Hydraulic System Bleeding

When any part of the hydraulic system has been disconnected for service, air may enter the system causing a spongy pedal action. Bleed the hydraulic system after it has been opened to ensure that all air is expelled.

System Priming

When a new brake master cylinder (2140) has been installed or the brake system emptied or partially emptied, fluid may not flow from the bleeder screws during normal bleeding. It may be necessary to prime the system using the following procedure:

1. Use a tubing wrench to remove the brake lines from the brake master cylinder .

2. Install short brake lines in the brake master cylinder and position them so that they point back into the brake master cylinder reservoir (2K478) , and the ends of the pipes are submerged in brake fluid.

3. Fill the brake master cylinder reservoir with new DOT-3 brake fluid.

4. Cover the brake master cylinder reservoir with a shop towel.

    CAUTION: Brake fluid is harmful to painted and plastic surfaces. If brake fluid is spilled onto a painted or plastic surface, immediately wash it with water.

5. Pump the brakes until clear, bubble-free fluid comes out of both brake lines.

6. Remove the short brake lines and reinstall the ones from the vehicle.

7. Bleed each brake line at the brake master cylinder using the following procedure:
   1. Have an assistant pump the brake pedal (2455) 10 times and then hold firm pressure on the brake pedal .
   2. Loosen the rearmost brake line fittings with a tubing wrench until a stream of brake fluid comes out. Have your assistant maintain pressure on the brake pedal until the brake line fitting is tightened again.
   3. Repeat this operation until clear, bubble-free fluid comes out from around the tubing fitting.
   4. Repeat this bleeding operation at the front brake line fitting.

8. If any of the brake lines, or rear disc brake calipers (2552) have been removed, it may be helpful to prime the system by gravity bleeding it. This should be done after the brake master cylinder is primed and bled.

   To prime the brake system:

   1. Fill the brake master cylinder with new DOT-3 brake fluid.
   2. Loosen both rear disc brake caliper bleeder screws and leave them open until clear brake fluid flows out. Be sure to check the brake master cylinder reservoir fluid level often and not let it run dry.
   3. Tighten the wheel cylinder bleeder screws.
   4. One at a time, loosen the rear disc brake caliper bleeder screws. Leave the bleeder screws open until clear fluid flows out. Be sure to check the brake master cylinder reservoir level often and not let it run dry.
   5. Tighten the bleeder screws to 7-9 Nm (61-87 lb-in).

9. After the brake master cylinder has been primed, the lines bled at the brake master cylinder , and the brake system primed, normal brake system bleeding can resume at each wheel.

Manual Bleeding

1. Clean all dirt from brake master cylinder filler cap (2162) .

2. If brake master cylinder is known or suspected to have air in bore, it must be bled before any of the wheel cylinders or rear disc brake calipers . To bleed brake master cylinder , attach drain tube to fitting and submerge free end of tube in container partially filled with clean brake fluid. Loosen upper secondary outlet fitting approximately three-quarter turn.

3. Have assistant push brake pedal down slowly through full travel. Close outlet fitting, then return brake pedal slowly to full-released position. Wait five seconds, then repeat operation until air bubbles cease to appear.

4. Loosen upper primary outlet fitting approximately three-quarter turn.

5. Repeat Step 3.

6. To continue to bleed brake system, remove rubber dust cap from a rear disc brake caliper bleeder fitting.

   Place suitable box wrench on bleeder fitting and attach rubber drain tube to fitting. The end of tube should fit snugly around bleeder fitting.

7. Submerge free end of tube in container partially filled with clean brake fluid and loosen bleeder fitting approximately three-quarter turn.

8. Have assistant push brake pedal down slowly through full travel. Close bleeder fitting, then return brake pedal to full release position. Wait five seconds, then repeat this operation until air bubbles cease to appear at submerged end of bleeder tube.

9. When fluid is completely free of air bubbles, secure bleeder fitting and remove bleeder tube. Install rubber dust cap on bleeder fitting.

10. Repeat this process on opposite rear disc brake caliper . Then, repeat on both front disc brake calipers. Check to ensure that the caliper bleed fitting is positioned on the upper half of the front disc brake caliper. If not, the rear disc brake caliper is on the wrong side.

    Refill brake master cylinder reservoir after each wheel cylinder or rear disc brake caliper is bled, and install brake master cylinder filler cap . When bleeding operation is completed, fluid level should be filled to maximum fill level indicated on brake master cylinder reservoir .

11. Always ensure disc brake pistons are returned to their normal positions by depressing brake pedal several times until normal pedal travel is established.

12. Check pedal feel. If brake pedal feels "spongy", repeat bleed procedure.

Pressure Bleeding

For pressure bleeding, use a bladder-type bleeder tank only, such as the Rotunda Brake Bleeder 104-00064 or equivalent.

Bleed the longest lines first on the system being bled. The bleeder tank should contain enough new brake fluid to complete the bleeding operation. Use Heavy-Duty Brake Fluid C6AZ-19542-AA (ESA-M6C25-A) or DOT-3 equivalent for all brake applications. Never reuse brake fluid that has been drained from the hydraulic system. The pressure bleeder tank should be charged with approximately 69-206 kPa (10 to 30 psi) of air pressure.

 CAUTION: Never exceed 344 kPa (50 psi) pressure.

1. Clean all dirt from the brake master cylinder filler cap .

2. Remove the brake master cylinder filler cap . Fill the brake master cylinder reservoir with the specified brake fluid. Install the pressure bleeder adapter tool to the brake master cylinder , and attach the bleeder tank hose to the fitting on the adapter. Follow the instructions of the manufacturer to install the adapter.

3. If the rear disc brake calipers are to be bled, start with RH rear disc brake caliper and attach bleed tube snugly around bleeder fitting.

4. Open the valve on the bleeder tank to admit pressurized brake fluid into the brake master cylinder reservoir .

5. Submerge the free end of the tube in a container partially filled with clean brake fluid, and loosen the bleeder fitting.

6. When air bubbles cease to appear in the fluid at the submerged end of the bleeder tube, close the bleeder fitting. Remove the tube. Replace rubber dust cap on bleeder screw.

7. Repeat Steps 3 through 6 at rear disc brake caliper .

8. Attach a bleed tube to front brake caliper bleed screws and repeat Steps 4 through 6, starting at RH front wheel caliper and ending at LH front wheel caliper.

9. When the bleeding operation is completed, close the bleeder tank valve and remove the tank hose from the adapter fitting.

10. After disc brake service, ensure disc brake pistons are returned to their normal positions and the shoe and lining assemblies are properly seated. This is accomplished by depressing the brake pedal several times until normal pedal travel is established.

11. Remove the pressure bleeder adapter tool from brake master cylinder . Fill the brake master cylinder reservoir . Install the brake master cylinder filler cap .