Vacuum Brake Booster: Service and Repair
Disassembly1. Remove pedal pushrod boot and silencer, check valve, vacuum switch and grommets, as equipped, and the front housing seal.
Fig. 7 Typical brake booster holding & support fixture installation. Delco-Moraine units:
2. Scribe matching marks between front and rear housing sections, then mount booster assembly in suitable holding fixture with rear housing facing up.
3. Apply pressure to housing with holding fixture forcing screw and rotate rear housing counterclockwise to unlock housing halves.
4. Slowly release spring tension, then remove booster assembly from holding fixture.
WARNING: Do not allow spring tension to release suddenly, as damage or personal injury may result.
5. Lift off rear housing, then remove primary power piston bearing from housing.
Fig. 8 Delco-Moraine tandem diaphragm booster exploded view:
6. Remove power piston group and return spring from front housing.
Fig. 9 Power head assembly exploded view. Delco-Moraine tandem diaphragm booster:
7. Remove master cylinder piston rod and reaction retainer from front of piston, then the silencer from the rear of the assembly.
8. Hold piston assembly at edges of divider and strike pedal pushrod against work surface to dislodge diaphragm retainer.
Fig. 10 Girlock brake booster exploded view:
9. Remove primary diaphragm and support plate, secondary power piston bearing and housing divider, and the secondary diaphragm and support plate from piston, noting installation position of components.
10. Clean and inspect components as outlined in General Service and replace as needed.
NOTE: Do not disassemble power piston. If service is required, power piston is replaced as an assembly.
Assembly
1. Position power piston assembly on work surface with pedal pushrod facing up.
2. Lubricate inner lip of secondary diaphragm, fit diaphragm over support plate, then install assembly onto power piston.
Fig. 9 Power head assembly exploded view. Delco-Moraine tandem diaphragm booster:
3. Install secondary power piston bearing into divider with flat surface of bearing on side of divider with 6 lugs.
4. Install guide sleeve J-28458 or equivalent over power piston, lubricate inner diameter of secondary bearing, then install divider assembly with lugged side facing up.
5. Lubricate inner lip of primary diaphragm. Fit diaphragm over support plate, then install diaphragm assembly on power piston.
6. Ensure that diaphragms and support plates are properly positioned, install new diaphragm retainer, then seat retainer on power piston using guide sleeve J-28458 or equivalent and suitable hammer.
7. Install primary power piston bearing in rear housing and lubricate inner diameter of bearing.
Fig. 8 Delco-Moraine tandem diaphragm booster exploded view:
8. Mount front housing in holding fixture J-23456 or equivalent, then install diaphragm return spring, power piston group and the rear housing assembly.
9. Ensure that housing matching marks are properly aligned, then press housing sections together with holding fixture forcing screw.
NOTE: Housing assembly can be facilitated by applying vacuum to front housing port, blocking opening for vacuum switch, if equipped.
10. Rotate rear housing clockwise to lock housing, then stake 2 tabs 180° apart to secure assembly. Do not restake tabs that have been used previously.
11. Lubricate grommets and front seal, then install grommets, check valve and vacuum switch, as equipped, and the front housing seal.
12. Install silencer and pedal pushrod boot.