Removal & Installation
Make sure that the booster rubber reaction disc is properly installed if the master cylinder push rod is removed or accidentally pulled out. A dislodged disc may cause excessive pedal travel and extreme operation sensitivity. The disc is black compared to the silver colored valve plunger that will be exposed after the push rod and front seal is removed. The booster unit is serviced as an assembly and must be replaced if the reaction disc cannot be properly installed and aligned, or if it cannot be located within the unit itself.
- Disconnect the stop lamp switch wiring to prevent running the battery down.
- Support the master cylinder from the underside with a prop.
- Remove the master cylinder-to-booster retaining nuts.
- Loosen the clamp that secures the manifold vacuum hose to the booster check valve, and remove the hose. Remove the booster check valve.
- Pull the master cylinder off the booster and leave it supported by the prop, far enough away to allow removal of the booster assembly.
- From inside the cab on vehicles equipped with push rod mounted stop lamp switch, remove the retaining pin and slide the stop lamp switch, push rod, spacers and bushing off the brake pedal arm.
- From the engine compartment remove the bolts that attach the booster to the dash panel.
- Mount the booster assembly on the engine side of the dash panel by sliding the bracket mounting bolts and valve operating rod in through the holes in the dash panel.
Make certain that the booster push rod is positioned on the correct side of the master cylinder to install onto the push pin prior to tightening the booster assembly to the dash.
- From inside the cab, install the booster mounting bracket-to-dash panel retaining nuts.
- Position the master cylinder on the booster assembly, install the retaining nuts, and remove the prop from underneath the master cylinder.
- Install the booster check valve. Connect the manifold vacuum hose to the booster check valve and secure with the clamp.
- From inside the cab on vehicles equipped with push rod mounted stop lamp switch, install the bushing and position the switch on the end of the push rod. Then install the switch and rod on the pedal arm, along with spacers on each side, and secure with the retaining pin.
- Connect the stop lamp switch wiring.
- Start the engine and check brake operation.
System Operation Test
- With the engine OFF , pump the brake pedal until the supply vacuum is entirely gone.
- Put light, steady pressure on the brake pedal.
- Start the engine and let it idle. If the system is operating correctly, the brake pedal should fall toward the floor if the constant pressure is maintained.
Power brake systems may be tested for hydraulic leaks just as ordinary systems are tested.
Vacuum Leak Test
- Operate the engine at idle without touching the brake pedal for at least one minute.
- Turn off the engine and wait one minute.
- Test for the presence of assist vacuum by depressing the brake pedal and releasing it several times. If vacuum is present in the system, light application will produce less and less pedal travel. If there is no vacuum, air is leaking into the system.