Power Brake Unit: Disassembly

Remove pushrod boot, silencer, front housing seal, grommet and vacuum check valve.
Scribe a mark on front and rear housings for reassembly reference. Attach front housing to suitable holding fixture. (Cadillac J-23456, all others J-22805-01).
On Cadillac, press down on tool J-23456 and turn counterclockwise to unlock housings. On all others, place spanner J-9504 over rear housing studs, press down and turn counterclockwise to unlock housings.
Remove power piston group, power piston return spring, and power piston bearing. Remove piston rod, reaction retainer and power head silencer.
Grasp assembly at outside edge of divider and diaphragms. Hold with pushrod down against a hard surface. Use a slight force or impact to dislodge diaphragm retainer.
Remove primary diaphragm, primary support plate, secondary power piston bearing, housing divider, secondary support plate and diaphragm and power piston assembly.

Fig 1: Exploded View of Delco-Moraine Tandem Power Cylinder
Courtesy of GENERAL MOTORS COMPANY

Fig 2: Exploded View of Delco-Moraine Tandem Power Piston Group
Courtesy of GENERAL MOTORS COMPANY