Power Brake Units - DELCO-Moraine Tandem Diaphragm: Overhaul: Reassembly
- Replace vacuum check valve, with new grommet. Install front housing seal. Place new "O" ring on air valve. Insert air valve end of air valve-push rod assembly into primary power piston tube.NOTE: If floating control valve requires replacement, complete air valve-push rod assembly must be replaced.
Seat floating control valve retainer on valve assembly. Manually press assembly so that floating control valve bottoms on tube. Suitable installer tool (J-23175) may be used. Install air filter and retaining ring in primary power piston tube. Position rubber reaction bumper on end of air valve.
- If replacing either power piston with new parts, the following procedure should be used: Hand tighten power pistons to each other, without air valve spring (air valve-push rod assembly should be already assembled, as previously described). Insert and seat reaction piston into secondary power piston. Place suitable gauge (J-23337) in secondary power piston, with outer edge of gauge resting on bottom of large cavity (center section on gauge in smaller cavity). Move gauge to right or left of end of reaction piston. Piston is correct length if end of piston hits, but does not unseat, gauge. Replace with proper service piston if length is incorrect (too short or too long).
- Place rubber reaction disc in large cavity of secondary power piston and seat disc on reaction piston. Unlock power pistons. Assemble primary diaphragm to primary support plate. Press raised flange of diaphragm I.D. through center hole of support plate (ensure plate fits in flange groove).
- Mount power piston tool (J-23101) in vise, with small diameter end up. Position primary power piston on tangs of tool. Holding edge of primary support plate, place on power piston, press down, and rotate clockwise until assembly locks. Place power head silencer on tube of primary power piston, covering holes at base of tube.
- Assemble secondary power piston, diaphragm, and support plate in same manner as primary power piston assembly (turn tool over, with large diameter end up).
- Apply talcum powder to bead on O.D. of secondary diaphragm. Hold housing divider with primary diaphragm holding flange facing down. Install secondary bearing in I.D. of divider, with extended lip of bearing upward. Install suitable bearing protector tool (J-23188) on threaded end of secondary power piston. Hold housing divider with six oblong protrusions upward. Press divider down over tool and onto secondary piston tube (against diaphragm support ring). Remove bearing protector tool, but do not remove power piston tool.
- Fold diaphragm away from O.D. of primary support plate. Position small end of air valve return spring on air valve. Set primary power piston on tubular portion of secondary power piston (ensure air valve return spring seats properly). Press down and screw power pistons tightly together. Pull diaphragm O.D. over flange of housing divider. Insert master cylinder piston rod into secondary power piston until flat end bottoms against rubber reaction disc.
- Install new rear housing seal. Mount front housing on suitable holding fixture (J-22805). Assemble power piston group to rear housing. Press down until housing divider seats in rear housing and primary power piston bottoms against housing. Place piston rod retainer plate on end of power piston return spring in front housing.
- Place housings in position to be locked (note location of scribe marks). Check to be sure piston rod retainer goes through center of retainer plate. Lock housings in reverse manner of separation, using appropriate tools.
- Place silencer in closed end of power head boot. Stretch boot over push rod and over flange in center of rear housing. Install boot retainer. Install push rod clevis and lock nut, if equipped.