How to Check Drum Brakes

3 of 8 in Series: The Essentials of Checking and Maintaining Your Vehicle's Brakes

You have to remove a bunch of stuff to get to a drum brake. The steps here explain how to check drum brakes and what to look for when you finally get to them. Follow these steps to check drum brakes:

Arrange to do this work in a well-ventilated area, wear an inexpensive but protective paper mask, and be very careful not to inhale the dust from the brake drum.

  1. Jack up your vehicle and remove a wheel.

    Brake drums are classified as either hubbed or floating (hubless). Hubbed drums have wheel bearings inside them; floating drums simply slide over the lug nut studs that hold the wheels on the vehicle.

    The outer workings of a drum brake.
    The outer workings of a drum brake.
  2. If you have a hubbed drum, pry the grease cap off the end of the hub using a pair of combination slip-joint pliers.

    If you have a floating drum, skip Steps 3 through 7 and just slide the drum off the hub.

    You sometimes need to strike floating drums with a hammer to break them loose from the hub.

  3. Look at the cotter pin.

    The cotter pin sticks out of the side of the castellated nut or nut-lock-and-nut combination.

    Notice its direction, how its legs are bent, how it fits through the nut, and how tight it is. If necessary, make a sketch.

  4. Straighten the cotter pin and pull it out.

    Use needle-nose pliers. Lay it down on a clean rag, pointing in the same direction as when it was in place.

  5. Slide the castellated nut or nut-lock-and-nut combination off the spindle.

    If it’s greasy, wipe it off with a lint-free rag and lay it on the rag next to the cotter pin.

  6. Grab the brake drum and pull it toward you, but don’t slide the drum off the spindle yet; just push the drum back into place.

    The things that are left on the spindle are the outer wheel bearings and washer.

  7. Carefully slide the outer bearing, with the washer in front of it, off the spindle.

    As long as you’re removing your bearings, you should check them for wear.

  8. Carefully slide the drum off the spindle, with the inner bearings inside it.

    Inhaling brake dust can make you seriously ill. Never blow away the dust with compressed air. Instead, put your mask on and saturate the dust completely by spraying the drum with brake parts cleaner according to the instructions on the can. Wipe the drum clean with a rag; then place the rag in a plastic bag and dispose of it immediately.

  9. Take a look at the inside of the drum.

    You can probably see grooves on the inner walls from wear. If these grooves look unusually deep, or if you see hard spots or burned places, ask your service facility to let you watch while they check out the drums with a micrometer.

    Checking drum wear with a micrometer.
    Checking drum wear with a micrometer.

    If the drums aren’t worn past legal tolerances (0.060 of an inch), they can be reground (or turned) rather than replaced.

    If you need new drums, have a professional install them for you because the brake shoes must be adjusted to fit.

  10. Look at the rest of your brakes, which are still attached to the brake backing plate.

    Here are the parts you should look at:

    The inner workings of a drum brake.
    The inner workings of a drum brake.
    • Wheel cylinders: These should show no signs of leaking brake fluid.

    • Brake shoes and linings: These should be evenly worn, with no bald spots or thin places. The brake lining should be at least 1/16-inch from the steel part of the brake shoe or 1/16-inch from any rivet on brake shoes with rivets, preferably more. The linings should be firmly bonded or riveted to the brake shoes. Most brake shoes and linings are built to last for 20,000 to 40,000 miles; some last even longer. If yours have been on your vehicle for some time, they’ll have grooves in them and may be somewhat glazed.

  11. Examine the self-adjusting devices on your brakes.

    Trace the cable from the anchor pin above the wheel cylinder, around the side of the backing plate, to the adjuster at the bottom of the plate.

    If your brake pedal activates your brakes before it gets halfway down to the floor, the adjustment is probably just fine. If not, and if the cylinders, linings, shoes, and so on are okay, the adjusting devices may be out of whack. Making a couple of forward and reverse stops should fix them.

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The Essentials of Checking and Maintaining Your Vehicle's Brakes

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