How to Adjust Drum Brakes

by Jody L. Campbell

Drum brakes are used only on the rear of some vehicles. Today, many vehicles are being manufactured with four-wheel disc brakes. Vintage cars were made with four-wheel drum brakes, but the braking response was not as good as that of disc brakes. With that in mind, drum brakes only supply the vehicle with up to 25 percent braking capacity. That means the front disc brakes do most of the work. If the rear drum brakes become unadjusted (and there are a few common factors that account for that), the front ones begin to overcompensate. Problems in the front brakes can become apparent if they're overworked. Keeping the rear brakes adjusted is a safe and effective way to balance the braking system and increase the longevity of your front brakes.

Remove the hub caps from the rear wheels and break the lug nuts loose with the lug wrench.

Lift the rear of the vehicle with the floor jack and secure it onto the jack stands.

Remove the nuts and wheels.

Locate the adjusting porthole on the back of the backing plate. There should be a rubber plug capping the porthole to protect it from the elements. Remove the plug by prying it out with a screwdriver.

Insert the long screwdriver into the porthole and feel your way around for the adjusting retainer clip. If necessary, grab a flashlight and crawl under the vehicle to look for it. It's a small lever that holds the star wheel in position. Depress the clip with the screwdriver away from the star wheel and use the brake spoon adjuster (or another straight-edge screwdriver) to turn the star wheel in one direction.

Spin the drum by hand. If the tension is increasing, you're going the right way to adjust the brake shoes. If the tension is decreasing and the drum is spinning more freely, you're un-adjusting the shoes. Go back and use the spoon to turn the star wheel in the opposite direction.

Occasionally, between making adjustments, yank on the parking brake cable near the rear of the backing plate to center the shoes.

Continually check the tension of the shoes against the drum by spinning the drum (every four to five turns of the star wheel). The drum needs to move, but there should be a dragging sensation on the drum from the shoes contacting the inside diameter of the drum as you spin it. Adjust the brake shoes upward so the drum cannot complete a full revolution of spinning on its own (or half a revolution, if desired).

Repeat this procedure for the other side.

Carefully get into the vehicle and apply the brake pedal and parking brake mechanism simultaneously. This will center the shoes and integrate the parking brake mechanism.

Apply the parking brake and let it sit. Check both rear drums to make sure they're holding correctly. If one is holding and the other isn't, you need to locate the equalizer of the parking brake cable and adjust it. Refer to the repair manual for your specific vehicle for the correct procedure.

Readjust both sides after you have pumped the foot brake pedal while applying the parking brake mechanism, and adjusted the equalizer if applicable.

Replace the porthole plug when finished. Replace the wheels and lug nuts and tighten.

Tip

  • check Some vehicles are manufactured with portholes that have not been "punched" out of the backing plate. This will require removing the drum (to get the tab out once it's punched in). You can use a hammer and a punch to pound in the metal tab, but you should also get a rubber plug to cap it off. If you're unable to turn the star wheel, you will need to remove the rear drum and the star wheel adjuster mechanism. Often, this part can be serviced by taking it apart, cleaning it, applying lubricant to the threads and then replacing it. If you cannot service the star wheel adjuster, it will have to be replaced. Import vehicles use a self-adjusting cam action lever. There is no star wheel adjuster in these type of vehicles. The rear drum would need to be removed for you to inspect the cam adjuster to make sure it's working properly. On most of these vehicles, the rear brakes can be adjusted by activating the brake pedal and the parking brake mechanism repeatedly. You can also adjust the parking brake mechanism on these vehicles to tighten the internal ratchet of the handle. Refer to the repair manual for the location of this adjustment. Using the parking brake on most vehicles will increase the longevity of the rear drum brake adjustments. If you're not in the habit of using it, try to get into it. Do not drive off with the parking brake applied, however, as this will cause stress in the rear brakes, prematurely wear down the brake shoes, and put the engine and transmission under duress.

Items you will need

About the Author

Jody L. Campbell spent over 15 years as both a manager and an under-car specialist in the automotive repair industry. Prior to that, he managed two different restaurants for over 15 years. Campbell began his professional writing career in 2004 with the publication of his first book.