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Many cars and trucks are equipped with drum brakes, even on newer models, and drum brake systems require functional wheel cylinders to work properly. If one or more of your drum brakes are failing to actuate or release, it may be time for a wheel cylinder replacement.



What are Wheel Cylinders?

Wheel cylinders hold the hydraulic pistons that act on the drum brake shoes. Think of the wheel cylinder as a drum brake’s version of a brake caliper. Many modern, front-wheel drive vehicles have calipers and discs mounted to the front and a rear wheel cylinder and drum mounted to the rear.

How do Wheel Cylinders Work?

Your vehicle’s wheel cylinders are filled with brake fluid and connected to the brake master cylinder using high-pressure brake lines. For your brakes to work properly, the brake fluid needs to be clean, and the cylinders need to hold brake fluid regardless of the pressure in the lines.

Pushing on the brake pedal actuates the master cylinder. The master cylinder increases pressure inside your vehicle’s brake lines. The pressure inside the wheel cylinder increases as well, which pushes its pistons outward into the brake shoes. Brake shoes create friction against brake drums, which brings the vehicle to a stop.

How are Wheel Cylinders Made?

Factory wheel cylinders are often made from steel castings that are then machined to their final shape. Aftermarket wheel cylinders may be made from a variety of materials, including forged steel and aluminum billets. After machining the part to its final shape, pistons, bushings, and seals are installed to complete the job. Wheel cylinders are available to fit custom applications, too.

Why do Wheel Cylinders Fail?

  • The seals inside the wheel cylinder fail due to extreme heat, oxidation, and constant exposure to brake fluid.
  • The pistons may become worn and fail to fit snugly in their bores.
  • Excessively worn brake drums may allow enough space for the pistons to slip completely out of their bores on some cars and trucks.
  • Brake line junctions become worn and threads may strip if not handled carefully.

What are the Symptoms of Wheel Cylinder Failure?

  • Brakes feel mushy or ineffective. Do not operate a vehicle with defective brakes.
  • Brake fluid leaks from the wheel cylinder.
  • Drum brakes fail to release after releasing the brake pedal.

What are the Implications of Failure?

  • Malfunctioning brakes pose a great safety risk.
  • Brakes that fail to release increase friction and reduce fuel economy.

All fluid leaks are hazardous, but brake fluid leaks are especially so because your brakes may stop working completely. If you suspect a problem with your brakes, diagnose the issue and source replacement parts or call your local Pep Boys to schedule an appointment.

If you have questions or concerns about wheel cylinders or any of your vehicle’s components, come into your local Pep Boys where we can answer any question, help you find any part, or perform any vehicle service you might need.