Don’t let this happen to you! You performed a brake job on a vehicle a month ago, and it’s back in your shop with a noise or vibration complaint. Performing a brake job in a busy shop can sometimes lead to overlooking details that can easily result in a comeback. In this article, we discuss areas of concern to avoid customer complaints, including diagnosing and checking wheel bearing condition, rotor lateral runout, stacked runout, surface preparation and more.
There is no worse feeling for a tech than to have performed a straightforward, uncomplicated brake job and see the vehicle return with a concern or a complaint. The customer can raise his concerns immediately after the repair or in the weeks or months following.
Brake comebacks are common and the range of complaints is huge: dusty wheels, the brakes not working like the originals, etc. The list is long. But I find the most common complaints are brake noises and brake vibrations.
There are many conditions that can cause these comeback situations, including cheap replacement parts, abuse by the customer and manufacturing issues, but several can be created by the tech performing the work.
In my tenure as a tech, I have found that brake job complaints were habitually my number one comeback, but I now take a few more steps in my inspection and repair procedures to ensure that this return number is low and typically caused by a situation that I as a tech could not control.
Sound is created when something vibrates, and these vibrations are transmitted through the air, or another medium (the vehicle’s caliper bracket and spindle assembly, for example) and this vibration is detected by our ears.
Sound is something that we want to hear, noise is something that we don’t want to hear. Either way they are both created by something vibrating.
When a customer applies the brakes and the calipers clamp the pads onto the rotor, or the shoes contact the drums to slow down the vehicle, they are creating the perfect circumstances to create a lot of vibrations that shouldn’t be heard, but if it is, its unwanted NOISE!
All brakes make some form of noise. It happens when the friction material is forced onto the drum or rotor. This friction creates vibrations; not just of the pads or shoes, but the entire brake system. The original equipment (OE) manufacturers and aftermarket parts manufacturers go to great lengths to keep the braking system of our cars and trucks as quiet as possible. The use of special shims, abutment pads, retainer clips, adhesives, friction material components and other methods are commonly used to absorb the vibrations that the brake parts create, or change the noise generated to a level that we humans can’t hear.
The initial brake inspection
Any time a customer has a brake issue or a brake concern, a comprehensive visual and hands-on inspection of the base brake system and its components should be the first step, long before any parts are replaced. If simple things are missed at this stage, the result could easily be a comeback.
Looking closely at the wear of the brake materials can be an indication of a sticky caliper, binding/bent caliper pin, binding pads or even a restricted flexible brake hose. The condition of the rotors, backing plates, dust shields, brake drums, shoes, hardware, parking brake cables and all the other crucial parts need a thorough visual examination.
For hands-on inspections, I carefully push back the caliper piston to ensure that the caliper and its mounting hardware are all free and able to move properly. If they don’t move they may need some disassembly to properly diagnose what parts are going to be needed to complete a painless brake service. I also make sure that the parking brake cables and their application mechanisms move freely and fully release properly.
Corrosion can greatly affect the splash/backing plates that are designed to prevent road grime from contacting the rotor. But that’s not all these backing plates do; in many cases they hold parking brake shoes, hardware, support ABS parts and provide directional air flow for brake cooling. The visual inspection should include a close look at these parts as their replacement may be required to prevent a rubbing or grinding noise complaint or as serious a problem as premature brake fade due to inadequate cooling.
Any tech who is working in the Rust Belt where road-clearing agents are used in the winter will understand what I’m talking about when I say that checking for corroded backing plates is essential.
Many times, I have seen a backing plate that is intact and not causing any concerns, but the corrosion growing under its attaching point, (spindle/hub) forces it outward on to the rotor surface. Over the life of the brake system the moving parts slowly clear away the rust and excess metal as it builds up, but once a new rotor is installed those clearances are changed and rubbing noises often result.
I pay attention to backing plates on a number of vehicles; Honda CRVs, GMC/Chevy pickups and VW Beetles (there are many others) and either recommend backing plate/splash shield replacement during a brake repair or warn of the noise issue they may create if not replaced.
Starting the brake job
Pay attention to the simple things from the calipers to parts inside the drums that can cause noise and vibration trouble.
Simple procedures can often be overlooked and it can start when the caliper is removed and allowed to hang by the brake hose. The flex hose was never designed to hold the weight of the caliper and a simple wire hook or bungee strap should be used to support it. The internal parts of the hose can be damaged if the weight of the caliper is applied to it and this injury may not show up right away, but the damage may result in a restriction causing a pull or dragging caliper or worse, a brake fluid leak.
Both the OE and aftermarket brake parts manufacturers will tell you that many of the parts and pieces of the brake system should be replaced when preforming a brake job, not just the pads or shoes, to ensure a trouble-free brake job (many companies even show illustrations on their brake pad packaging indicating what should be changed). And this normally includes the abutment pads, pad retainers, brake pad shims, anti-rattle clips, the caliper bushings (these bushing typically last for two sets of pads) and in the drum system all the springs and hold down hardware.
