Master Cylinder

NOTE: Operation of the servo when the master cylinder is not in place can cause its mechanism to travel past its normal limit; this can damage the servo beyond repair.

Before the master cylinder is removed, press and release the brake pedal at least 10 times. This is to be sure that no vacuum exists to operate the servo.

REMOVE
1. Peel cover from brake fluid reservoir cap and disconnect wires from fluid level indicator.
2. Remove reservoir cap and filter.
3. Using suitable syringe remove brake fluid from reservoir.
4. Remove clips securing hoses to master cylinder adaptors, use waste rag to collect remaining fluid from feed pipes.
5. Disconnect brake pipes from master cylinder outlet unions, plug pipes to prevent loss of fluid and ingress of dirt.
6. Remove nuts securing master cylinder to servo unit, lift master cylinder from mounting studs.

DISASSEMBLE
1. Carefully pry reservoir hose adaptors from sealing grommets.
2. Using suitable screwdriver lever sealing grommets from master cylinder.
3. Press primary piston into bore of cylinder and withdraw secondary piston stop pin from forward grommet housing.
4. Remove circlip.
5. Tap flange end of cylinder on wooden block to remove primary piston and spring, secondary piston and spring. it may prove necessary to feed compressed air into cylinder front delivery port.

NOTE: Once piston assemblies are withdrawn appropriate piston and spring must be kept together. In event of springs being mixed, the secondary piston spring can be easily identified, it being slightly thicker and longer than the primary spring.

Master Cylinder Pistons:

6. Remove spring, spring seat, recuperating seal and washer from secondary piston.
7. Carefully pry seals from rear of secondary piston.
8. Remove spring, spring seat, recuperating seal and washer from primary piston.
9. Carefully pry seal from rear of primary piston.
10. Discard all old seals and associated items that will be replaced by those contained within service kit.

INSPECTION
1. Clean all parts with Girling cleaning fluid and dry with lint-free cloth.
2. Examine piston and bore of cylinder for visible score marks and corrosion. If doubt exists as to condition of components replace suspect item.


WARNING: To help prevent damage it is essential that generous amounts of clean brake fluid are used at all stages of seal assembly.

REASSEMBLE
1. Carefully fit inner seal of secondary piston in locating groove. Be sure lip faces forwards.
2. Fit remaining seal in locating groove, be sure seal lip faces towards primary piston, i.e. in opposite direction of seal fitted in operation 1.
3. Fit washer, recuperating seal, spring seat and spring over forward end of secondary piston.
4. Carefully fit rear seal of primary piston in locating groove, be sure seal lip faces forward, i.e. away from circlip.
5. Fit washer, recuperating seal, spring seat and spring over forward end of primary piston.
6. Generously lubricate bore of master cylinder with clean brake fluid.

WARNING: Adherence to the following instruction is vitally important. Failure to comply will result in damaged piston seals.

7. Secure master cylinder in vice and generously lubricate piston seals in new brake fluid.
8. Position secondary piston assembly to cylinder until recuperating seal rests centrally in mouth of cylinder.

Fig. 5 Piston Assembly:

9. Ensuring seal is not trapped, slowly rotate and rock piston assembly while GENTLY introducing piston into cylinder bore.
10. Once recuperating seal enters bore of cylinder, SLOWLY push piston into bore in one continuous movement.
11. Repeat operations 9 and 10 with primary piston and spring.
12. Pressing piston into bore of cylinder, fit circlip.
13. Press primary piston into bore of cylinder to full extent, fit secondary piston stop pin.
14. Fit sealing grommets to master cylinder.
15. Lubricate hose adaptors with brake fluid and press into sealing grommets.

Fig. 6 Secondary Piston Stop Pin Assembly:

Fig. 7 Sealing Grommet Installation:

REFIT
7. Reverse steps 3 to 6 under REMOVE.
8. Bleed brakes.
9. Refit reservoir filter and sealing cap.
10. Connect leads to fluid level indicator and replace cover.