Brake System Repairs

Brakes are an obviously important part of your car. Although many car owners leave brake work to a specialist, it doesn’t have to be so. Brake parts are commodities, easily found at larger auto parts stores. The steps to repairing or replacing brake parts are easy to follow. The job requires few special tools beyond those in your car care toolbox. Can you do the job as well as a brake specialist? Maybe not. But you can do it adequately-and sometimes better than a poorly trained employee who last week was grilling hamburgers. Specialists know more; you know less. They have a hundred brake jobs to do this week; you have just one. Most cars today use a hydraulic brake system (see the figure showing a brake system) with drum brakes on the rear, disc brakes on the front, and each with a brake cylinder that’s controlled by the master cylinder. A hydraulic system uses brake fluid to force the brakes against moving parts in the wheels. Some cars have a proportioning valve that keeps the rear brakes from locking up when you slam on the pedal. Antilock brake systems (ABS) have a built-in proportioning valve and some electronics to control skidding. Like more and more systems on today’s cars, the ABS is controlled by an electronic computer. Each brand is just a bit different to service. If your car has an ABS, find and follow the service manual. ABS systems usually can tell you what’s wrong with them through trouble codes. Deciphering these codes requires the service manual.

Avoiding Skids on the Road

As promised, here are some useful tips for troubleshooting automotive brake systems. Don’t worry if you’re not familiar with all the terms used here. You’ll learn about them later in the article.

  • If your car pulls to one side during braking, first check tire pressure and front-end alignment. Then check for malfunctioning drum or disc brakes.
  • If disc brakes squeal when applied, the brake pads are probably worn out and need replacement.
  • If the brake pedal pulsates when pressed, brake pads or shoes might be worn unevenly and need adjustment or replacement.
  • If drum brakes make a grinding noise, the brake shoes are probably worn out or the wheel cylinder is stuck.
  • If the brake pedal seems mushy, there’s probably air in the hydraulic brake lines.
  • If the brakes automatically apply when you see a police car, check your foot for lead content.

Brake System

When Your Car Needs New Shoes

Most modern drum brakes (shown in the next figure) are self-adjusting. When the brakes are worn, the drum brakes need inspection and possibly replacement of key parts. Brake shoes need to be replaced about every 30,000 miles. You can do it.

You need to be familiar with several parts of a drum system:

  • Brake drum: The part on a drum brake system that receives pressure from the brake shoe.
  • Brake shoe: The movable part of a drum brake system that applies pressure against the brake drum. The replaceable surface of a drum brake system is the friction lining, which typically is replaced with the shoe; alternatively, what brakes step on as they’re dancing.
  • Wheel cylinder: A hydraulic cylinder at each wheel that magnifies the master cylinder’s pressure to evenly operate the wheel’s brake system. Disc brake systems have wheel cylinders, too.
  • Parking brake: A hand- or foot-operated brake that applies brake shoes or brake pads against the braking surface on a car’s rear wheels; also called an emergency brake. All cars have an emergency brake.

To repair drum brakes, follow these steps:

  1. Safely jack up your car and place stands under the axle.
  2. Remove the wheel covers and then the wheel from the car as you would when changing a tire.
  3. Remove the cap at the center of the axle using large pliers and/or a screwdriver. Remove the cotter pin by straightening the bent end and pulling the pin out from the round end. Remove the nut and washer.
  4. Carefully pull the brake drum toward you, wiggling it from side to side if necessary to loosen it. The wheel bearings and washers will come off the axle first, so catch them in your hand and set them aside. Continue pulling on the drum until it comes off the axle, and then carefully set it aside.
  5. Clean parts as needed with an old brush or compressed air so that you can see what you’re doing. Caution: Older brake shoe linings use asbestos, so wear a filtering face mask when cleaning.
  6. Inspect the inside of the brake drum for deep scratches, and the brake shoes and other parts for wear or damage. If in doubt about wear or damage, remove the part and show it to an experienced auto parts clerk.
  7. To remove brake shoes, first install a wheel cylinder clamp (from the auto parts store) to hold the cylinder together. Then remove the large return springs using a brake spring tool (from the auto parts store, of course). Remove the self-adjusting unit as needed to free the brake shoes. Finally, remove any other fasteners or components holding the brake shoes in place.
  8. Remove the wheel cylinder by disconnecting the brake line and removing fasteners holding the cylinder in place. If the cylinder is leaking or if you’re completely replacing your brake system, replace the wheel cylinder with a new one. You can rebuild it yourself or buy a rebuilt unit.
  9. Replace the brake shoes, wheel cylinder, springs, and other components as needed by reversing the earlier instructions.

Brake System

Reinstall the drum, repack the wheel bearings, and replace the wheel and tire. When done repairing all brakes, refill the master cylinder with brake fluid and bleed the brake system, as described in your car’s service manual. Finally, adjust the brakes.

