Power Brake Units - DELCO-Moraine Single Diaphragm: Overhaul: Disassembly

Scribe a mark on bottom of front and rear housings for reassembly. Attach a suitable holding fixture (J-22805) to front of housing. Make sure holding fixture is bolted down tight against housing to prevent damage to studs.
Clamp base of holding fixture in a vise. Make sure power section is up. If the unit has a straight mounting bracket, attach a suitable spanner wrench (J-9504) to studs on rear of housing. Make sure nuts are tight to avoid damaging studs.
If the unit has a tilt mounting bracket, place a suitable adapter (J-22893) inside tilt bracket. Place spanner wrench on adapter and tighten nuts on studs.
On all type units, press down on spanner wrench and rotate rear housing counterclockwise to unlocked position. Care must be taken as housing is loosened as it is spring loaded. Remove tools.
Remove rear housing and power piston assembly from unit. Remove return spring. Remove retaining ring on push rod then remove silencer. Remove seal, vacuum check valve and grommet from front housing.
NOTE: Care must be taken during the following procedures to prevent damage to diaphragm.
Remove power piston assembly from rear housing. Remove silencer from neck of power piston tube. Remove power piston lock ring by prying out one end from under large divided locking lug. Now pull ring from 2 locking lugs on power piston.
Remove reaction retainer, piston, reaction plate, 3 reaction levers and air valve spring. Remove reaction bumper and air valve spring retainer from air valve.
Place the square shank of a suitable power piston wrench (J-21524) in a vise. Pull diaphragm edges away from support plate so that hands grip steel support plate. Now place assembly on wrench in vise so that 3 lugs on tool fit 3 notches in power piston.
Press down on support plate and rotate counterclockwise until support plate separates from power piston. Remove diaphragm from support plate and lay to side.
Drill a 1 3/8" hole in the center of a 2" x 4" x 8" wood block. Place power piston with tube down in wood block. Place block in a vise and clamp in place. Make sure tube is not clamped.
Remove snap ring on air valve. Place power piston, tube down in a press. Using a 3/8" drive extension, press out air valve assembly. Now remove floating control valve, floating valve retainer, push rod limiter washer and air filter.
Remove floating control valve assembly from push rod. Discard control valve as a new one must be installed. Remove master cylinder push rod then remove "O" ring from push rod.