Brake Booster Trouble Shooting

Corvette Power Brake Booster Basic Diagnostic Test

1. With the engine off depress and release the brake pedal several times to bleed vacuum from the power section.

2. While holding the the pedal down with approximately 15 to 25 pounds of pressure, start the engine.

3. If the power booster is operating the pedal will fall slightly and require less pressure to hold it down.

IF BOOSTER IS NOT OPERATING & THERE IS A VERY HARD PEDAL

Disconnect the vacuum hose from the booster check valve and with a vacuum gauge measure the vacuum level at this point while the engine is running. You should have at least 18" vacuum to the booster. Anything less will begin to give a hard pedal. lf the vacuum level is below 18", check the vacuum system for leaks. If none are present, you may be able to tune the engine and bring the vacuum level up to at least 18".

If the vacuum level at the check valve is 18" check that the booster check valve is working. Disconnect the vacuum hose at the check valve and attach a piece of tubing. Blow into the valve. If air passes through the valve it is defective and must be replaced. Also look into the hose attachment neck on the check valve and be sure there is no obstruction inside the valve.

Check your booster for a vacuum leak. With everything hooked up run the engine at moderate speed. Release the accelerator and turn the engine off. Wait 90 seconds and apply the brakes. If the brake applications are power assisted there is no leak. If there is no power assist the booster is defective and must be replaced.

IF THE BOOSTER IS OPERATING BUT YOU STILL HAVE A HARD PEDAL

You may have frozen caliper pistons which can cause a very hard pedal.

IF YOUR BRAKE PEDAL IS VERY SENSITIVE AND THE BRAKES GRAB

The booster has a crack in the phenolic hub inside the booster which will mean it will be either totally on or totally off. Any slight pressure to the pedal will cause the brakes to lock up. The booster must be replaced.