Drum Brakes are often found only at the rear of the vehicle. Like the disc brake, the drum brake has two brake shoes and a piston. But the drum brake also has an adjuster mechanism, an emergency brake mechanism and lots of springs. When you apply the brake pedal, hydraulic pressure from the master cylinder pushes the two pistons inside each wheel cylinder outwards to force the brake shoes against the drums and apply the brakes.. That's pretty straightforward, but why do we need all of those springs? This is where it gets a little more complicated. Many drum brakes are self-actuating. That is as the brake shoes contact the drum, there is a kind of wedging action, which has the effect of pressing the shoes into the drum with more force. The extra braking force provided by the wedging action allows drum brakes to use a smaller piston than disc brakes. But, because of the wedging action, the shoes must be pulled away from the drum when the brakes are released. This is the reason for some of the springs. Other springs help hold the brake shoes in place and return the adjuster arm after it actuates.
The two most common problems with brake drums are worn out brake shoes and leaking wheel cylinders. Because of their hidden location inside the brake drums, wheel cylinders cannot be visually inspected unless the drums are removed. Usually this leak is discovered during a service or when changing or adjusting the rear brake shoes, when drum removal reveals an unholy mess of wet brake shoe and brake dust along with more work than previously planned for. The 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 seal.
To prevent this situation from occurring in the first place regular brake fluid flushes are required. Corrosion won't ever take hold.
When a wheel cylinder fails, it is bad news for the brakes. Fluid that seeps past the piston seals usually ends up dripping on the brake shoes. Fluid contaminated shoes can cause uneven braking and grabbing. If there is a serious loss of fluid past a leaking wheel cylinder seal, the driver may experience a loss of hydraulic pressure and brake failure. Sticking is another problem that may affect a wheel cylinder. Sometimes a piston will stick in its bore because dirt or corrosion acts like a wedge and jams it tight. If this happens, the brakes may not release causing the shoe to drag. Consequently, repairs should be performed immediately if a wheel cylinder is leaking fluid.
The rear brake shoes on most vehicles typically last twice as long as the front brake pads because the front brakes do most of the work. Front disc brakes handle up to 80 percent of the braking load. Consequently, the rear shoes wear at a much slower rate and are often ignored by most service centres until the second or even third brake job. By the time the rear drums are removed for inspection, or we service your vehicle, the car may have racked up 30,000, 40,000 or even 80,000 kilometres. That is a lot of kilometres on the original piston seals. Wear and corrosion inside the wheel cylinders may be reaching a critical point, even if no external leaks are yet visible. There is no way to tell how much life the wheel cylinders have left in them, so we always recommend replacing the wheel cylinders when doing a rear brake job.
Some customers may see this as "unnecessary" repair work, yet they would be the first ones to complain if a wheel cylinder started to leak a few thousand kilometres after their vehicle had new rear brake shoes installed. It is a fact that wheel cylinders eventually wear out, and when they do they can cause serious braking problems or even brake failure. Why take unnecessary chances when all you have to do is replace the wheel cylinders to restore the brakes to like-new condition? At Mansfield Motors, during every service the brake drums are removed and the rear brake shoes and wheel cylinders are fully inspected and the customer is advised on any repairs required either immediately or upcoming. That's why you can trust Mansfield Motors to perform the complete brake repair and remember you only get what you pay for.
Trying to save a few dollars on brakes could cost your life.