How to Adjust the Pedal Height on a Power Brake Booster

Today nearly all automobiles are equipped with power-assisted braking systems. These provide the driver with a very predictable and consistent response, which gives the driver better control of the braking process. This consistent feedback to the driver depends on the proper adjustment of the various braking components, including the height and free play of the brake pedal. Adjusting the brake pedal height is not difficult, and it saves you a trip to your local mechanic.

Instructions

1

Park the vehicle and move the driver's seat as far back as possible to give yourself good access to the brake pedal. Measure the vertical distance from the floor under the brake pedal to the center of the pedal. Compare the measured height to the manufacturer's specification as found in the vehicle's shop manual or an aftermarket equivalent repair manual such as Hayne's or Chilton. These are often available at your local public library.

2

Start the car and gently push the brake pedal with your hand while carefully feeling the resistance. The pedal should go down about 1/4 to 3/8 inch, at which point you should feel a light bump and the pedal resistance should increase slightly. This bump occurs when the master cylinder starts to engage, and the distance that the brake pedal travels to reach this point is known as free play. Compare the amount of free play to the manufacturer's specification as found in the vehicle's shop manual or an aftermarket equivalent repair manual.

3

Slide under the dashboard and look up to where the brake pedal is mounted. You will see a threaded push rod protruding from the front wall of the passenger compartment. The end of the push rod connects to the upper part of the brake pedal arm. You will also see lock-nuts at one or both ends of the rod. Mark a dot at roughly the mid-point of the push rod using a marker.

4

Wrap a small rag around the push rod to protect the threads, and then grip the rod firmly with pliers to prevent it from rotating. Loosen the lock-nuts with a wrench.

5

Rotate the push rod clockwise to increase pedal height and pedal free play, and counterclockwise to reduce them. The push rod can be rotated by hand, or with pliers if necessary. Be careful when reducing the free play, as the mechanism will reach a point where the pedal is no longer being lowered but the push rod is being pulled out instead. This is moving the master cylinder piston from its rest position, and brake drag will result. You can gauge how far you have adjusted the push rod by checking the position of the dot that you placed on it.

6

Tighten the lock-nuts once the pedal height and free play are within the specified ranges. Be sure to grip the push rod firmly with pliers to prevent it from rotating when the lock-nuts are tightened.

7

Examine the brake pedal arm if you cannot bring both the free-play and the pedal height into line with the manufacturer's specifications. On some vehicles you will see holes through the arm above and below the push rod connecting point. Follow the adjusting procedure above to bring the freeplay into the specified range, forgetting about the pedal height, and then tighten the lock-nuts. Disconnect the push rod from the brake pedal arm by first removing the push rod clevis pin retaining clip and then slipping the clevis pin out of the mounting hole in the brake pedal arm. Move the push rod to a higher hole to raise the bake pedal or a lower hole to lower it. Insert the clevis pin through the holes in the push rod clevis and the brake pedal arm and secure in place with the retaining clip.

8

Test the operation of the brakes and the brake lights before driving. Take the time to become familiar with the changed feel of the brakes after adjustment