How to Check Disc and Drum Brakes

You should check disc brakes and disc brake linings every 10,000 miles — more often if your brakes suddenly start to squeal or pull to one side, or if your brake pedal flutters when you step on it. Don’t confuse the fluttering with the normal pulsing of ABS brakes when they’re applied in an emergency stop.

Today, most vehicles have four-wheel disc brakes. Others have disc brakes on the front wheels and drum brakes on the rear wheels.

When you check your disc brakes, measure the thickness of the linings on the pads so that you can tell whether the linings on your brakes are badly worn. If the lining is down to the thickness of the steel backing plate, the pads should be replaced.

1. Jack up your vehicle and remove a front wheel.

   Use wheel blocks for safety.

2. Look at the brake disc (also called a rotor), but don’t attempt to remove it from the vehicle.

   

   Check your disc brakes.

   The brake caliper has to be removed before you can remove a brake disc, and the good news is that there’s no need to do so. If you’re working alone, just check the visible part of the disc for heavy rust, scoring, and uneven wear. Rust generally is harmless unless the vehicle has been standing idle for a long time and the rust has really built up.

   If your disc is badly scored or worn unevenly, have a professional determine whether it can be reground or needs to be replaced.

3. Inspect your brake caliper (the component blocking your view of the entire brake disc).

   Be careful. If the vehicle has been driven recently, the caliper will be hot. If it’s cool to the touch, grasp it and gently shake it to make sure that it isn’t loosely mounted and its mounting hardware isn’t worn.

4. Peek through the inspection hole in the dust shield on the caliper and look at the brake pads inside.

   If the linings on the brake pads look much thinner than the new ones you saw at the supply store or dealership parts department, they probably have to be replaced. If the linings have worn to the metal pads, the disc probably has to be reground or replaced as well.

5. Replace your wheel, lug nuts, and hubcap, and lower the vehicle to the ground.

   If the disc and pads seem to be in good condition and your brake pedal doesn’t flutter when you step on it, you don’t need to do anything else.

Relining, caliper maintenance, and disc grinding should be left to a professional unless you do the job under supervision at an auto class.

How to Check Drum Brakes

You have to remove a bunch of parts 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 the steps below 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.

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

   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

    • 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 one-sixteenth of an 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.