Auto Repair: Checking Drum Brakes
As you can see in Figure 15-3, you have to remove a bunch of stuff to get to a drum brake. The steps here explain how to do so and what to look for when you finally get to your brakes.
Caution: Arrange to do this work in a wellventilated area, wear an inexpensive but protective paper mask, and be very careful not to inhale the dust from the brake drum. If you have an older vehicle, it probably contains asbestos. If you get asbestos in your lungs, you run the risk of serious lung disease. Even asbestos-free brake dust is nasty stuff when inhaled.
Follow these steps to check drum brakes:
- Jack up your vehicle.
Be sure to observe safety precautions with that jack!
Car smarts: 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.
- If you have a hubbed drum, pry the grease cap off the end of the hub using a pair of combination slip-joint pliers and lay the grease cap on a clean, lint-free rag.
Tip: 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.
- Look at the cotter pin that sticks out of the side of the castellated nut or nut-lock-and-nut combination.
Notice in which direction it's placed, how its legs are bent, how it fits through the nut, and how tight it is. If necessary, make a sketch.
- Use a pair of needle-nosed pliers to straighten the cotter pin and pull it out.
Put it on the rag that you're using to hold all the parts you've taken off, and lay it down pointing in the same direction as when it was in place.
- 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.
- 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.
- Carefully slide the outer bearing, with the washer in front of it, off the spindle.
- Tip: Whether or not you want to repack your wheel bearings, check them now. Then resume with Step 9.
As long as you're removing your bearings, you should check them for wear. If they're packable, it's a good idea to repack them while you have everything apart. (All this task involves is squishing wheel-bearing grease into them, a wonderfully sensual job.)
- Carefully slide the drum off the spindle, with the inner bearings inside it.
Caution: Inhaling brake dust can make you seriously ill. For safety's sake, never attempt to 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.
- 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 (see Figure 15-4). If the drums aren't worn past legal tolerances (0.060 of an inch), they can be reground (or turned) rather than replaced. A special machine called a brake-lathe does this job in a relatively short amount of time. It shouldn't be a major job in terms of expense. You could do it yourself, under supervision at a school auto shop; most classes have the machine.
Caution: If you need new drums, have a professional install them for you because the brake shoes must be adjusted to fit. Make sure that the shop orders drums for your exact make, model, and year and that they specify drums for front or rear wheels. Brake drums must also be replaced with drums of the same size for even braking performance. The new drums should look exactly the same as your old ones.
- Look at the rest of your brakes, which are still attached to the brakebacking plate (see Figure 15-5).
Here are the parts you should look at, what you should find, and what to do if they need to be repaired or replaced:
- Wheel cylinders: The wheel cylinders should show no signs of leaking brake fluid. If they're leaky, consult a brake shop.
- 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.
Tip: If your brake drums have been wearing evenly and your vehicle has been braking properly, disregard the grooves and the glazing unless your linings look badly worn. If your linings are worn, have them replaced at once. This job involves replacing the brake shoes with new ones that have new linings on them. For even performance, always replace brake shoes in sets (four shoes for two front or rear wheels is a set). Replacing them all at once is even better.
- Take a look at the self-adjusting devices on your brakes. (Figure 15-5 shows one of the most common self-adjusters.) 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.
Is the cable hooked up? Does it feel tight? 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. If this approach doesn't work, you may need a professional to adjust them. Don't attempt tofiddle with these parts yourself.
From Auto Repair for Dummies, copyright © 2009 by Wiley Publishing, Inc., Indianapolis, Indiana. Used by arrangement with John Wiley & Sons, Inc.