The majority of cars in the road today use disc brakes on the front wheels and drums brakes on the rear. The hydraulic part of drum brake actually at the wheel is called a wheel cylinder. When you push your brake pedal you’re pressing on a piston in an item called the brake master cylinder that makes pressure in the brake system. That pressure forces another set of pistons in the wheel cylinders out against the brake shoes, they push on the drums and, hopefully, you come to a stop.
Here’s a shocker: Any moving part wears. The pistons in your wheel cylinders have seals on them that wear as they move. If your brake fluid gets contaminated by moisture they can corrode (That’s one of the reasons why brake fluid flushes are occasionally recommended), making the surface rough and accelerating wear.
So, how do you tell if the wheel cylinders are leaking? The first thing you might notice is the brake pedal slowly dropping to the floor when you press on it, but that can also be caused by a worn master cylinder. If you find yourself having to refill the brake fluid reservoir more than about once a year and you don’t see any fluid at the back of the master cylinder then you may well have a leaky wheel cylinder. Look under the car at the back of the wheels toward the center, it shouldn’t look wet. If it does, get to your repair shop and have it checked out. It could be something else but that’s the first visual proof a driver would have of leaking cylinders.
A couple times a year you should have your repair shop do a wheels-off brake inspection. As part of that inspection the technician will look at your wheel cylinders for early signs of problems and tell you about the needed repair. Once the cylinder stars leaking you’ll probably have brake fluid on your brake shoes and they’ll need to be replaced as well. So catch it early and avoid the extra expense.
From your local Mechanic, All Tune and Lube Total Car Care. Complete Auto Repair and Maintenance