Vacuum Brake Booster: Service and Repair

Fig. 15 Support fixture installation. Chevrolet Nova:

Fig. 16 Toyota/GM brake booster exploded view:

Disassembly
1. Attach holding fixture J-22805-01 or equivalent to front of booster, then mount fixture in vise, Fig. 15. Mounting holes of holding fixture may have to be elongated toward inside in order to accommodate booster master cylinder studs.
2. Scribe matching marks between front and rear booster shells to aid assembly.
3. Remove nut from pedal pushrod and boot from rear shell, Fig. 16.
4. Attach lever J-9504-01 or equivalent to booster mounting studs, Fig. 15, rotate rear shell counterclockwise to unlock housing, then separate booster shells and remove holding fixtures. Care must be taken not to release spring tension suddenly when separating booster shells.
5. Remove diaphragm spring and pushrod from front shell.
6. Remove diaphragm and piston assembly from rear shell.
7. Support rear shell inboard of mounting studs, then drive our rear seal using suitable spacer.
8. Rotate valve body clockwise, and separate valve body and diaphragm from booster piston.
9. Push pedal pushrod into valve body, supporting valve body on cushioned work surface, then remove stopper key from side of valve body.
10. Pull pushrod from valve body, then remove 2 felt and 1 sponge element, noting position for assembly.
11. Remove reaction disc from front of valve body.
12. Pry out retaining ring, then remove seal from front shell.

Fig. 16 Toyota/GM brake booster exploded view:

Fig. 17 Brake booster lubrication points. Chevrolet Nova:

Assembly
Apply suitable silicone grease to components indicated in Fig. 17 prior to assembly.
1. Install new seal in front shell and secure with new retaining ring.
2. Install holding fixture J-22805-01 or equivalent on front shell, then mount holding fixture in vise.
3. Support front of valve body on cushioned work surface, press pedal pushrod into valve body, then secure pushrod by inserting stopper key into side of valve body.
4. Pull up on pushrod to ensure that key is properly seated, then install elements (2 felt and 1 sponge) in rear of valve body and reaction disc in front of valve body, Fig. 16.
5. Mount diaphragm on booster piston.
6. Insert valve body assembly into booster piston and rotate valve body counterclockwise to lock in position.
7. Support rear shell from inside, inboard of mounting studs, and drive new rear seal into place using suitable spacer.
8. Install diaphragm assembly into rear shell, and the pushrod and return spring into front shell.
9. Position rear shell and diaphragm assembly over front shell and reinstall rotating lever J-9504-01 or equivalent, ensuring that matching marks will be aligned when assembly is rotated to locked position.
10. Apply vacuum to inlet port in front shell and rotate rear housing clockwise to locked position. If rear shell is too tight to be rotated when pressed into position, apply more silicone grease to lip of diaphragm contacting front shell.
11. Remove rotating lever and holding fixture, then install rear boot and pedal pushrod nut.
12. Adjust pushrod as outlined.