REMOVAL & INSTALLATION
- Disconnect the hydraulic line(s) at the master cylinder.
- Remove the two retaining nuts and lockwashers that hold the cylinder to the firewall or vacuum booster.
On 1967 and later models, disconnect the pushrod at the brake pedal.
- Remove the master cylinder, gasket, and rubber boot.
- Position the master cylinder on the firewall, making sure the pushrod goes through the rubber boot into the piston.
On 1967 and later models, reconnect the pushrod clevis to the brake pedal.
- Install the nuts and lockwashers.
- Install the hydraulic line(s), then check brake pedal free-play.
- Bleed the brakes as described later in this section.
Cars having disc brakes do not have a check valve in the front outlet port of the master cylinder. If one is installed, front disc will immediately wear out due to residual hydraulic pressure holding the pads against the rotor.
- Remove the master cylinder from the vehicle.
- Secure the master cylinder in a vise and remove the pushrod assembly and protective boot. This exposes the lockring 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 denatured alcohol.
- Carefully inspect the washed metal parts and the cylinder bore. A corroded cylinder must be replaced. Discoloration or stains can be removed with crocus cloth. When doing this, wrap the cloth around your finger and rotate the cylinder around the cloth.
- To reassemble, moisten the cylinder bore with brake fluid and replace the valve seat, valve assembly, and spring.
- Moisten the primary cup with 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 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 pushrod, and install the master cylinder.
- Attach the brake pedal clevis and adjust the pushrod-to-piston clearance. Correct adjustment calls for a barely perceptible free pedal before piston/pushrod contact.
Overhaul of power brake master cylinders is the same as that for manual brake master cylinders.
- Bleed the brake system.
- Remove the master cylinder from the car.
- Remove the mounting gasket and boot, and also the main cover, then purge the fluid from the unit.
- Secure the cylinder in a vise and remove the pushrod 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 retainer from the bore of the cylinder. An alternate method is to use hooked wire 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 end of the screw with a claw hammer and pry the insert free.
- An alternate way of removing 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, and then thread at 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 parts. Slight rust may be removed with 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 flat end of the piston.
- Slip the primary seal and its protector over the end of the secondary piston opposite the secondary seals. The flat side of this seal should face the piston's compensating hole flange.
- Replace the primary piston assembly with the assembled piece in the overhaul kit.
- Moisten the cylinder bore and the secondary piston's inner and outer seals with brake fluid. Assemble the secondary piston spring to its retainer and position them over the end 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 brake fluid and push it-pushrod 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 torque it to 25-40 inch lbs.
- Replace the reservoir diaphragm and cover.
Overhaul of the main cylinder portion of power brake master cylinders is the same as that for manual brake master cylinders.
- Install the master cylinder, then bleed the brake system.