General Service Procedures
1991
06-06-4 Hydraulic Brake System 06-06-4
GENERAL SERVICE PROCEDURES
Hydraulic System Flushing
NOTE: The hydraulic system must be flushed if there is any doubt about the grade of the fluid in the system or if the system is suspected of containing even a trace of mineral oil. If the system has been contaminated with any petroleum product or mineral oil, all seals and hoses must be replaced.
1. Fill the master cylinder reservoir with clean DOT-3 brake fluid.
2. Using a six point box wrench, loosen and then tighten all four bleeder screws.
3. Attach a length of rubber hose to each bleeder screw and place the free end of each hose in a suitable container filled with clean brake fluid. The hose must fit snugly on the bleeder screw.
4. Open all four bleeder screws.
5. Pump the brake pedal until the brake fluid is removed from the hydraulic system.
^ As the system empties brake fluid, allow the brake pedal to return before repeating a pump stroke.
6. Close the bleeder screws on the wheel cylinders.
7. Spread the brake pads on both front calipers using Disc Brake Pad Spreader D79L-2196-A, or equivalent.
8. While leaving the spreader tools in place, continue pumping the brake pedal until only air is being pumped out of the brake caliper bleeder screws.
9. Open the bleeder screws at the wheel cylinders.
10. Close the bleeder screws on the calipers.
11. Fill the master cylinder with DOT-3 brake fluid.
12. Alternately pump the brake pedal and fill the master cylinder until clean brake fluid is pumped into the containers at the wheel cylinders.
13. Close the wheel cylinder bleeder screws.
14. Open the caliper bleeder screws.
15. Place the bleed tubes from the caliper in glass jars containing a small quantity of approved brake fluid.
^ Position the jar at least 300 mm (12 inch) above
the bleeder screws. This is to ensure that the
bleeder screws have fluid around them at all
times, thereby preventing air from leaking past
the threads of the bleeder screws and into the
system.
16. Alternately pump the brake pedal and fill the master cylinder reservoir until clean, air-free brake fluid is pumped into the jars at the caliper.
17. With the brake pedal fully depressed, close the caliper bleeder screws.
18. Top off the reservoir with new fluid as required.
19. Remove the caliper spreaders and depress the brake pedal to move the caliper pistons to the fully extended position.
20. With the pedal still depressed, open the caliper bleeder screws.
21. Force the piston back to its fully retracted position with Caliper Spreaders D79L-2196-A, or equivalent, and close the caliper bleeder screws.
22. Remove the caliper spreaders.
23. Bleed the entire brake system. If necessary, refer to the procedure in this Section.
1991
06-06-5 Hydraulic Brake System 06-06-5
GENERAL SERVICE PROCEDURES (Continued)
Hydraulic System Bleeding
When any part of the brake hydraulic system has been disconnected for service, air will enter the system and cause spongy pedal action. To remove the air, the system must be bled using either pressure bleeding equipment Rotunda Model 104-00064 or equivalent, or the manual method. If only one system has been opened, normal pedal feel can usually be restored by bleeding only the opened system. Don't forget that this vehicle uses a diagonally-split system. The left front and right rear are on one brake circuit while the right front and left rear are on another brake circuit. When bleeding brakes, go to the rear brake first and then the front caliper on the same circuit. This will ensure that the longest line in either system is being bled first.
System Priming
When a new master cylinder 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. Using a tubing wrench, remove the brake lines from the master cylinder.
2. Install short brake lines in the master cylinder and position them so that they point back into the reservoir and the ends of the pipes are submerged in brake fluid.
3. Fill the reservoir with new DOT-3 brake fluid.
4. Cover the reservoir with a shop towel.
5. Pump the brakes until clear, bubble-free fluid comes out of both brake lines. If any brake fluid spills on the paint, wash it off immediately with water.
6. Remove the short brake lines and reinstall the ones from the vehicle.
7. Bleed each brake line at the master cylinder using the following procedure:
a. Have assistant pump the brake pedal 10 times and then hold firm pressure on the pedal.
b. Crack the rear most brake line fittings with a tubing wrench until a stream of brake fluid comes out. Have assistant maintain pressure on the brake pedal until the brake line fitting is tightened again.
c. Repeat this operation until clear, bubble-free fluid comes out from around the tubing fitting.
d. Repeat this bleeding operation at the front brake line fitting.
8. If any of the brake lines, calipers, or wheel cylinders have been removed, it may be helpful to prime the system by gravity bleeding it. This should be done after the master cylinder is primed and bled.
To prime the brake system:
a. Fill the master cylinder with new DOT-3 brake fluid.
b. Loosen both wheel cylinder bleeder screws and leave them open until clear brake fluid flows out. Be sure to frequently check the reservoir fluid level and not let it run dry.
c. Tighten the wheel cylinder bleeder screws.
d. One at a time, loosen the caliper bleeder screws. Leave the bleeder screws open until clear fluid flows out. Be sure to frequently cheek the reservoir level and not let it run dry.
e. Tighten the bleeder screws.
NOTE: Since front-wheel drive cars do not normally use hold-off valves, this method works on all four wheels.
9. After the master cylinder has been primed, the lines bled at the master cylinder, and the brake system primed, normal brake system bleeding can resume at each wheel.
Manual Bleeding
1. Clean all dirt from the master cylinder filler cap.
2. If the master cylinder is known or suspected of having air in the bore, it must be bled before any of the wheel cylinders or calipers are bled. To bleed the master cylinder, follow the procedures described in this Section.
3. To bleed the wheel cylinders and calipers, proceed as follows:
a. Begin at the rear bleeder screw.
b. Attach a rubber drain hose to the bleeder screw. The end of the tube should fit snugly around the end of the bleeder screw.
1991
06-06-6 Hydraulic Brake System 06-06-6
GENERAL SERVICE PROCEDURES (Continued)
c. Place the free end of the hose in a container partially filled with clean brake fluid.
d. Have assistant pump the brake pedal 5-10 times and maintain pressure on the pedal after the last stroke.
e. Loosen the bleeder screw approximately 3/4 turn. It is very important that the helper maintain constant pressure on the pedal until the pedal drops all the way down and the bleeder screw is closed again. If pedal pressure is released, air will be drawn back into the system.
f. Tighten the bleeder screw.
g. Repeat this operation until the fluid is clear and air bubbles no longer appear at the submerged end of the rubber hose.
h. Repeat these steps at the other wheel cylinder and calipers.
NOTE: Never reuse brake fluid.
Pressure Bleeding
CAUTION: Never use copper tubing because copper is subject to fatigue, cracking, and corrosion which could result in brake failure. Use double-walled steel tubing only. To replace a brake tube, use the general procedure outlined below.
1. Obtain the recommended tubing and steel fitting nuts of the correct size. (Outside diameter of tubing is used to specify size.)
NOTE: All tubing fittings used on this vehicle are metric.
2. Cut the tubing to length. Correct length may be determined by measuring the old tubing using a cord and then adding 3 mm (1/8 inch) for each double flare.
3. Make sure the fittings are installed before starting a flare.
^ Double flare all tubing ends using suitable flaring tool. Follow instructions included in the tool set.
NOTE: Double flaring tools must be used, as single flaring tools cannot produce a flare strong enough to hold the necessary pressure.
4. Bend the pipe assembly to match the old pipe using a tubing bender. Clearance of 6 mm (3/4 inch) must be maintained at all moving or vibrating parts.