Hydraulic System Bleeding

Manual Bleeding
Pressure bleeding is recommended for all non-ABS hydraulic systems. However, if a pressure bleeder is unavailable, use the following procedure. Brake fluid damages painted surfaces. Immediately clean any spilled fluid.

1. Remove vacuum reserve by pumping brakes several times with engine off.
2. Fill master cylinder reservoir with clean brake fluid. Check fluid level often during bleeding procedure; do not let reservoir fall below half full.
3. If necessary, bleed master cylinder as follows:
a. Disconnect master cylinder forward brake line connection until fluid flows from reservoir. Reconnect and tighten brake line.
b. Instruct an assistant to slowly depress brake pedal one time and hold.
c. Crack open front brake line connection again, purging air from cylinder.
d. Retighten connection and slowly release brake pedal.
e. Wait 15 seconds, then repeat until all air is purged.
f. Bleed the rearward (nearest the cowl) brake line connection by repeating steps a through e.
4. Loosen, then slightly retighten bleeder valves at all four wheels. Repair any broken, stripped or frozen valves at this time.
5. Proceed to appropriate wheel first and follow set sequence according to the bleeding sequence.

Bleeding Sequence: RR-LF-LR-RF

Fig. 20 Bleeding Brakes:

6. Place transparent tube over bleeder valve, then allow tube to hang down into transparent container, Fig. 20. Ensure end of tube is submerged in clean brake fluid.
7. Instruct an assistant to slowly depress brake pedal one time and hold.
8. Crack open bleeder valve, purging air from cylinder. Retighten bleeder screw and slowly release pedal.
9. Wait 15 seconds, then repeat steps 7 and 8. Repeat these steps until all air is bled from system.

Fig. 21 Installing Pressure Bleeder Adapter:

Fig. 20 Bleeding Brakes:

Pressure Bleeding, Non-ABS Only
1. Loosen, then slightly retighten bleeder valves at all four wheels. Repair any broken, stripped or frozen valves at this time.
2. Using a diaphragm type pressure bleeder, install suitable bleeder adapter to master cylinder, Fig. 21.
3. Charge bleeder ball to 20-25 psi.
4. Connect pressure bleeder line to adapter.
5. Open line valve on pressure bleeder, then depress bleed-off valve on adapter until a small amount of brake fluid is released.
6. Raise and support vehicle.
7. Proceed to appropriate wheel first and follow set sequence according to Wheel Bleeding Sequence.
8. Place transparent tube over bleeder valve, then allow tube to hang down into transparent container, Fig. 20. Ensure end of tube is submerged in clean brake fluid.
9. Open bleeder valve 1/2 to 3/4 turn and allow fluid to flow into container until all air is purged from line.

Wheel Bleeding Sequence
Rear wheel drive models except Corvette: if manual bleeding, RR-LR-RF-LF; if pressure bleeding, bleed front brakes together and rear brakes together.
Front wheel drive models except Spectrum: RR-LF-LR-RF.
1989 Corvette: RF-RR-LR-LF.
Spectrum: LF-RR-RF-LR.

Flushing Hydraulic System
If brake fluid is old, rusty or contaminated, or whenever new parts are installed in hydraulic system, the system must be flushed. Bleed brakes, allowing at least one quart of clean brake fluid to pass through system. Any rubber parts in hydraulic system which were exposed to contaminated fluid must be replaced.