When a cute girl came into a reddit user's shop to get her oil changed, she mentioned a "slight" grinding sound coming from the ... what's that part called again?
For those of you who don't know what you're looking at in the photo above, see those ribs? They're supposed to be sandwiched between two thick pieces of metal to make a complete disc brake rotor. Oh, and there are also supposed to be pads on those calipers, which there clearly aren't.
So here's how you check to make sure your brakes are kosher.
Disclaimer: I used to work on brakes at Pep Boys, so this is a pretty broad description of brake checking based on the kinds of crappy, regular-guy cars we serviced there. Learn or laugh at your own peril.
Checking Your Brakes
Even if you have one of those open wheels that allows you to peer inside and see the brakes pretty well, the best way to assess the condition of your disc brake pads and rotors is by jacking up the car, and taking off the wheel. (Note: Front brakes always wear faster than rear brakes because they do most of the car's stopping. As such, front brake rotors are usually vented, and have fins sandwiched between the two rotor surfaces, while rear rotors are usually solid metal discs.)
- 1. If you're looking at the front brakes, put some blocks/chocks behind the rear wheels to keep the car from rolling (and if you're looking at the rear brakes, chock the front wheels).
- 2. Loosen the lug nuts on the wheel you intend to take off. Then jack up that end of the car and support it securely with jack stands. Remove the wheel.
- 3. Look at the brake pad lining. There should be at least 1/8-inch of lining material between the brake pad's backing plate and the rotor. There are (or should be, in most cases) two brake pads per caliper. If one looks a lot thicker than the other one, there's probably a problem with your brake caliper. It's supposed to slide evenly back and forth when you depress and let off the brake pedal.
- 4. Inspect the rotor. For the uninitiated, that's the disc-shaped part from which disc brakes derive their name. Each manufacturer has its own standards regarding how thick the rotor should be (they wear down over time, as evidenced by the photo at the top of the page), so you should Google what's appropriate for your vehicle and measure it to see where you're at. Discs should be a certain thickness to help dissipate heat, etc., so this is important. Also, thin discs can crack, which is bad.
- 5. While you're looking at the rotor, spin it around with your hand. If you're looking at a drive axle, make sure the car is in neutral and the parking brake (if it's connected to that axle) is off (for example, my '86 Subaru wagon is weird and has the parking brake on the front wheels). The rotor should turn more or less smoothly. Does it grab in one spot? If so, it's probably warped and should be machined or replaced. The rotors should also be more or less smooth, without deep scoring. In other words, if it looks like you could use parts of the rotor as a racetrack for a ball bearing, it's time to have those puppies machined/replaced.
- 6. While you're looking at the brakes, inspect the brake lines for leaks. See that flexible rubber hose that runs between the steel brake line attached to the frame and the brake caliper? It should be dry (i.e. not soaked in brake fluid or oil), and free of cracks.
Brakes, along with steering and suspension, are the most important parts of a vehicle as far as safety goes. So if you're unsure about any of this when you're looking at brakes, please take your ride to a mechanic to have them checked out. The point of checking them yourself periodically is to have an understanding about what's going on behind those wheels as the miles pile up on your odometer.
It's best not to have surprises, so it doesn't hurt to have a gander at your brakes when you rotate your tires, which you should be doing periodically anyway.