GM 91174788
Brake Booster

First step when replacing the vacuum Brake Booster (Non-ABS) is to detach the master cylinder assembly. Unclip the brake vacuum hose from the booster and undo the clevis pin from the push rod clevis before taking off the push rod clevis and brake pedal arm. Unscrew the booster nuts then withdraw the booster from its position. To get the correct position of the reaction disc push the piston rod several times before measuring the clearance with the booster at its atmospheric pressure. Place the j39567 Brake Booster piston rod height gauge (J39567) on top of the master cylinder to push down the pin which should reach the piston. Then turn the gauge upside down and put it on the booster assembly . The booster piston rod should sit at zero millimeters directly against j39567. Check the piston rod distance between the booster surface where it measures between 9.40 and 9.62 millimeters or 0.370 and 0.378 inches. When measurements fall out of specification you should apply the j44485 booster push rod adjuster wrench to grip the booster piston rod while adjusting the clearance by turning its screw. Before connecting the bulkhead nuts apply wheel bearing lubricant (GM P/N 1051344) on the master cylinder piston and position the booster properly without tightening the bulkhead nuts yet. Fasten the four booster nuts into place afterward position and secure the booster push rod clevis to the brake lever by inserting the clevis pin and clip. Position the push rod clevis carefully until the measurement between its pin hole and Brake Booster is within 109.5 to 110.5 millimeters (4.31 to 4.35 inches). Twist the clevis nut to 19 nm (14.0 ft. Lbs.) and the booster nuts to 13 nm (115.0 inch lbs). End the process by attaching the brake vacuum hose to the Brake Booster and using the hose clamp to secure it afterward you install the master cylinder.

Disconnect the brake vacuum hose from the brake booster.

Remove the Brake Pressure Modulator Valve from the vehicle.

Place the J 39567 on the master cylinder and push the pin down until it touches the master cylinder piston. Remove the J 39567, turn it upside down, and set it on the booster assembly; the clearance should be 0 mm (0 inch).