Master Cylinder Push Rod

Place Booster Piston Rod Gauge (J-39567) on master cylinder with master cylinder gasket in place. Lower booster piston rod gauge pin until its tip just touches end of master cylinder primary piston. See Fig 1 .
Remove booster piston rod gauge, turn it upside down, and place it on front of brake booster assembly. See Fig 2 . On 2-door without ABS brakes, clearance between master cylinder primary piston and booster piston rod should be .01-.02" (.25-.50 mm). On all other models, clearance should be .006-.014" (.14-.35 mm).
If clearance is present, adjust booster piston rod length by turning adjustment nut at end of piston rod until rod just touches master cylinder primary piston.

Fig 1: Adjusting Push Rod (Gauge Shown On Master Cylinder)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Adjusting Push Rod (Gauge Shown On Brake Booster)

Courtesy of GENERAL MOTORS CORP.