Editor's Note: This article was orginally published June 1, 2011. Some of the information may no longer be relevant, so please use it at your discretion.
Brake jobs, especially disc brake jobs, are easy, right? Remove the wheels, unbolt the calipers, and remove the old pads first. Jerk the rotors off and resurface them on the brake lathe that's been over in the corner of the shop for the last 20 years. Heck, it still has the same bits installed it originally came with! While the rotors are turning, grab that C-clamp or big set of pliers and squeeze the pistons back into the caliper bores.
Why is there fluid dripping on the shop floor?
Throw the rotors back on the car, bolt up the caliper mounts and install the pads. Nah, don't worry about that missing shim on the inner left; you don't really need that. Drop the calipers back in place, hammer them down with the impact and throw the wheels back on using the same impact. And you're done!
Some shops delegate routine brake service to their less experienced technicians, because, after all, it's just a brake job, but they don't know what they don't know, do they? While the shop might have opened up time for its more experienced techs to work on the harder stuff, often that routine brake job results in a comeback, with the customer complaining of abnormal noise, brake feel or pulsation.
In The Beginning
If the brake work is by customer request, the first step in avoiding future problems is a good interview. Why do they want the work? What problems are they experiencing? If you don't solve the reason they came in, you can bet they'll be back soon.
Follow the interview with a test drive. Take the customer along, if possible. Have them point out the issues they are experiencing, and the noises they are hearing.
While you're sitting in the driver's seat, look for any warning lights that could indicate a controller or system fault and check the feel of the pedal. Before selling them a brake service, be sure the problem really is brake-related.
Once you have all the necessary information gathered, it's time to put the car on the lift and perform your visual inspection of the braking system, but before you remove the wheels, open the hood and check the fluid level.
The hydraulic circuit is a closed system; the fluid has to have gone somewhere if the fluid level is low. Often, it's due to normal pad wear. As the caliper pistons move outward, the space behind them has to be filled.
That's the whole idea behind the fluid level sensor in the master cylinder. As this normal process continues to the point the pads are worn enough to require replacement, the fluid level in the master will drop low enough to trigger the sensor (or switch) and turn on the instrument cluster warning light. Never add brake fluid during a maintenance service. By adding brake fluid, you are covering up the fact that the pads are wearing, and the light won't come on before the owner has worn the pads to the backing plates, usually resulting in a much more expensive repair.
Brake Fluid Service
According to Chuck Kennedy, Bendix technical training, contaminated fluid is one of the top causes of hydraulic modulator failure (HCU).
"Clean fluid is the key," he says. "Removing solid particulates that could clog hydraulic components is crucial. The old style flush equipment simply takes the fluid in the master cylinder and pushes it out the calipers and wheel cylinders. If there is contamination in the reservoir, this can create serious issues."
So what does Kennedy suggest?
"Removing the fluid from the reservoir and making sure (the reservoir) is clean before adding fresh fluid will help keep the contamination from spreading into sensitive areas. Then the fresh fluid can be bled through the rest of the system," he says. "To ensure a complete change, it might be necessary to use a scan tool's bidirectional controls to bleed the HCU."
When should that fluid be changed? Brake fluid is hygroscopic, meaning it absorbs moisture. As the moisture content builds, the boiling point of the fluid drops. This can reach a point where braking causes the water in the system to boil out, resulting in a loss of (or spongy) pedal.
All the experts I asked recommend, at the least, using test strips to measure the moisture content. Strips also are available to measure copper content, an indicator of the condition of the anti-corrosion additives in the fluid. Like any other fluid in the car, brake fluid is not designed to last forever.
"ACDelco recommends DOT 3 and DOT 4 systems be flushed every two years to protect other system components and maintain a safe wet boiling temperature," says Keith Collette, ACDelco aftermarket product service specialist. "Moisture content also can be measured with an electronic tester."
"These testers are more expensive than the test strips but are not subject to contamination issues that might occur with the strips," Kennedy adds.
That's not the only way contaminants get into delicate areas. Tony Carter, Tenneco product marketing manager for Monroe brakes, says, "Simply pushing the pistons back up (into their bores) can certainly save time, but that's likely to force some contaminants back into the system." When retracting the pistons, open the caliper bleed screw and allow the fluid to drain off into a waste container.
"Always bleed the system as part of a brake job," he advises.
More Tips
With the pads removed, take a look at the wear between them, and the condition of the shims and hardware. Are the pads wearing evenly? Inner pads that wear faster than outer pads might indicate a binding caliper piston or worn piston seal. The piston seal not only keeps the high-pressure fluid in, but it also acts as a return spring for the piston. Outer pad accelerated wear often means the caliper assembly is not moving freely, requiring a closer inspection of the slide pins.
