Master cylinder — removal, installation and reservoir/grommet replacement
Removal
Note: With the engine off, pump the brake pedal several times to deplete the vacuum in the power brake booster.
1. Remove the air filter housing cover (see Fuel and exhaust systems).
2. Unplug the electrical connector for the fluid level warning switch (see illustration).
i. 2 Master cylinder mounting details
A Electrical connector
B Brake line fittings
C Mounting nuts
3. Remove as much fluid as possible from the reservoir with a suction gun, large syringe or a poultry baster.
Warning: If a poultry baster is used, never again use it for the preparation of food.
4. Place rags under the fittings and prepare caps or plastic bags to cover the ends of the lines once they’re disconnected.
Warning: Brake fluid will damage paint. Cover all body parts and be careful not to spill fluid during this procedure. Loosen the fittings at the ends of the brake lines where they enter the master cylinder. To prevent rounding off the flats, use a flare-nut wrench, which wraps around the fitting hex.
5. Pull the brake lines away from the master cylinder and plug the ends to prevent contamination.
6. Remove the two nuts attaching the master cylinder to the power booster. Pull the master cylinder off the studs to remove it. Again, be careful not to spill the fluid as this is done. Remove and discard the old gasket between the master cylinder and the power brake booster. Also check the 0-ring on the end of the master cylinder, replacing it if it is cracked or hardened.
Installation
Note: Before installing a new or rebuilt master cylinder, check the clearance between the booster pushrod and the pocket in the master cylinder piston. If necessary, adjust the length of the power brake booster pushrod (see Power brake booster — check, removal and installation).
7. Bench bleed the master cylinder before installing it. Because it will be necessary to apply pressure to the master cylinder piston and, at the same time, control flow from the brake line outlets, it is recommended that the master cylinder be mounted in a vise, with the jaws of the vise clamping on the mounting flange.
8. Attach a pair of bleeder tubes (available at most auto parts stores) to the outlet ports of the master cylinder (see illustration).
i. 8 The best way to bleed air from the master cylinder before installing it on the vehicle is with a pair of bleeder tubes that direct brake fluid into the reservoir during bleeding
9. Fill the reservoir with brake fluid of the recommended type (see Tune-up and routine maintenance).
10. Slowly push the pistons into the master cylinder (a large Phillips screwdriver can be used for this) — air will be expelled from the pressure chambers and into the reservoir. Because the tubes are submerged in fluid, air can’t be drawn back into the master cylinder when you release the pistons.
11. Repeat the procedure until no more air bubbles are present.
12. Remove the bleed tubes, one at a time, and install plugs in the open ports to prevent fluid leakage and air from entering. Install the reservoir cap.
13. Install the master cylinder over the studs on the power brake booster and tighten the nuts only finger-tight at this time. Don’t forget to use a new gasket.
14. Thread the brake line fittings into the master cylinder. Since the master cylinder is still a bit loose, it can be moved slightly so the fittings thread in easily. Don’t strip the threads as the fittings are tightened.
15. Tighten the mounting nuts to the torque listed in this Chapter’s Specifications. Tighten the brake line fittings securely.
16. Plug in the electrical connector to the fluid level warning switch.
17. Fill the master cylinder reservoir with fluid, then bleed the master cylinder and the brake system (see Brake hydraulic system — bleeding). To bleed the master cylinder on the vehicle, have an assistant depress the brake pedal and hold it down. Loosen the fitting to allow air and fluid to escape (see illustration). Tighten the fitting, then allow your assistant to return the pedal to its rest position. Repeat this procedure on both fittings until the fluid is free of air bubbles. Check the operation of the brake system carefully before driving the vehicle.
i. 17 Have an assistant depress the brake pedal and hold it down, then loosen the fitting nut, allowing the air and fluid to escape; repeat this procedure on both fittings until the fluid is clear of air bubbles
Reservoir/grommet replacement
Note: The brake fluid reservoir can be replaced separately from the master cylinder body if it becomes damaged. If there is leakage between the reservoir and the master cylinder body, the grommets on the reservoir can be replaced.
18. Remove as much fluid as possible from the reservoir with a suction gun, large syringe or a poultry baster.
Warning: If a poultry baster is used, never again use it for the preparation of food.
19. Place rags under the master cylinder to absorb any fluid that may spill out once the reservoir is detached from the master cylinder.
Caution: Brake fluid will damage paint. Cover all body parts and be careful not to spill fluid during this procedure.
20. Remove the screw that retains the reservoir to the master cylinder.
Note: A roll pin is used to retain the reservoir to the master cylinder that must be driven out with a hammer and a punch.
21. Pull the reservoir out of the master cylinder body.
22. Pull the grommets out of the master cylinder (see illustration).
i. 22 After the reservoir has been removed, pull the grommets from the master cylinder body; if they’re hard, cracked or damaged, or have been leaking, replace them
23. Lubricate the new grommets with clean brake fluid, then press them into place.
24. Push the reservoir into the grommets and secure it with the screw.
25. Refill the reservoir with the recommended brake fluid (see Tune-up and routine maintenance) and check for leaks.
26. Bleed the master cylinder, followed by the remainder of the system (see Brake hydraulic system — bleeding).