Drum brakes, which are still in use today on the rear of many vehicles, operate on a hydraulic basis, using brake fluid to apply pressure to pistons in the wheel cylinder, which in turn presses the brake shoes against the drum and stops the wheels.
The wheel cylinder is made up of metal housing, pistons, and seals, and is hidden away inside the drum, making it difficult to diagnose a problem unless the drum is removed. If the cylinder has become severely worn or damaged, an obvious brake fluid leak may alert you to a problem but otherwise you might not know something’s wrong until your brakes malfunction. To avoid complete brake failure, the wheel cylinder should be replaced as soon as you notice a leak.
The wheel cylinders should also be replaced when the brake shoes are being changed for a couple of reasons: firstly, it’s better to do the whole thing at once than to have to tear everything apart again if the cylinder fails after a few thousand more miles. Secondly, new brake shoes are thicker than old ones and will push the pistons back to a position where corrosion may have developed around the bore, which could cause leaks.
To make sure you’re getting a good quality brake wheel cylinder:
Quality: Make sure the part meets SAE J431-G3000 standards.
Go for a smooth sealing surface: Check for a bore finish of 5-25 RA microinches; this ensure a smooth sealing surface.
Go for the “premium” version: The difference between standard and premium wheel cylinders is insignificant, price wise, and with a premium cylinder you get higher quality metal, better seals, and a smoother bore.
Longer part life: Look for premium SBR cups and EPDM boots. These ensure long life and durability.
Corrosion resistance: Make sure the bleeder screws are plated in order to add corrosion resistance.
Match the metal: If your original wheel cylinder was cast iron, get that. If it was aluminum, likewise.
Warranty: Shop around for the best warranty. It is possible to find a lifetime warranty on this part so make sure you do your homework.
YourMechanic supplies top-quality brake wheel cylinders to our certified mobile technicians. We can also install a brake wheel cylinder that you've purchased. Click here to get a quote and more information on brake wheel cylinder replacement.