Auto Service World
News   November 2, 2015   by Jeff Taylor

Combatting brake noise

It’s too easy to blame the materials when a customer complains of noisy brakes. Sometimes we helped create the problem by not being more thorough when we installed them.

Brake Noise-1

The abutment bracket with the caliper removed, showing rust and corrosion. This is where noise is generated.

For most of us, it wouldn’t be a normal day if we didn’t have to do at least one brake job. Replacing pads and rotors have become so routine that we rarely have an issue with them anymore.

Nevertheless, once in a while, a brake job will come back to us with a noise or vibration complaint. There isn’t always a good reason for the problem, so we might be a little too quick to pin the blame on the brake manufacturer or the pad material. But there are also times when the cause can be traced back to something we overlooked.

Customers who come back with a complaint say they hear squeaks, squeals, and squawks especially when they apply the brakes lightly or with moderate force. So… what causes these noises? And why don’t they happen under harder braking?

In a nut shell, the cause is vibration. The actual brake material is resonating. Most commonly it comes from the whole pad assembly, but it can also come from the shoes. This noise is most commonly made during light application because there isn’t enough force to keep everything tight in the abutment bracket assembly. When you brake hard, the calipers clamp everything down.

If you want to prevent these annoying noise issues, it’s going to take more than just slapping in a new set of pads and hoping for the best. You’re going to have to be particularly diligent at every stage of the job.

Starting the job right

Almost all vehicles today use a floating caliper design so the issues and problems are fairly similar across all vehicle platforms and hardware manufacturers.

The first step in any brake job is disassembly… which sounds easy enough, but there are a few steps that we need to pay special attention to.

After detaching the caliper, don’t let it hang by the flex hose. Vehicle manufacturers have been utilizing smaller and lighter-weight components in an effort to improve fuel economy. Modern flex hoses are not as robust as they used to be, and the additional strain can damage them.

Once you’ve removed the caliper and its bracket from the mountings on the spindle or axle assemble, it’s time to formulate a plan of attack to ensure this brake job doesn’t come back because of noise or vibration complaint.

Abutment bracket

The abutment bracket is the piece that holds the pad. It can be a significant cause of noise if not serviced properly. Besides being subject to all the heat and forces generated during a stop, these brackets gather dust, road grime, salt, and winter chemicals.

Brake Noise-2

Brake pads with new shims and pad separators.

Start by carefully inspecting and thoroughly cleaning the area where they sit. Modern systems are designed with just enough space to allow free pad movement while still absorbing some noise-causing vibrations. The build-up of corrosion and rust often locks the pads in place, causing accelerated wear, pad failure, uneven braking, and noise.

You can use wire wheels or brushes to clean the area, resorting to gentle filing if necessary, or even blasting the area with sand or glass beads if that option is available to you. If you can’t get it clean or it is too badly corroded, replacement is obviously the best option.

The abutment pads are a throwaway piece and should be replaced whenever you replace the brake pads. These complicated little pieces of metal are designed to provide a flat smooth area for the pad edge to ride on, absorb vibration, and provide anti-rattle properties. Some even help push the pads back slightly to reduce drag (more on this in a bit). All of these critical properties are compromised when rust, heat, or fatigue takes its toll.

Pins and boots

Now it’s time to inspect and service the guide pins and their sealing boots.

The boots must not be cracked, torn, or hardened. They’re designed to allow movement while still providing protection against the elements. In extreme (but not necessarily rare) cases, the guide pins can be stuck or seized in the bracket. When this happens, replacement may be the only option. If they can be removed, they’ll need to be properly cleaned with new lubricant applied.

Brake Noise-3

Brake pads with abutment pads.

The pin holes need to be free of the old lubricant. After prolonged exposure to dust, moisture, and road grime it is probably doing more to impair free movement than enhance it!

The area that the boots attach to should also be cleaned, with all rust removed so it can provide an optimal sealing surface that will prevent foreign material from entering the pin hole. In some cases, these boots also serve as a bushing that the guide pin rides on. After too many brake applications, they deform into an oval or egg shape that causes a rattle because it can no longer hold the caliper securely.

