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The brakes are an essential safety feature on a car. When a problem occurs with the brake wheel cylinder, it should therefore be replaced by an experienced mechanic and handled immediately. The brake system on today's modern vehicles is comprised of highly evolved and efficient anti-lock braking systems, often applied through disk brake components. However, most of the vehicle on the roads today, the traditional drum brake system is still used on rear wheels.
The drum brake system includes multiple parts that must work harmoniously in order to efficiently apply pressure to the wheel hubs and slow a vehicle down. The brake wheel cylinder is the primary part that helps the brake shoes apply pressure to the inside of the drum, thereby slowing the vehicle down.
Unlike brake shoes or pads or the brake drum itself, the brake wheel cylinder is not designed to wear out. In fact, it's very rare that this component breaks or fails at all. However, there are times when the brake wheel cylinder can wear out sooner than expected.
When you press the brake pedal, the master cylinder fills the wheel cylinders with fluid. Pressure created by this fluid is what activates the brake wheel cylinder to the brake shoes. Since the brake wheel cylinder is made from steel (on the outer cover) but rubber seals and components on the inside, it is possible for these internal components to wear out due to excessive heat and extensive use. Trucks and larger, heavier vehicles (such as Cadillacs, Lincoln Town Cars and others) tend to experience brake wheel cylinder failure more frequently than others.
When this occurs, they need to be replaced while servicing the brake drums; you should replace the old brake shoes and ensure all components inside the rear brake drum are also replaced at the same time.
For purposes of this article, the process of replacing the brake wheel cylinder is explained, but we recommend that you purchase a service manual for your vehicle to learn the precise steps for servicing the entire rear brake system. Do not replace the brake wheel cylinder without replacing the brake shoes and turning the drums (or replacing them) as it can cause the brakes to wear unevenly or fail.
Part 1 of 2: Understanding the symptoms of a damaged brake wheel cylinder
The image above shows the interior components that comprise the typical wheel brake cylinder. As you can clearly see, there are several individual parts that must work and fit together in order for this unit to help your vehicle slow.
Typically, the parts that fail inside the brake wheel cylinder include the cups (which are rubber and wear out due to exposure to corrosive fluid) or the return spring.
Rear brakes play a vital role in slowing or stopping a vehicle. Although they typically account for 25% of the braking action, without them, the vehicle would lose control during the simplest stopping situations. Taking notice of the warning signs or symptoms of a bad brake wheel cylinder helps you diagnose the precise source of the braking issues, but also save you money, time and a lot of frustration.
Some of the most common warning signs and symptoms of damaged brake wheel cylinders include the following:
The brake pedal is depressed all the way to the floor: When the brake wheel cylinder loses its ability to supply brake fluid pressure to the brake shoes, the pressure inside the master cylinder is compromised. This is what causes the brake pedal to go all the way to the floor when pressed. In some instances, this is caused by a brake line that is loose, damaged, or broken; but the most common reason why the brakes go to the floor is because the rear brake wheel cylinder is broken.
You hear lots of noise from the rear brakes: If you hear loud, grinding sounds coming from the rear of the vehicle as you stop, it's an indication of two potential problems: the brake shoes are worn out and digging into the brake drum, or the brake wheel cylinder is losing brake fluid pressure and not smoothly applying the brake shoes.
The brake wheel cylinder may function on one side, but not the other. This causes one of the shoes to apply pressure and the other one to stay put. Since the system works harmoniously together, the lack of dual pressure can cause sounds similar to grinding or worn out brake shoes.
Brake fluid is leaking from the wheel cylinders: A quick inspection of the rear wheels and behind the brake drum typically shows that brake fluid is leaking if the brake wheel cylinder has broken internally. Not only will this cause the rear brakes not to function at all, but the entire drum is typically coated in brake fluid. When this occurs, you'll have to replace all components within the drum.
Part 2 of 2: How to buy a replacement brake wheel cylinder
Once you've properly diagnosed that the brake issue is caused by a damaged or broken brake wheel cylinder, you'll have to purchase replacement parts. As noted above, it's recommended you replace the brake shoes and springs when you install a new brake wheel cylinder, however, it's also a good idea to replace the brake wheel cylinder when you install new brake shoes anyways. There are many reasons for this. First, when you're working on the rear brakes, it's easier to rebuild the entire drum at the same time. Plus, many OEM and aftermarket companies sell entire rear drum kits, which include new springs, wheel cylinder, and brake shoes.
Secondly, when you install new brake shoes, they'll have more thickness which makes it difficult for the piston inside the old wheel cylinder to effectively apply pressure. This situation could create leaks from the brake wheel cylinder and put you in the position of having to complete this step again.
Since there are many options for buying a new brake wheel cylinder, here are a few tips for buying a replacement part. Following these guidelines ensures your part is quality built and will function for years without defects:
Make sure the brake wheel cylinder meets SAE J421-GG2000 standards for manufacturing and quality assurance. This number will be displayed on the box and often stamped on the part itself.
Purchase a premium wheel cylinder kit. You'll often find two different types of kits: premium and standard. The premium wheel cylinder is made from higher-grade metal, rubber seals and has a much smoother bore – which helps provide smoother pressure to the brake shoes. The price difference is minimal between the two versions, but the product quality of a "Premium" wheel cylinder is far superior.
Verify that the bleeder screws inside the wheel cylinder are corrosion resistant.
Match the metal from OEM: Wheel cylinders are made from metal, but often different types of metal. If you have a steel OEM wheel cylinder, make sure your aftermarket part is also steel. Make sure the brake wheel cylinder is protected with a lifetime warranty: This typically applies to aftermarket wheel cylinders, so if you go this route, make sure it's got a lifetime warranty.
