If you have discovered a leak in one of your car's drum brakes, chances are likely the wheel cylinder has failed and will need replacing. Fortunately, replacement is a simple, inexpensive job for the average do-it-yourself car owner, and it will require only a few basic hand tools and the assistance of a friend to bleed air from the cylinder. Below is more information about how to perform this job yourself:
Tools and materials needed
replacement wheel cylinder for your make and model of vehicle
brake fluid specified for your particular vehicle model
socket set with ratchet and sockets
open-end wrench set
paper towel roll
flashlight and small mirror
1. Understand what a brake wheel cylinder does and why it leaks. Automobiles actually contain two separate types of brake cylinders: the master cylinder and wheel cylinders. The master cylinder is located beneath the hood of your car, and it is the component that provides pressure to the brake fluid which flows to each wheel. The wheel cylinders receive pressurized brake fluid, then transfer that fluid to pistons that push the brake pads against the drum walls.
Over time, the pressures inside the cylinders and the forces of friction and aging cause interior rubber seals to break down. Fluid is then able to seep past the seals and a leak develops. Replacement of the entire cylinder is the easiest and most economical repair.
2. Prepare the brake drum for the repair. Begin by jacking your vehicle in a safe, level location and position a jack stand underneath so it securely supports the affected wheel. Next, take off the wheel and remove the brake drum that covers the wheel cylinder, shoes, and other components. If the brake drum is difficult to remove, spray penetrating oil around the edges to help loosen rust or debris. Locate and detach the spring that fastens the brake shoes in place; this will allow you to remove the cylinder without any hindrance.
3. Remove the defective wheel cylinder. Using a flashlight and pocket mirror, if necessary, locate the two hex head mounting bolts that hold the cylinder to the back side of the wheel. Use a ratchet and matching socket to begin the process of removing the bolts, but only unscrew them approximately halfway. Next, use an open-ended wrench to loosen the nut holding the brake line fitting to the cylinder; slip the nut down the brake line away from the wheel. Once the brake line fitting is loosened, finish unscrewing the mounting bolts holding the cylinder to the wheel. Grasp the brake cylinder from the front side and pull it away from the wheel, and the brake line will slip free from the cylinder. Be sure to place several paper towels beneath the brake line to capture the dripping brake fluid.
4. Install the new wheel cylinder. Once the defective wheel cylinder is out of the way, you are ready to install its replacement. Align the new cylinder in the space inside the wheel, then insert the end of the brake line into the fitting; don't tighten the nut yet, though.
Next, insert the two mounting bolts through the holes on the wheel and into the cylinder. Tighten the bolts until they are secure. Finish installing the new wheel cylinder by tightening the nut that holds the brake line fitting in place. Reassemble the parts you removed and detached in step 2, except for the wheel itself.
5. Bleed the air from the wheel cylinder. Ask a helper to sit in the driver's seat and fully depress and hold the brake pedal. As they hold the pedal down, use an open-ended wrench to crack open the air bleeder valve on the back of the cylinder. Air will be pushed out of the cylinder, and the brake pedal should travel toward the floor. At that point, tighten the bleeder valve and instruct your helper to release the brake pedal. Repeat the process of depressing the brake pedal, cracking open the bleeder valve and closing the valve until brake fluid flows freely from the bleeder valve. Once that occurs, the cylinder should be filled with fluid, and all air bubbles should be removed. Replace the wheel and test the new cylinder by taking the car for a test drive.
Click here to find out more about your brakes or to find out how you can get help repairing them.