How many times have you seen a hand-painted sign in a shop window that advertised a menu-priced brake pad replacement for “$XX.95 per axle.” Of course, a menu-priced brake replacement would be good if a simple brake pad replacement would cure all of the root causes of a brake performance complaint.
Unfortunately, menu-priced brake pad replacements are a customer comeback in the making because the customer often leaves with the same squeaking, grinding, pulsation, grabbing or pulling complaints that brought him to the shop in the first place.
For all of the above reasons, it’s always been my practice to use a simple, but effective, brake inspection procedure that takes most of the surprises out of the brake repair process. Let’s begin with the customer interview.
The Customer Interview
Because a modern braking system can be very expensive to repair, it’s doubly important to correctly identify customer concerns. Case in point, North American drivers are usually concerned with squealing and grinding noises. At the one extreme, a squealing complaint might indicate that the wear indicators are just beginning to contact the rotor. At the other extreme, a grinding-noise complaint might indicate that the brakes are operating in a metal-to-metal condition or that a wheel bearing has completely failed.
We also must “think out of the box” because an intermittent chattering-noise complaint might be caused by a premature activation of the anti-lock braking system (ABS). Over-sized tires might cause a lack of pedal response or braking power complaint, or driving many miles
on dirt roads might cause a brake-squeal complaint. See Photo 1.
The Visual Inspection
Since racing up to a red traffic light at 40 mph isn’t a good way to diagnose bad brakes, it’s better to spend a few minutes doing a preliminary inspection of the vehicle. For example, make sure that all four tires are of the same recommended size, circumference and inflation. Check the tire pressure monitoring system (TPMS) warning light for an indication of a failed pressure sensor.
As a rule of thumb, tire circumferences should be within a ½-inch of each other as measured with a flexible measuring tape. The tread patterns should also be identical to ensure equal corner-to-corner road adhesion. Due to increased leverage on the brake assembly, trucks and SUVs equipped with large-diameter tires will usually suffer a loss of braking power.
A badly worn tire on the front might indicate a wheel alignment problem that could be the root cause of a brake-pulling complaint. Tires that aren’t centered in the wheel wells usually indicate a bent control arm or broken leaf spring center bolt. Last, check the spoke alloy wheels for severe dusting. If the wheel is covered with black or rusty brake dust, semi-metallic brake pads might have been substituted for the OE ceramic pads. If metallic particles are present on the wheel, metal-to-metal contact is taking place.
Before driving the vehicle, raise the hood to check the brake-fluid level in the master cylinder reservoir. DOT 3 brake fluid normally ages to a dark-tan color and has the viscosity of salad oil. Examine the fluid closely to see if it’s contaminated with motor oil or power steering fluid. Moisture or oil contamination will thicken or emulsify the brake fluid. A low fluid level can indicate extreme disc brake pad wear or fluid leakage. Brake fluid residue emanating from the rear of the master cylinder down the front of the vacuum booster indicates a leaking rear master cylinder seal. See Photo 2.
The Parking Lot Road Test
I recommend connecting a professional scan tool before starting the engine. As the ignition is turned on, see if the orange ABS and red brake warning lights illuminate for a bulb check. If the ABS and brake warning lights remain on, the brake-fluid level might be low or the fluid level sensor might be disconnected. A red brake warning light indicates that the parking brake is engaged. If the orange ABS warning remains on after the engine starts, check the ABS module for DTCs.
If ABS codes exist, a separate diagnostic fee should be included to diagnose their cause. After capturing the trouble codes in the scan tool memory, pull up the data lines indicating wheel speed sensor activity. In many cases, a default value of perhaps 3 mph will be indicated at all four wheels. Wheel speeds should increase evenly as the vehicle accelerates. Your scan tool might also come in handy for adjusting the electric parking brake, if so equipped.
Before starting the engine, maintain light pressure on the brake pedal. If the pedal slowly sinks, it’s very likely that the master cylinder is worn. Then, apply heavy pressure on the brake pedal. If the pedal sinks, a hydraulic leak is present that makes the vehicle unsafe to drive.