Anytime you purchase replacement brake parts, always verify they are correct for your specific vehicle before attempting to remove the old parts. Also, make sure you have all new springs, seals, and other parts that come with the wheel cylinder in a rear drum brake replacement kit.
Part 2 of 2: Replacing the brake wheel cylinder
- End wrenches (metric and standard in many cases)
- Line wrenches and specialty brake tools
- New brake fluid
- Phillips and standard screwdriver
- Rear brake bleeding equipment
- Rear drum brake rebuild kit (including new brake shoes)
- Ratchet and socket set
- Replacement brake wheel cylinder
- Safety glasses
Note: Refer to your vehicle service manual for a detailed list of tools needed for your vehicle.
Warning: Always purchase and refer to your service manual for exact instructions on how to safely perform this job in your case.
Step 1: Remove battery cables from positive and negative terminal. When replacing any mechanical components, it's always recommended to remove power from the battery.
Remove the positive and negative cables from the terminal posts and make sure they don't connect to terminals during this repair.
Step 2: Raise vehicle on hydraulic lift or with jack stands. If raising the rear axle with jack stands, make sure to place wheel chocks on the front wheels for safety.
Step 2: Remove rear tires and wheel. It's recommended you replace the brake wheel cylinder in pairs, especially when replacing other rear brake components.
However, you should complete this job one wheel at a time. Remove one wheel and tire and complete the brake service on that wheel before moving to the other side.
Step 4: Remove drum cover. The drum cover usually slides right off the hub without removing any screws.
Remove the drum cover and inspect the interior portion of the drum. If it's scratched or has brake fluid on the inside, there are two things you can do: replace the drum with a new one or take the drum to a professional brake shop to have it turned and resurfaced.
Step 5: Remove the retainer springs with vice grips. There is no proven method for completing this step, but the best way is often to use a pair of vice grips.
Remove the springs from the brake wheel cylinder to the brake shoes. Refer to your service manual for the exact steps as recommended by your manufacturer.
Step 6: Remove rear brake line from wheel cylinder. Next, you'll need to remove the brake line from behind the brake wheel cylinder.
This is usually best done with a line wrench as opposed to a pair of vice grips. If you don't have the right size line wrench, use vice grips. Make sure not to twist the brake line while removing the brake line connection to the wheel cylinder as doing so may break the line.
Step 7: Remove brake wheel cylinder bolts on back of wheel hub. Typically, there are two bolts that secure the wheel cylinder to the back of the hub.
In many cases, it is a 2/8" sized bolt. Remove the two bolts with either an end wrench or socket and ratchet.
Step 8: Pull the old wheel cylinder from vehicle. After the springs, brake line, and two bolts have been removed, you'll be able to remove the old brake wheel cylinder from the hub.
Step 9: Remove old brake shoes. As indicated in the above sections, we recommend replacing the brake shoes anytime you replace the wheel cylinder.
Please refer to your service manual for the exact procedures to follow.
Step 10: Clean rear and interior of rear hub with brake cleaner. When you have a damaged brake wheel cylinder, it's probably due to leaking brake fluid.
When you rebuild the rear brakes, you should always clean the rear hub with brake cleaner. Spray liberal amounts of brake cleaner on the front and back of the rear brakes. Place a drip pan underneath the brakes when completing this step. You may also want to use a wire brush to remove excess brake dust that has formed on the inside of the brake hub.
Step 11: Have brake drums turned or surfaced and replace if worn out. Once the brakes are taken apart, determine if you should have the rear drum turned or replaced with a new one.
If you plan on keeping the vehicle for an extended period of time, buying a new rear drum is recommended. If you have never had the rear drum turned or resurfaced, take it to a machine shop and have it done for you. The key is to ensure that the drum you install on the new brake shoes is clean and free of debris.
Step 12: Install new brake shoes. After the brake housing has been cleaned, you'll be ready to reassemble the brakes.
Start by installing the new brake shoes. Refer to your service manual for steps on how to complete this process.
Step 12: Install new wheel cylinder. Once the new shoes have been installed, you'll be ready to install the new rear wheel cylinder.
The process for installation is the reverse of the removal. Follow these guidelines but refer to your service manual for precise instructions:
Secure the wheel cylinder to the hub by installing two bolts. Make sure “plungers” are installed to the new wheel cylinder.
Reattach the rear brake line to the brake wheel cylinder and attach new springs and clips in the kit to the wheel cylinder and the brake shoes. Reattach brake drum that has been surfaced or new.
Step 14: Bleed the brakes. Since you removed the brake lines and the brake wheel cylinder does not have brake fluid inside, you'll have to bleed the brake system.
To complete this step, follow the recommended steps in your vehicle’s service manual as each vehicle is unique. Make sure the pedal is firm before completing this step.
- Warning: Failure to bleed the brakes correctly will result in air trapped in the brake lines. This can result in brake system failure at higher speeds. Always follow the manufacturer's recommended steps for bleeding the rear brakes.
Step 15: Reattach the wheel and tire.
Step 16: Complete this process on the other side of the same axle. It's always recommended to complete brake service on the same axle at the same time.
After you've replaced the brake wheel cylinder on the damaged side, replace it and complete the brake rebuild on the opposite side. Follow all steps above.
Step 17: Lower vehicle and torque rear wheels.
Step 18: Reconnect battery.
Once you've completed this process, the rear brakes should be fixed. As you can see from the above steps, replacing the brake wheel cylinder is rather simple, but can be very complex and requires the use of specialty tools and procedures to make sure the brake lines are properly bled. If you've read these instructions and have determined that this might be too complex for you, contact one of YourMechanic’s local, certified mechanics to complete the brake wheel cylinder replacement for you.
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