How to Troubleshoot a Power Booster

The power booster is a vital component of modern automotive braking systems. The booster harnesses a portion of the vacuum generated in the engine's intake manifold to triple or quadruple the force of the driver's push on the brake pedal, thus greatly reducing the effort needed in braking. Unfortunately, this also means that any problem with the power booster can result in a huge effort being needed to slow or stop the vehicle, potentially creating a dangerous situation. Fortunately, testing the power booster operation is a relatively simple procedure that any driver can perform themselves.

Instructions

1

Park the vehicle and let the engine idle for about a minute. Hold the brake pedal down with a light and steady force and turn the engine off. Continue to hold the brake pedal down for a minute or so and pay close attention to any changes in the pedal position. The pedal should remain in the same position. If the pedal slowly rises it means that the power booster is not air-tight and is losing vacuum.

2

Pump the brake pedal a few times to use up any vacuum left in the booster with the engine still off. Hold the brake pedal down with a light and steady force and then start the engine. Pay close attention to changes in the pedal position. The brake pedal should drop about a quarter of an inch when the engine starts, indicating that the power booster is functioning properly.

3

Allow the engine to run at idle for about a minute. Shut the engine off and immediately pump the brake pedal five or six times, waiting about five seconds between each pump. Pay close attention to the position at which the brake pedal stops. If the booster is functioning properly, the pedal will stop at a slightly higher position with each pump. If the pedal stops at a low position with the first pump and then stops at the same high position on the following pumps it means the booster is not air-tight and is loosing vacuum.

4

Open the hood and locate the power booster. It is a dome-shaped device mounted to the firewall on the rear driver's side of the engine compartment. Locate the flexible vacuum line coming in to the booster. Trace the hose back to the engine intake manifold. Use pliers or a screwdriver to remove any retaining clips and then pull the vacuum line off of the intake manifold connection point.

5

Push the baster into the end of the vacuum hose and hold it firmly to get a good seal. Squeeze the baster bulb to force air into the power booster. If the booster check valve is working properly, you will not be able to force any air into the booster.

6

Release the pressure on the baster so that it is unsealed and squeeze and hold the bulb. Reseal the baster on the vacuum hose and release the bulb to suck air out of the booster. If the check valve is working properly, you should be able to easily suck a small amount of air out of the booster.

7

Connect an engine vacuum test gauge to the intake manifold vacuum connection and start the car. The gauge should show a reading of at least 18 inches of vacuum. If it does not, your vehicle may need a tune-up.