How to Check Drum Brakes - Inspecting Drum Brakes
Does your vehicle not stop as quickly as it used to? Are you hearing noise while driving or braking? Do you feel vibration in the pedal or steering wheel when you slow down? Does your car pull to one side when driving, and even more when braking? These are all signs that you may be having problems with your brake system. This system consists of many components that need to be inspected to ensure optimal braking performance and vehicle safety. In this video, we'll look at the components of the drum brake system and how to diagnose issues that you may find.
We'll begin examining the system inside the vehicle by checking the brake pedal and dashboard lights. Start the vehicle and press the brake pedal. If the pedal seems mushy it might be due to having a brake fluid leak or it could be that the brake fluid needs to be changed as it's absorbed too much moisture over time. An illuminated brake light, ABS light, or check engine light can also alert you to problems with the brake system. Now, let's cut off the engine and pop the hood to visually inspect the master cylinder for signs of leaking fluid.
Moisture around fittings or low fluid in the reservoir often indicates a leak in the system. If it's not full, add fluid. Consult your owner's manual to determine the correct type of brake fluid to add. Look at the fluid condition in the reservoir. If it's cloudy or dark it needs replacing. Many vehicle manufacturers recommend changing brake fluid every 24 months or 24,000 miles, as brake fluid will absorb moisture from the air over time which can cause corrosion and greatly reduce braking performance.
Okay, now that we've completed some basic troubleshooting, let's take a look at the drum brake system. Since we'll be working under the car it's important to observe basic safety precautions. Wear a dust mask and eye protection to protect yourself from brake dust. Do not use compressed air to clean brake parts. Always use a spray brake cleaner to keep brake dust from becoming airborne. Park the vehicle on a flat, dry surface, chock the wheels and make sure the parking brake is not engaged. If the brake shoes being inspected are on the rear of the vehicle, engaging the parking brake will lock the brake shoes into the brake drum and prevent the drum from being removed.
Place automatic transmissions in park, and manual transmissions in neutral. When jacking the vehicle, ensure the jack is rated for the weight of the vehicle being lifted, and use factory lift points which can be found in your owner's manual. Once the vehicle is lifted, support the vehicle on jack stands and not the jack. Next, we'll check the primary components of a drum brake system. When the brake pedal is pressed fluid is forced through the brake lines to the wheel cylinder that presses the brake shoes into the drum, using small pistons. When the brake pedal is released, the wheel cylinder pistons retract and return springs pull the shoe away from the drum. Over time, or under extreme use, the return springs lose tension strength and don't properly retract the shoes away from the drum. This is known as brake drag, which can cause excessive wear and unnecessary heat build up, resulting in glazed brake shoes, a condition that can cause brakes to make a squealing or grinding noise. These noises can also be an indication of brake shoes that are worn down and need to be replaced.
Now check the braking surface of the drum for discoloration caused by excessive heat or cracks. If this condition exists, the drum must be replaced. Check to see if an outer lip has formed or if there are grooves present. If either of these conditions exist the drum must be resurfaced or replaced. Even if the friction surface looks smooth there could be minor peaks or valleys that could cause new shoes to ride on high spots instead of contacting the full face of the drum, which will result in decreased breaking.
Next, check the thickness of the drum with a brake drum micrometer to make sure it is above the minimum thickness requirement. Minimum thickness specifications are stamped into the drum, usually near the mounting hub. Your local AutoZone store can help check the thickness of your drum. If the drum has worn down below this thickness, it's time to be replaced. For best braking performance, always resurface or replace drums when replacing brake shoes. Closely examine the wheel cylinder for signs of leakage. Leaking brake fluid will contaminate the brake shoe lining, causing drum brakes to grab and make more noise. This is a brake drum off of a vehicle to make it easier for you to see.
Next, Take a look at your hold down springs. When these have been weakened by heat they can cause the brake shoes to vibrate and rattle. If the springs become too lose or break, they can cause more serious problems like damaging the brake drum or possibly even cause the brake system to lock up. Since weakness from heat and age can't be visually determined, it's a good practice to replace all springs and hold down hardware whenever you replace the brake shoes. This is your self-adjusting mechanism. It ensures your shoes keep their proper position in relation to the drums over the life of your brakes. Your pedal will usually travel closer to the floor when brake shoes are out of adjustment. If the adjusting cables, levers, and springs are worn, rusted, or weakened by heat, they can't keep your drums properly adjusted to maintain the correct shoe-to-drum clearance, resulting in delayed and, or reduced braking effort.
Take time to inspect all hoses for cracking, chaffing, swelling, or leaking. Also, check all steel lines for leaks, kinks, corrosion, or damage. A brake drum system is complex but still simple enough for your to troubleshoot. For my information on how to replace brake shoes, see our video How to Replace Drum Brakes, or stop by your local AutoZone for everything you need to do the job right, including expert advice. Parts are just part of what we do. Get in the zone and thanks for watching.