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Your Brake wheel cylinder worn out? » Read more about common malfunctions • Repair • Replacement manual
Safe braking with wheel brake cylinder hydraulics
The wheel brake cylinder as a technical component supports the brake linings. Wheel brake cylinders are found in both drum brakes and disc brakes. Their perfect technical condition guarantees a safe transmission of the braking power. Not necessarily built as a wear part, it nevertheless requires regular checking. This applies particularly to brake cylinders in drum brakes.
The power of hydraulics
The brakes of a car function according to the principle of hydraulic transmission, based on the condition that fluids cannot be compressed. Therefore, equal pressure exists throughout a closed hydraulic system. Applying the brake pedal causes a long thin cylinder to be pressed deeply into a container with relatively little force thanks to the brake booster, moving a broad cylinder outwards at the end of the brake line. This cylinder applies its force to the brake linings. The distance between linings and brake disc or drum is only several millimetres. They are pressed together with full force.
Position and construction of the brake cylinder
The construction of the wheel brake cylinder is different in disc brakes and drum brakes, although its task and function remains the same. In both cases it is a hydraulic system, open on one end and both are supplied with hydraulic oil via flexible hoses. Both have a moving piston within, pressing outwards when the brake is applied and pulled inwards when disengaged. In a drum brake, the brake cylinder sits within the brake drum. It is a small part, applying force to the brake shoes on two sides. On the front brake - always a disc brake - the brake cylinder is integrated in the brake caliper. It is larger than the one in the drum brake and has only one hydraulic piston. To prevent hydraulic oil from leaking out the wheel brake cylinders are equipped with rubber sleeves. These as well as their guides are the most important weak points of this component.
Defects of the wheel brake cylinder
The most important Achilles' heel of the wheel brake cylinder is generally its tightness. The rubber sleeves gradually become porous. Brake oil leaks out with fatal consequences for the entire brake system. The problem occurs mainly in wheel brake cylinders in drum brakes. Leaking oil impairs the brake's function. A layer of grease develops in the drum, affecting the friction force between lining and drum. Furthermore, the brake pressure dwindles and air can penetrate in the brake line. On brake discs, especially the wheel brake cylinder guides are susceptible to wear. They can swell due to rust, and as a result completely jam the brake. This problem occurred in the first model series of the Opel Corsa.
Repairing wheel brake cylinders
For drum brakes, replacement of the wheel brake cylinders is part of standard maintenance. Many spare part manufacturers offer repair sets for drum brakes, which include the wheel brake cylinder. Although it is more work, preventive replacement of this part is worthwhile. Even if the integrated wheel brake cylinder is apparently intact, parts should always be replaced simultaneously. It would be very annoying indeed, having to disassemble the brakes again because the brake cylinder is leaking again. The replacement of wheel brake cylinders on disc brakes is somewhat more complicated. Especially the guides can get stuck due to dirt, abrasion and corrosion. A removal tool simplifies disassembly of the wheel brake cylinder. Theoretically it is possible to repair a defective wheel brake cylinder by replacing the sleeves. As the complete parts are very cheap, this is hardly worthwhile. IMPORTANT: After replacing the wheel brake cylinders the brake system must be vented. On this occasion the quality of the brake fluid should be checked.
Costs for a new wheel brake cylinder
Prices of wheel brake cylinders for drum brakes start at 10 EUR (£9) for a separate component. It is however always recommended to replace the brake completely.