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Wheel Cylinder Rebuild

Rounding out wear

The easy way to visualize the difference between disc and drum brakes is that a disc brake pinches and a drum brake pushes. The disc brake caliper forces a pair of brake pads to pinch a rotating disc. The drum brake wheel cylinder pushes a pair of brake shoes out against the inside of the spinning steel drum. Both methods will scrub speed away via turning friction into heat. The key to all this speed slowing action is uncompressible hydraulic brake fluid. A foot on the brake pedal pushes this fluid up against sealed pistons inside the calipers and wheel cylinders. The problem is that brake fluid attracts moisture by its very nature of being hygroscopic. This moisture eats into the steel of the caliper or wheel cylinder and the hydraulic seal is lost. Brake failure can be the result.

Fail-Safe

Fortunately for the modern motorist, brake systems manufactured with the future in mind have a certain amount of redundancy built in. A wheel cylinder leak will usually trigger a warning light long before brake failure occurs. Usually this leak is discovered while changing out the brake shoes. Drum removal reveals an unholy mess of wet brake shoe and steel dust along with more work than previously planned for. That moisture trapped in the brake fluid has literally eaten away at previously smooth walls of the wheel cylinder and brake fluid has escaped past rubber piston inside. The way to avoid this situation from ever occurring in the first place is to flush and bleed the entire brake system of fluid according to recommended service intervals. Corrosion won't ever take hold. A leaking rear axle seal can also cause a mess. Gear oil smells like rotten eggs. Follow your nose.

Rebuild or Replace

To determine whether a wheel cylinder can be rebuilt or replaced requires a look inside. Smooth surfaces with a barely visible amount of pitting or corrosion can be honed out and rebuilt right on the axle with a rebuild kit. Run a fingernail inside the bore. If the pits feel deep and cratered, its curtains for that wheel cylinder. The bore surface is too far-gone to be repaired. Even if the cylinder isn't leaking, disassembly can reveal problems waiting to happen. Shearing off a bleed screw may also necessitate cylinder replacement after swearing subsides. The good news is as that we have moved into the future of global auto parts manufacturing. It is often much easier and only nominally more expensive to simply replace the offending wheel cylinder with a new and fully assembled unit.