After cleaning and visual inspections for wear and tear, the guide pins and boots should be reinstalled or replaced and properly lubricated with the correct lubricant. This is an area that can’t be discounted, and using the proper lubricant is absolutely critical. That old tub of water-attracting white grease just won’t cut it anymore. The lubricant needs to be compatible with the rubbers and seals it touches. They’re silicone-based to prevent water attraction, and have been designed to properly deal with the temperatures involved. Many brake lubricants now even contain PTFE (Teflon) to improve performance.

Anti-seize should not be used on the guide pins or boots; it’s not a lubricant, and will just ball up, gather dust, and cause a whole host of issues.

The brake rotor

In most cases a new rotor is going to be installed, but if we just machined the old one – either on the vehicle or on a lathe – it’s important to wash the rotor clean with mild soap and water to remove all the metal debris and graphite from the previous brake pads and machining process.

Yes, I said soap and water. The use of brake clean isn’t sufficient to properly remove all these leftover materials. It evaporates too fast. The leftover material can ruin even the most thorough brake service. It will be transferred to the new pads to cause noise, uneven braking, and a host of other issues. These are the symptoms we normally blame on the pad itself. Yes, replacing it will often fix the problem, but not because the old pad was no good. Rather, it gave us a second chance to get in there and remove leftover debris.

Rotor run out should also be checked; just a few thousands of an inch can cause uneven pad transfer to the rotor that will cause uneven braking and vibrations, usually within the first 5K of driving.

Brake Noise-4

Abutment pads and pad separators.

Ceramic pads are the worst for this, as the smallest amount of runout will contribute to uneven deposits of materials across the surface of the rotor.

Use the lug nuts to tighten the rotor to the clean, rust-free hub surface. Check the runout with a dial indictor. If it’s over 0.050 mm (0.002 inch) you have a problem. Just try indexing the rotor a couple of times and most times the problem will be solved. Shims are available and many times the actual hub/bearing assembly is the root issue, not the rotor. This is extreme but on a car that you’re putting three sets of rotors on, three extra minutes will potentially save you a lot of time.

… and everything else

After cleaning, lubricating, and installing new abutment pad hardware, the bracket is ready to be reinstalled on the spindle over the rotor. Some bracket fasteners are torque-to-yield and will need to be replaced. Make sure you apply the correct torque and threadlocker. Again, stay away from the use of anti-seize.

Anti-rattle clips should be replaced if they’re not part of the actual brake pad. The same goes for any pad separators which lose tension over time. These spring-like pieces not only isolate noise-causing vibration, but they push the pad back just far enough to increase fuel economy, increased pad wear, and lower pad temperatures, without affecting the brake pedal feel.

Brake pad shims are just like all the other parts. Heat cycles, rust and corrosion wears them out. If they’re separate from the actual brake pad, they need to be replaced and lubricated with the correct lubricant. Always follow the manufacturer’s instructions.

Vibration dampers are also becoming more common and they have to be properly reinstalled, or replaced if they’ve been damaged.

The obligatory road test

Burnishing in the new pads is just as important as all the other steps that we’ve been so careful to perform. And this shouldn’t be done by the customer.

Proper burnishing of the pads involves about 10 stops from 60KPH down to 10KPH under gentle and easy brake pressure. This is not a panic stop but a controlled stop that burns the pads and glazes the rotors. Allow the pads to cool between applications.

This procedure allows for proper pad-to-rotor brake material transfer and will provide optimal brake performance. If the new pads are not properly bedded to the rotors, pedal fade, and noise can be a concern.

I know what it’s like when you get busy in the shop. It’s easy to skip a few of these steps and usually you get away without any issues. But as components get lighter and smaller, even the smallest vibration is felt… and more importantly heard. Remember, most times the customer wasn’t hearing any noise before he came to you for a brake job!

Look at it this way: we always take the time to figure out a problem the second time around. But if we pay a bit more attention the first time, we can avoid the issues that cause a comeback.

Those comebacks are done for free… and they’re a productivity killer!

Jeff Taylor is a former ACDelco Technician of the Millennium and Canadian Technician of the Year. He’s the senior tech at Eccles Auto Service in Dundas, Ont.

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