If the pedal is hard and the vehicle is difficult to stop, you may have a power booster failure or low engine vacuum.
If the pedal is spongy or soft, you may have air in the fluid. Some vehicles have hydroboost brake assist that receives fluid from the power steering pump to assist in stopping. Be sure the power steering fluid level is correct and the hoses are intact.
Visual Inspection
After the test drive, open the hood and wipe away any dirt that may have accumulated around the lid of the master cylinder. Remove the lid and observe the level of the fluid. You may be able to see through the reservoir on some applications without removing the lid. The fluid should fall between the minimum and maximum markings. If the fluid is low, it could be an indication of a leak or the brake pads could be worn.
Don’t let any fluid from the lid or your hands come in contact with any painted surface. Brake fluid damages painted surfaces. If you do accidently get brake fluid on a painted surface, flush the surface immediately with plenty of water.
Now it’s time to remove the front wheels to get a good look at the disc brakes. You may be able to see the outboard surface of the rotor and the outboard pad through the wheel, but to perform a thorough inspection, the wheel must be removed. Often a backing plate is used, which can limit visual inspection of the backside of the rotor surface and the inboard pads. Some pickups and SUVs that are not often used develop a layer of rust on the backside of the rotor, which greatly affects braking ability. This can easily be missed if the wheels are not removed during inspection.
Raising the Vehicle
To check the front brakes, you first chock both rear wheels, making sure the vehicle is in park or in gear with the parking brake applied and the engine off. If you’re using hand tools, remove the front wheel covers or center caps (if used) and loosen the wheel fasteners slightly. Carefully raise the vehicle using an appropriate method such as a floor jack placed as specified by your vehicle’s manufacturer.
When the vehicle is high enough to allow the front wheels to be removed, place jack stands under the vehicle and lower the floor jack to allow the vehicle weight to rest on the stands.
Be sure that you raise the vehicle per your vehicle manufacturer’s guidelines. The American Lift Institute (ALI) issues a guide that lists all vehicles and their lift points. Lifting information for your specific vehicle might also be available online.
A floor jack with adequate capacity should be placed at the proper lifting point for your vehicle and carefully lifted high enough to allow wheel removal. Do not use the jack that came with your vehicle to support it while servicing your brake system.
Wheel chocks should be placed on both sides of the opposing wheel when jacking up a vehicle. Also be sure that the vehicle is in park or in gear and the parking brake is applied before raising the vehicle. If you are using hand tools to remove the wheel fasteners, slightly loosen them before raising the wheel off the ground.
A jack stand with adequate capacity must be used to support the weight of the vehicle prior to beginning brake inspection or service. If the jack stand is placed under the vehicle as a safety backup and the jack is supporting the weight, it could be crushed if the jack should fail. This is referred to as “shock loading.” Jack stands are not rated for this type of load.
Remove the wheel fasteners and lift the wheel from the hub. Wheels are heavy, so be careful. Some manufacturers recommend marking the stud position and reinstalling the wheel in the same position.
Remove the wheel fasteners. Most vehicles use nuts that require one of the following socket sizes: 3/4, 13/16, or 7/8 inch or 17, 19, 21, or 22 mm. German vehicles and Saturn vehicles use wheel bolts instead of nuts, and most require a 17-mm socket for service. Some trucks and SUVs use larger lug nuts that require a larger socket. Some older vehicles have left-handed threads on the driver-side wheel studs.
If you are using hand tools, you may need to have an assistant hold down the brake pedal as you remove the fasteners to keep the wheel from spinning. Do not attempt to work on a vehicle if it is lifted unsafely. Don’t use the jack that came with your vehicle or wood blocks to support the vehicle during brake service. Only an automotive jack stand rated for the load should be used.
After the two front wheels are removed, you have a much better view of the disc brake system.
Brake Pad Inspection
The thickness of the friction material on most new brake pads is 1/4 to 1/2 inch. Every manufacturer has replacement guidelines for thickness and some states have vehicle inspections to ensure that the thickness is safe for vehicle operation. Some allow as little as 1/16 inch on bonded pads or 1/8 inch on riveted pads before the vehicle is rejected. Special tools are available to measure pad thickness on the vehicle using color coding. Some are able to obtain the actual thickness remaining without removing the pad first.
Several tools are available to measure brake pad thickness while the pads are still on the vehicle. The color-coded gauges indicate a range of thicknesses. The other tool has a scale to read exact dimensions.
To measure pad thickness, the tips of a scaled tool are placed between the rotor and the pad backing plate. The scale displays the remaining pad thickness in increments of 1/32 inch.
The color-coded “go-no-go” gauge is placed between the rotor surface and the pad backing plate like a feeler gauge. The color codes indicate whether the remaining pad thickness represents an immediate concern or not. The green gauges are the thickest and the red ones are the thinnest.
Here a color-coded gauge is in use. The yellow gauge slides in and out easily with light drag, indicating that the pad still has some life left.
Look for cracks that may affect operation or contamination from brake fluid or grease. If found, the pads should be replaced, not just cleaned. Grease can be absorbed into the pad structure. Pads can also be overheated. Generally you see evidence of this on the rotor surface in the form of blue, black, or brown heat marks or hot spots. If this found, rotor replacement is required.
Excessive uneven (wedge shaped) wear or one pad wearing more than the other could mean caliper slide issues. If the vehicle has a sliding or floating design and the outboard pad is worn more than the inboard, the slides are dirty. If the inboard pad is worn more than the outboard, the slides are seized. If you do not address these issues, the new pads will develop the same wear patterns.
Brake Noise
Unfortunately brake noise occurs from time to time. It is the most common reason that professional brake shops have vehicle “comebacks.”
Doing the job right and taking the proper steps during service minimizes the possibility of brake noise, but because all brakes vibrate and vibration can be audible, noises can happen. The goal of an automotive brake engineer is to make the