When any part of the hydraulic system has been disconnected for repair or replacement, air may get into the lines and cause spongy pedal action (because air can be compressed and brake fluid cannot). To correct this condition, it is necessary to bleed the hydraulic system so to be sure all air is purged.
When bleeding the brake system, bleed one brake cylinder at a time, beginning at the cylinder with the longest hydraulic line (farthest from the master cylinder) first. ALWAYS Keep the master cylinder reservoir filled with brake fluid during the bleeding operation. Never use brake fluid that has been drained from the hydraulic system, no matter how clean it is.
The primary and secondary hydraulic brake systems are separate and are bled independently. During the bleeding operation, do not allow the reservoir to run dry. Keep the master cylinder reservoir filled with brake fluid.
On 1990 models equipped with the Teves Mk II ABS system, depressurize the ABS accumulator using the following procedure:
- With the ignition OFF , pressure switch disconnected, pump motor disconnected or the negative battery cable disconnected, pump the brake pedal a minimum of 25 times using at least 50 lbs. of pedal force each time. A definite change in pedal feel will occur when the accumulator is discharged.
- When a definite increase in pedal effort is felt, stroke the pedal a few additional times to remove all hydraulic pressure from the system.
- Clean all dirt from around the master cylinder fill cap, remove the cap and fill the master cylinder with brake fluid until the level is within 1 / 4 in. (6mm) of the top edge of the reservoir.
- Clean the bleeder screws at all 4 wheels. The bleeder screws are located on the back of the brake backing plate (drum brakes) and on the top of the brake calipers (disc brakes).
Bleed the system in the following sequence:
- Attach a length of rubber hose over the bleeder screw and place the other end of the hose in a glass jar, submerged in brake fluid.
- Open the bleeder screw 1 / 2 - 3 / 4 turn. Have an assistant slowly depress the brake pedal.
- Close the bleeder screw and tell your assistant to allow the brake pedal to return slowly. Continue this process to purge all air from the system.
- When bubbles cease to appear at the end of the bleeder hose, close the bleeder screw and remove the hose. Tighten the bleeder screw to the proper torque:
- Check the master cylinder fluid level and add fluid accordingly. Do this after bleeding each wheel.
- Repeat the bleeding operation at the remaining 3 wheels.
- Fill the master cylinder reservoir to the proper level.