How to Adjust the Brake Master Cylinder Push Rod

The master cylinder and brake booster push rods form a mechanical link between the brake pedal and the master cylinder itself. On most vehicles, the actual master cylinder push rod is not adjustable. Instead, an adjustable push rod is used to link the brake pedal and the vacuum booster. This adjustable push rod is used to control both the height and free play of the brake pedal. Proper adjustment is critical to insuring the brakes do not drag and the brake pedal has a predictable response and feel when depressed. Adjusting the push rod is a relatively easy task vehicle owners can do themselves.

Instructions

1

Park the automobile. Move the driver's seat to the rearmost position to give yourself easy access to the brake pedal area. Open the vehicle hood, and locate the brake fluid reservoir. This is a transparent plastic container mounted near the rear of the engine compartment on the driver's side. Remove the reservoir cap.

2

Start the engine. Have an assistant depress the brake pedal slowly and gently with his hand while you look into the brake fluid reservoir. Note how far the brake pedal is depressed when you first see signs of a splash or turbulence in the brake fluid reservoir. This amount of brake pedal travel is known as free-play. Typically, the free-play should be about 1/4 to 3/8 of an inch. If the free-play is outside this range, you must adjust the push rod.

3

Slide under the dashboard, and look up toward the top of the brake pedal arm. You will see a threaded rod extending from the front wall of the passenger compartment attaching to the upper brake pedal arm. You will also see lock-nuts at one or both ends of the rod. Place a visible dot at about the mid-point of this rod with 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 to adjust the brake pedal free-play and height. With the lock-nuts loosened, you should be able to rotate the rod by hand. Rotating clockwise will increase free-play, while rotating counterclockwise will have the opposite effect. Use the dot you placed on the push rod as an indicator of how far you have moved the rod.

6

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. Tighten the lock-nuts with a wrench. Double-check the brake pedal free-play as above, and readjust if needed.

7

Check the operation of the brakes and the brake lights before driving.