The master cylinder pushrod runs from the master cylinder, through the brake vacuum booster, through the firewall, and attaches to the arm of the brake pedal. When the brake pedal is pushed, the pedal motion is transmitted to the master cylinder, where this mechanical motion is converted to hydraulic fluid power, which is in turn transmitted to the brakes. If the pushrod is not adjusted correctly, then either the brake pedal will have to be pushed down a long way before the brakes start to engage, or the brakes will always be dragging and may suddenly grab with the driver's slightest touch on the pedal.
Park the vehicle, and push the driver's seat back as far as it will go.
Gently push the brake pedal a few times with your hand. Note how far the pedal will move before the pushrod starts to move. You should feel the pedal go down about one-fourth to one-half of an inch before you feel the bump of the pushrod engaging and a slightly increased resistance as the pedal moves down further. This distance is known as the brake pedal freeplay. If it is greater than the distance stated above, then it is too much, and if it is less or nonexistent, then it is too little.
Slide your body under the dashboard, and look up toward the top of the brake pedal arm. A flashlight or work light is handy here. Locate the threaded pushrod that comes out of a rubber boot or metal housing on the front wall of the car and attaches to the back of the brake pedal arm near the top. There is a locknut on the pushrod at the brake pedal end, and often another locknut at the end near the front wall as well. Use a marker to make a visible mark on the pushrod roughly at the middle of the visible portion of the pushrod. You will be using this mark to judge the rotation of the pushrod, so be sure you can see it well.
Loosen the locknuts at both ends of the pushrod. Grip the pushrod firmly with pliers to prevent it from rotating while you are loosening the lock nuts. If the pushrod does rotate a little, return it to its original position using the mark as a reference.
Rotate the pushrod clockwise to increase pedal height and pedal freeplay, and counterclockwise to reduce pedal height and freeplay. The pushrod can be rotated by hand or with pliers if necessary. Be careful when reducing the freeplay, as the mechanism will reach a point where the pedal is no longer being lowered, but the pushrod is being pulled out instead. This is effectively moving the master cylinder piston from its normal rest position, and brake drag will result. You can tell how far you have adjusted the pushrod by checking the relative position of the mark that you placed on it.
Adjust the pushrod until the pedal freeplay is in the range of one-fourth to one-half of an inch. Carefully tighten the locknuts, taking care not to rotate the pushrod while doing so. Test the brake operation before driving normally.
