lubricant to the base of the bleed screw to prevent air entry (Figure 11-3-76).