How to Replace a Brake Wheel Cylinder

How to Replace a Brake Wheel Cylinder

Brake cylinders are round, cylinder-shaped parts that sit at the top of your car's drum brake assembly and exert force to push your brake shoes against your brake drum, converting hydraulic pressure into friction that slows or stops your vehicle.brake wheel cylinder Over time they start to wear out, just like any other part that takes a beating, and they'll need replacement. Here at Gillingham garage we're often asked if you can replace a failing wheel cylinder by yourself, and the answer is yes – but it's not for the faint of heart. It's a job that involves disconnecting the brake line that carries fluid to the wheel cylinder, removing the old cylinder from its backing plate, connecting the new one, reattaching the brake line and bleeding any air out of the system to ensure everything works correctly.

The brake wheel cylinder has a circular base that projects through the backplate and has a pin that fits into a groove on the cylinder to stop it turning.brake wheel cylinder The cylinder itself has two pistons and two rubber cups that seal against each other under hydraulic pressure, with a spring between the two to keep them in place. If the hydraulic pistons wear out, a minute gap develops between them and the cylinder wall and brake fluid starts leaking through it. The cup-shaped seals inside the pistons are exposed to intense heat and constant brake fluid pressure, so they're the first parts of the cylinder to wear out.

Leaking wheel cylinders cause the brake pedal to feel soft and spongy and, if not replaced promptly, can also affect how well your car stops. If a seal leaks, the piston can contact and rub against the inside of the brake drum, wearing away at its friction surface and creating a rough, ragged surface that can't generate enough friction to slow or stop your vehicle. It's also likely to draw air into the master cylinder reservoir, causing the fluid level to drop and lowering its pressure, which in turn can lead to an overly-soft or even nonexistent brake pedal.

A bad or worn seal can also allow brake fluid to leak out between the cylinder and the inside of the brake drum, creating an airlock that keeps the pistons from fitting snugly in their bores. This can cause them to jerk when you apply the brakes, and may result in uneven wear on the brake shoes, or your car pulling to the side with its bad brakes.

To remove the brake wheel cylinder, you need to release the handbrake lever arm or bleed nut to free the spring clip (it's often a curved, round capital 'E'-shaped spring). Then lift it off the plate and slide off the cylinder. If the cylinder is fixed with bolts or nuts, they'll be stiff and you might have to apply penetrating oil to get them loose, but be careful not to spill any onto the brake drum. Once the cylinder is removed, clean up the backplate and wire-brush the pipe unions or nut(s) to remove any grit or rust. You'll also need to renew the gasket under the cylinder if it's leaking.

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