"Reusing hardware can be a real invitation to trouble," says Carter. "Corroded hardware can cause a lot of performance issues, and springs lose their 'memory', so you're not getting precise movement of the pad."
ACDelco's Collette agrees, adding, "ACDelco has found excessive noise and vibrations resulting from not replacing the brake hardware kit and reusing the worn hardware components." Improperly installed brake pads, loose or broken shims, and improper rotor finish also are common causes for brake related comebacks.
"Sometimes, cleaning or replacing certain critical components is overlooked. Leaving in components that show signs of wear or surface indentations can cause excessive movement which opens the door for noise issues," offers Kennedy.
Another important step in avoiding comebacks is choosing the right replacement pad.
"Linings not designed to OE specifications may not repair the vehicle to comply with the Federal Vehicle Safety Standards. It is important to replace the brake pads with those that emulate OEM specifications," cautions Collette.
Monroe's Carter says, "There are cases, including the Monroe Brakes product line, where the brake manufacturer offers a choice based on what their engineers have determined will offer the right blend of stopping power, longer pad life and noise-free braking. In our case, however, we always identify which technology was OE so the technician has an understanding of what the vehicle manufacturer preferred."
What about the rotors?
Pedal pulsation and noise are two common results of improper rotor service. All the experts agreed that resurfacing is only required if the rotor fails the specifications for surface finish, run-out or thickness variation and will remain within discard or machine-to specifications.
"Rust rings, small grooves or ridges, and friction material/contaminants embedded in the surface need to be removed," Kennedy notes. "A dial indicator and micrometer can find issues a visual inspection will miss. Noise, pulsation, dust, performance and life expectancy of the brake parts can be affected by the way it starts out in the beginning."
Pulsation is the result of rotor thickness variation, and this variation can occur when the initial assembled lateral run-out is excessive. Each time the "high spot" passes by the brake pads (with the brakes released), the pad wears a bit more from the rotor. This process continues until those spots are thinner than the others, and creates a wavy surface the pads must follow when applied, resulting in the pulses felt in the pedal.
An often overlooked contributor to pulsation is the condition of the hub and wheel bearings. "Thorough cleaning of the hub assembly is critical to prevent issues with runout. So are checking the hub flange for run-out and the hub bearing for play," Kennedy says. Using an on-car lathe to resurface (if needed) also can help reduce or eliminate the impact of stacked up tolerances. Collette tells us, though, that proper cleaning of the hub, rotor and wheel mating surfaces is still just as important when using this method.
Another often forgotten step is proper rotor prep and cleaning after machining. All agreed that the rotor should be finished off with a non-directional surface. To remove the high spots and small cuttings left over from resurfacing on your brake lathe, use a piece of 130 to 150 grit sandpaper and a sanding block to sand the rotor surface for about a minute per side.
Then clean the rotor with a mild soap and hot water to remove any remaining metal dust. Do not use an aerosol solvent that leaves a film on the rotor surface. A good cleaning will prevent metallic debris from reaching the new pad's friction material, and that will help prevent future comeback complaints for noise.
Last, be sure to torque the wheels during reinstallation. Use the same three-step procedure you would for any other critical component. Hammering it down with the impact gun is another sure way to create the potential of a future comeback.
Additional assembly tips
With the rotors and new pads ready for installation, take a moment to follow these additional tips provided by our experts.
"Technicians can perform the most precise and thorough brake job, but still may encounter noise and vibration problems if they don't use the right type or amount of lubricant," Kennedy cautions.
Be sure to inspect and lubricate all sliding surfaces and pins. That includes a light coat of a lubricant specifically designed for the demands of disc brakes applied to the pad backing and shims.
"This allows the shims to withstand normal brake pad movement without damage and helps dampen vibration," adds Collette. "Be sure to not get any on the friction material."
That includes touching the friction material with your bare hands. Greasy hands and even the oil from your skin, can set up a future noise complaint from your customers.
Seating new pads is another overlooked step. But here, recommended procedures vary a bit. A good general procedure to follow is to make 20 to 30 moderate stops, from 30 mph to 0 mph, while allowing about 30 seconds between stops to let the pads cool. Taking the time to mate the pads to the rotors will enhance performance, reduce noise complaints, and provide the best life possible for the replacements you use.
Nobody likes a comeback, especially one you can prevent. Follow these small but important steps when servicing disc brakes and watch those comebacks, and not the brakes, fade away.
