REMOVAL & INSTALLATION - Drum Brakes
See Figures 1, 2, 3 and 4
- Disconnect the hydraulic lines from the cylinder. Plug the lines to keep dirt out of the lines and master cylinder.
- Remove the clevis pin and clip from the brake pedal arm.
- Remove the main cylinder-to-firewall nuts and lockwashers, and remove the master cylinder.
- Install the master cylinder on the firewall studs. Install the lockwashers, and tighten the nuts.
- Insert the clevis pin through the clevis and the brake pedal and secure with a new cotter pin.
- Unplug and connect the hydraulic lines to the master cylinder.
- Refill the cylinder with brake fluid and bleed the lines.
- Adjust the brake pedal as necessary.
Disc Brakes1967-82 VEHICLES
The early disc brake master cylinder is serviced in the same manner as the drum brake master cylinder. The later master cylinder is the dual reservoir type. This offers a separate brake circuit for the front and rear wheel pairs and prevents total loss of braking should one circuit fail.
This master cylinder is actually two complete master cylinders contained in a single housing, with the front reservoir controlling the front brake pairs and the rear reservoir, the rear brake line just below the master cylinder.
Be absolutely certain that replacement parts are identified as identical to those being replaced when overhauling the dual master cylinder. The displacement capability of the master cylinder is dependent upon the length of the secondary piston.
OVERHAUL - Drum Brakes
See Figure 5
Overhaul of the main cylinder portion of power brake master cylinders is the same as that for manual master cylinders.
- Secure the master cylinder in a vise and remove the pushrod assembly and the protective boot. This exposes the lock ring which, when removed, allows extraction of the piston stop, secondary cup, and piston.
- Remove the cylinder end plug and push out the primary cup, spring, valve assembly, and seat.
- Wash the component parts with clean alcohol only, and be sure that all traces of gasoline or kerosene are removed. Gasoline will cause premature deterioration of the cylinder rubber parts.
- Carefully inspect the washed metal parts and the cylinder bore. A corroded cylinder must be replaced. Discoloration or stains should be removed with crocus cloth. When doing so, wrap the cloth around a finger and rotate the cylinder around the supported cloth. Do not polish the bore lengthwise as this can cause a fluid leak.
- Check the piston-to-cylinder clearance with a feeler gauge. Clearance should be between 0.001 in. and 0.005 in.
- Moisten the cylinder bore with clean brake fluid and replace the valve seat, valve assembly, and spring.
Be sure that the valve and seat are properly installed before proceeding. An incorrectly assembled check valve will distort and fail to provide a check valve seal, which will result in a reduction of brake pedal travel and a corresponding loss of actual braking.
- Moisten the primary cup with clean brake fluid and install it, flat side out, and seated over the spring. The primary cup is distinguished by a brass support ring at its base.
- Dip the secondary cup in clean brake fluid and slip it over the end of the piston.
- Insert the completed assembly, with the bleeder brake end of the piston installed first. Secure the parts with the piston stop and the snapring, and install the end plug.
- Attach the rubber boot and push rod, and replace the cylinder on the firewall.
- Attach the brake pedal clevis and adjust the push rod-to-piston clearance. Correct adjustment calls for a barely perceptible free pedal before piston/push rod contact.
- Remove the unit from the vehicle using the same general procedure as described for conventional master cylinders.
- Remove the mounting gasket and boot, and the main cover; purge the unit of its fluid.
- Secure the cylinder in a vise and remove the push rod retainer and the secondary piston stop bolt found inside the forward reservoir.
- Compress the retaining ring and extract it along with the primary piston assembly.
- Blow compressed air into the piston stop screw hole to force the secondary piston, spring, and its retainer from the bore of the cylinder. An alternate method uses a piece of wire, hooked on one end, to snag and extract the secondary piston.
- Check the brass tube-fitting inserts and if they are damaged, remove them. Leave undamaged inserts in place.
- If replacement is necessary, thread a 6-32 X 5 / 8 in. self-tapping screw into the insert. Hook the head of the screw with a claw hammer and pry the insert free.
- An alternate way to remove the inserts is to first drill the outlet holes to 13 / 64 in. and thread them with a 1 / 4 in. - 20 tap. Position a thick washer over the hole to serve as a spacer then thread a 1 / 4 in. - 20 X 3 / 4 in. hex head bolt into the insert and tighten the bolt until the insert is freed.
- Use denatured alcohol and compressed air to clean the component parts. Slight rust may be removed with fine crocus cloth.
- Replace the brass tube inserts at this time by positioning them in their holes and threading a brake line tube nut into the outlet hole. Turn down the nut until the insert is seated.
- Check the piston assemblies for correct identification and when satisfied, position the replacement secondary seals in the twin grooves of the secondary piston.
- The outside seal is correctly placed when its lips face the piston flat end. The lips of the inner seal face the piston compensating holes.
- Slip the primary seal and its protector over the secondary seals. The flat side of this seal should face the piston compensating hole flange.
- Replace the primary piston assembly with the assembled component found in the overhaul kit.
- Moisten the cylinder bore and the secondary piston inner and outer seals with new brake fluid. Assemble the secondary piston spring to its retainer and position them over the end of the piston with the retainer inside the lips of the primary seal.
- Insert the combined spring and piston assembly into the cylinder and use a small wooden dowel or pencil to seat the spring against the end of the bore.
- Moisten the primary piston seals with new brake fluid and push it, push rod receptacle end out, into the cylinder.
- Keep the piston pushed in and snap the retaining ring into place.
- Relax the pressure on the pistons and allow them to seek their static positions.
- Replace the secondary piston stop screw and tighten it to 25-40 in. lbs.
- Replace the reservoir diaphragm and cover.