How to Inspect a Brake System

You know there is something wrong with the brakes on your car, but you want to be informed before you take it to a mechanic. You can inspect your brake system before you take it to a mechanic.You car will most likely have disc brakes on the front and may have either disc or drum brakes on the rear. If you have an older car, you may have drum brakes on the front. If you have a newer car you should have two brake alert lights on the dash. One will be red and one will be yellow. The yellow light is the ABS (automatic brake system) light.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Air gun with proper size socket to remove tires
• Hammer

How to Inspect a Brake System

1. Check to see if the red light is on. If the red light is on, your emergency brake could be on, you could be low on brake fluid, or the brake switch could be defective.

2. Make sure your emergency brake is off. If it is off, check the brake fluid. If the brake fluid is full and the emergency brake is off, you will need to check for a bad master cylinder. Start the car and push the brake pedal. Release slightly, then push it again. If it goes to the floor or if the brake pedal feels really low, you most likely have a problem with the master cylinder. If the brakes feel ok (they should not go more than about halfway to the floor), then you may have a bad brake light switch.

3. Check to see if the yellow ABS light is on. If the ABS light is on, you have a problem with the ABS system. The ABS system is comprised of the ABS module, the control module and sensors for the wheels. The ABS module is usually found near the left fenderwell in the engine compartment. On some cars, it may be near the right fenderwell in the engine compartment. You can identify the ABS module because it will have brake lines running to it. If you have four wheel ABS, there will be eight brake lines going to the ABS module. If you have two wheel ABS, there will be four brake lines going to the ABS module. The control module is attached to the ABS module. The sensors are near the wheels. The two common types are a round smooth sensor with a wire attached to it and a round sprocket type sensor with a magnet. The magnet picks up a hall effect as the wheel spins. It senses the speed of the wheel. When you hit the brakes, if one of the wheels slow faster than the other wheels, the ABS system releases the brakes on the tire that is getting ready to lock up, then puts the pressure on the brake on that wheel again, therefore keeping the wheel from locking up.

4. Check the actual brakes pad, shoes, rotors, drums and wheel cylinders. Remove the wheels from the car. On the front, look inside the caliper at the brake pads. The thickness of front brake pads are about one half inch when they are brand new. This does not include the metal backing plate on the rear of the pads. If they are less then one quarter inch thick, you will need to replace the front brake pads.

5. Run your fingertips over the rotors. If the edges of the rotors are thicker than the inside of the rotor, you should have the rotors turned or replaced. Also, if the rotors have deep scoring, you should have them turned or replaced. The rotors will have a number on them, usually on the front of the rotor near the wheel studs. This will tell you the minimum thickness allowable for the rotors for your car. If they are too thin after turning, you will need to replace them. A thin rotor does not dissipate enough heat, and they could warp or cause your brakes to stick.

6. Check the rear brakes, if they have pads, the same way, except that the thickness of the rear brakes when they are brand new should be around 7/16 of an inch. If they look very thin, replace them.

7. If you have drum brakes in the back, you will need to remove the drums. If the drum is “sticking” and is difficult to remove, give it a couple of good whacks with a hammer, right in the center of the drum. Don’t pull the drum completely off at first. Pull it about half way off, and feel inside to see how close to the drum the brake shoes are. If they are very close – maybe a fingernail’s thickness from the rotor, they are most likely fine. If they are further than that away from the rotor, you can try to adjust them first. If they cannot be adjusted far enough you, you will need new brake shoes. The total movement the shoes should have inside the drum should not exceed about one eighth of an inch. You will also want to feel inside the drum for scoring. If there is scoring, replace the drum.

8. Check is the wheel cylinders. You will only have wheel cylinders if you have drum brakes. Gently pull back the rubber boot and see if there is any brake fluid leakage inside. If so, replace the wheel cylinders. You can also check for leakage inside the drum, or you may see drips on the inside of the tire.

Tips & Warnings

• If the yellow ABS light is on, you can safely drive your car, until you can get it fixed. Just be aware that the ABS system will not work. You should get it to the dealer or your mechanic to get it repaired as soon as possible.
• Do not drive your car if the red light is on. Have it towed to your mechanic. There is a good possibility of your brakes failing completely, if they have not already.