Vacuum Brake Booster: Service and Repair

Fig. 12 Girlock Brake Booster Exploded View:

Disassembly
1. Remove vacuum check valve from front housing.
2. Loosen tie rod nuts several turns (approximately 1/2 inch), but do not remove nuts.
3. Pry housing shells apart using a thin blade screw driver, taking care not to chip or mar housing shells, or cut diaphragm.
4. Clamp housing shells together with suitable holding fixtures, then remove tie rod nuts and spring washers. Failure to secure housing shells prior to removing tie rod nuts may allow housing shells to separate due to spring tension, causing damage and/or personal injury.
5. Slowly loosen clamp securing housing shells, then separate front shell and remove return spring, grommet and front seal from housing.
6. Remove pedal pushrod boot, gasket and tie rods from rear shell, Fig. 12.
7. Separate diaphragm bead from rear shell, tie rod boots from posts on shell, then remove vacuum piston assembly.
8. Remove diaphragm and tie rod boots from piston.
9. Remove rear seal from shell and washers from tie rod posts.
10. Remove output rod, retainer and reaction disc.
11. Remove stop plate from vacuum piston, pressing on open end while pulling on closed end of plate.
12. Remove valve assembly from vacuum piston. Do not disassemble valve assembly. If service is required, entire valve assembly must be replaced.

Assembly
Lubricate components where indicated with silicone grease.
1. Lubricate outer surface of valve assembly, then insert valve into vacuum piston and secure valve with stop plate, Fig. 12. Ensure plate is in fully locked position.
2. Lubricate reaction disc, then install disc in vacuum piston.
3. Install new tie rod boots in openings in vacuum piston, then liberally coat insides of boots with silicone grease.
4. Lubricate outer lip of diaphragm, then fit diaphragm into vacuum piston.
5. Press rear seal into shell, lubricate inner diameter of seal, then install washers over tie rod posts on rear shell.
6. Mount vacuum piston assembly in rear shell, pushing tie rod boots over posts. Ensure diaphragm bead is properly located around perimeter of shell.
7. Install tie rods through bores in rear shell.
8. Mount rear shell assembly in fixture J-23456-51A or equivalent, lubricate output rod, then install rod and new retainer in vacuum piston. Do not alter adjustment of convex screw on output rod. Rod length is determined during manufacturing and should not be disturbed.
9. Seat new front seal in front shell with metal face of seal toward outside.
10. Position return spring in vacuum piston, then install front housing. Ensure diaphragm bead remains properly positioned.
11. Press shell halves together by hand, then install spring washers and new retaining nuts on tie rods. Ensure concave side of washers face shell. Use only new replacement nuts furnished with repair kit when assembling booster shells.
12. Tighten nuts evenly until shells are .20 inch apart, then ensure diaphragm bead is still properly positioned.

Fig. 13 Measuring Booster Shell Assembly. Girlock Booster:

13. Continue tightening nuts evenly, approximately 1/2 turn at a time. Gauge housing assembly with tool J-35498, or equivalent as shown in Fig. 13.
14. Housing shells are properly assembled when distance between face of washer (3) and face of nut (4) is 3.87-4.86 inches, Fig. 13.
15. Reverse steps 1 and 2 of disassembly procedure to complete assembly.