Replacing Your Car’s Brake Pads

Disc brakes (see the figure showing the disc brake setup) stop your car by applying lots of pressure to both sides of a spinning disc (rotor) on which the wheels are mounted. The brake pads are held and operated by the caliper, which squeezes the pads against the disc when you press your foot on the brake pedal. Brake pads should give you at least 25,000 miles of service before needing replacement.

To repair disc brakes, follow these steps:

  1. Safely jack up your car and place stands under the axle.
  2. Remove the wheel covers, and then remove the wheel from the car as you would when changing a tire.
  3. Inspect the brake caliper, brake pads, the wear indicator, the disc, and other components of the disc brake system. If the brake pads are worn, replace them with new pads. They should be no thinner than 1/16 inch. If the brake disc (rotor) is scored (has grooves in it), take it to a brake shop for resurfacing (turning) or replace it with a new disc.
  4. To replace brake pads, use a C-clamp (which you can get at a hardware store or auto parts store) to push the piston back in the caliper. Remove the bolt(s) holding the caliper in place and move it aside. Don’t disconnect the caliper from the brake fluid line unless you plan to replace the caliper. If you remove the caliper, brake fluid will leak out. Remove the brake pads and shims from both sides of the disc. Install new pads and shims following the instructions that come with the parts.
  5. Reinstall the disc and hub assembly, repack the wheel bearings, replace the caliper and other components, and replace the wheel and tire. When done repairing all brakes, refill the master cylinder with brake fluid and bleed (remove any air from) the brake system, as described in your car’s service manual. Finally, adjust the brakes.
  6. A go-for-your-favorite-treat test drive is optional, but highly recommended.

Brake System Repairs

Masters of the Brake Universe

A brake system’s master cylinder usually doesn’t need replacement, except as an entire brake system is being rebuilt. You don’t want a 1S-year-old master cylinder trying to operate new wheel cylinders or calipers. If you replace wheel cylinders (done in pairs), consider replacing the master cylinder at the same time. On most cars, the master brake cylinder is located on the firewall on the left (driver’s) side of the engine compartment. Your car care toolbox has all the tools you need for this job.

To replace a master cylinder, follow these steps:

  1. Remove fluid from the master cylinder using a siphon. Cover painted parts near the master cylinder with rags because brake fluid can damage paint.
  2. Disconnect the brake lines from the master cylinder and plug the end of the lines to prevent leakage and contamination.
  3. Disconnect the electrical wires from the master cylinder, marking them for later identification if it’s not clear where they should go.
  4. Remove the bolts holding the master cylinder in place and remove the unit from the car.
  5. Replace the master cylinder with a new unit, reconnecting lines and wires. Refill the master cylinder with approved brake fluid.
  6. Bleed the brake system following the manufacturer’s instructions. Typically, this means having one person press on the brake pedal while another opens the bleed fitting on each wheel cylinder or caliper, in turn. Close the bleed fitting once brake fluid flows instead of air. Repeat the process at each wheel to remove air from the brake lines because air in the hydraulic system can reduce braking efficiency, and that can mean the difference between stopping in time and calling your insurance agent with another claim.

Boosters for Brakes

Power brake boosters make braking easier because they boost the driver’s foot pressure on the master brake cylinder. Some power brake boosters offer adjustments that can be made as needed. Such adjustments can be made at the top end of the brake pedal before the brake pushrod goes through the firewall to the booster. Visually check your car’s system for adjustments before replacing the booster. The car’s service manual can tell you more-if there’s more to tell. Before replacing the power brake booster, test it to find the cause of the problem. Boosters that use a vacuum might simply have a hole or break in the vacuum line to the booster. Use a vacuum gauge to test the line following the manufacturer’s instructions. In addition, many power brake booster systems have an adjustable pushrod between the booster and the master cylinder. If your car has one of these, check the manual for information on this adjustment. You can save yourself some valuable time and money.

Brake System

To replace a power brake booster, follow these steps:

  1. Locate the power brake booster on your car. It typically is installed on the engine firewall between the brake pedal lever and the master cylinder.
  2. If necessary, remove the master cylinder from the power booster. Depending on the system, you might not need to disconnect brake lines or drain the master cylinder; just remove the bolts mounting the cylinder to the booster.
  3. Remove vacuum and hydraulic lines from the power brake booster unit, marking them for easier re-installation unless you like jigsaw puzzles.
  4. Disconnect the power brake booster unit from the brake pedal arm. This typically means removing a nut or a cotter pin.
  5. Remove the power brake booster unit from the firewall. On most cars, mounting bolts fasten the unit to the firewall.
  6. Replace the power brake booster unit with an exact replacement, following the instructions that come with the part or in the service manual. Some units require adjustments before installation; others are adjusted in place.
  7. Be careful when you test your brakes. If your brakes were tired, you might find yourself kissing the windshield the first time or two you apply the refreshed brakes.

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