Understanding Brake Cylinder Piston Issues and Replacement Guide

The brake cylinder piston is situated within the brake cylinder. Often, brake cylinders dislodge because they are too small for the borehole, causing them to slip out of position.

If the borehole becomes clogged with dried brake fluid, it prevents the piston from properly settling into place.

A vehicle’s braking system must be robust and fully functional. Nobody wants to operate a car or truck with unreliable brakes.

When brake issues arise, several components need checking. One critical part to inspect is the brake cylinder and its pistons.

What is a brake cylinder piston and its role?

The brake cylinder piston is a key component of a vehicle’s drum brake system. This system is distinct and primarily operates on the rear wheel axle of a vehicle.

Inside the brake cylinder, pistons exert hydraulic pressure to engage the brakes on a vehicle’s tires. If a piston dislodges, it can lead to brake failure.

What causes brake cylinder pistons to dislodge?

It’s important to understand that a problem with the pistons typically indicates an issue with the entire brake cylinder.

Replacing the whole brake cylinder is often more practical than just replacing the piston. Additionally, when replacing a faulty brake cylinder, it’s wise to replace the one on the opposite tire as well.

Worn-out pistons no longer fit in their borehole

Pistons are crafted from metal, but they endure intense heat and friction. Over tens of thousands of miles, this wear can degrade them significantly.

When pistons wear down too much, they may slip out of the borehole, rendering the drum brake ineffective.

Pistons coated with brake fluid

Brake fluid should not leak onto the brake cylinder or other brake components. A leak can allow fluid to enter the cylinder and coat the pistons.

Once the brake fluid dries, it forms a crust on the pistons, making the borehole sticky and hindering piston movement.

Besides addressing the leak, a mechanic must thoroughly clean the brake fluid from the brake cylinder and drum.

Can you repair a brake cylinder piston yourself if it pops out?

Yes, you can attempt to fix a brake cylinder piston yourself for temporary vehicle use, depending on the tools available.

Note: Be cautious of problems after replacing pistons in a brake cylinder

To cut costs, some vehicle owners request mechanics to replace only the worn pistons in the brake cylinder. Replacing the entire cylinder is simpler but pricier.

If the mechanic uses pistons of incorrect size, they may become loose. Ensure the mechanic rechecks the brake cylinder and verifies the piston size.

Replacing the brake cylinder

If the brake cylinder and its pistons cannot be repaired, replacement is necessary. Fortunately, replacing a brake cylinder is generally affordable.

A brake cylinder piston typically costs around $50. Instead of buying just the pistons, replace the entire brake cylinder.

Hiring a mechanic to install a new brake cylinder should cost no more than $100. If charged $100 or more, you may be overpaying.

You can replace the brake cylinder yourself, but this task is complex and best suited for those experienced with vehicle repairs.

Inspecting a brake cylinder and its pistons

Several indicators can reveal issues with your brake cylinder. Before removing the tire, ensure you have a wrench and flashlight ready.

What to check for?

Excess brake fluid

If brake fluid is pooling around the brake cylinder or nearby parts, it indicates a leak in the cylinder.

Upon removing the rubber seal from the brake cylinder, there should be no brake fluid or any liquid present. Any fluid suggests the cylinder or seals are deteriorating.

Dried brake fluid buildup

Prolonged brake fluid leaks can leave grease on the brake shoes and cylinder.

You can clean the dried brake fluid after removing the brake cylinder and inspecting the pistons.

Inspect rubber seals for damage

Rubber seals flank each side of the brake piston. As a vehicle ages, these seals degrade, impeding piston movement.

Removing brake cylinder without removing shoes

Depending on your vehicle’s brake system design, you may be able to remove the brake cylinder without detaching the brake shoes.

To do this, locate the adjuster and rotate it in its usual direction.

This action shifts the brake shoes, clearing the way for brake cylinder removal.

With the brake shoes moved, disconnect the brake line and remove the cylinder from the backing plate.

Conclusion

Replacing a brake cylinder piston is challenging, so it’s often better to have a mechanic handle it. Pistons can wear out over years of use.

No brake fluid should coat the brake cylinder or drum. Always replace both rear brake cylinders for optimal performance.