The reason is simple. The wear may not be visible but these parts wear out. This is one reason many superior quality brake pad sets now include new abutment pads. Remember, these parts all started out new together and wore out together.
All the rust, scale, corrosion and road grime should be removed and the proper brake lubricant (not lithium grease) installed on the parts that require lubrication. A brake pad that is binding/seized due to rust or corrosion or flopping around because of worn out abutments or abutment pads will cause noise.
A leading cause of brake comeback noises, according to a local GM dealership, is either improper installation of caliper/pad hardware or corrosion on or under the attaching hardware parts. ACDelco specifically notes that you should never “grind the ears of the pad to get them to fit.”
It is vitally important to make sure that the caliper hardware and their brackets are restored to like-new condition to prevent future issues and comebacks.
The importance of new quality brake shims and their proper installation is also critical to attaining a noise-free brake job. The shims that contact the back of the brake pads are anything but a simple piece of steel to quiet the pads’ vibration. These are very specialized and highly engineered components of multi-layered steel, elastomeric rubbers and other compounds that are bonded together and then bent into the proper shape. The engineers will fine-tune the layers and shape to give the shim the best vibrational damping characteristics for the particular vehicle and braking system. If the shim doesn’t properly contact the back of the brake pad it will not be able to do its job correctly, and may actually create more noise than it absorbs.
If the shims aren’t already attached to the brake pad, you can test their effectiveness by dropping them on a firm surface. They should just make a solid thunk, and not bounce all around. If they bounce around and make a tinny clinking noise, they likely won’t be able to adequately reduce any noise-creating vibrations. This is a common scenario in low price point pad kits and hardware.
Most superior quality brake pads will already have a quality shim installed on the pad when you open the box. There are several reasons for this. The factory is cleaner than most shops and dirt free for proper installation. They can be riveted or peened in the proper position or the adhesive backing can be thermally activated under pressure to ensure the shim stays in place and functions as designed. Inferior quality factory shims have been known to move off the brake pad, create noise and in some cases cut into the brake rotor, something none of us wants to happen.
Before installing the brake pads, a small amount of the proper brake lubricant should be used to add an extra layer of vibration isolation between the pad and the caliper or bracket. If the pads come with two-piece shims, a small amount can be used in between them, but the lubricant must be used sparingly, not in huge blobs that could contaminate the brake material.
Excessive lubricant will melt off and be wasted or attract debris and brake dust and cause other issues and possibly noises. Proper lubing of drum brakes again calls for a dab on the shoes’ contact area on the backing plates and the star adjuster of the self-adjusting mechanism.
Proper torquing of not just the wheels but all the parts and pieces of the brake system on reassembly is important. Many parts need to be tight but not just impact gun tight.
The proper torquing of caliper brackets is essential yet not something many of us do. Take the time to look up the specs. You will be surprised how tight many need to be to prevent noises. Citing just two examples, 2014 F-150 caliper bracket torque is 184 ft.-lbs. 2010 Cadillac STS caliper bracket bolts need fresh Loctite and require 96 ft.-lbs.
Rotors/drums as the cause of the noise, vibration or pedal pulsation
If you are machining a rotor or drum, a poor finish can easily create a noise. The rotor’s machined surface finish should be non-directional and of the proper smoothness to allow the pad material transfer that creates the correct coefficient of friction. Improper machining can result in a record player effect on both drums and rotors that results in a slapstick banging noise as the shoes or pads are pulled away and released, so attention must be paid to bit condition, machining speeds and the final machined finish.
When you’re finished machining rotors or drums, they should be washed with hot soapy water (as opposed to brake clean solvents which tend to dry too fast) in order to remove any metal fragments left over from the machining process. These small particles can impede the pads/shoes bedding process and cause noise or affect the brake pedal feel and stopping distance.
Before the rotor is installed onto the hub flange it should be cleaned to ensure there is no rust or corrosion present that could affect the runout of the assembly. And before the caliper is reinstalled the rotor and hub assemblies’ runout should be checked.
To measure rotor runout: attach the rotor to the flange with all required and properly torqued wheel nuts. Then, using a dial indicator, measure the runout 1/2-inch from the rotor’s edge, by slowly turning the rotor. When performing this test, mark the high and low spots on the rotor and index the rotor location on the flange with a Sharpie. Most passenger car applications will show less than 0.002 inch. If the reading is more than 0.002 inch, remove the rotor and rotate it 180 degrees on the flange and re-measure. If it’s now in spec, you’re all set. If it’s still out of spec the root cause has to be found or a comeback could result. Excessive runout that is greater than 0.006 inch is an indication that either the hub flange, rotor flange or wheel bearing assemble may need replacement.
Why is this measurement so important? Excessive runout could lead to uneven brake pad material transfer to the rotor. Brake pad material transfer to the rotor and drum is essential for proper brake function and feel but unevenly deposited materials affect the coefficient of friction and can create a pedal pulsation. As little as 0.003 inch of runout can easily result in a vibration/pulsating pedal comeback within 5,000 miles or less due to this uneven pad transfer.
On some particularly troublesome rotor vibration comebacks, if the runout is in spec, I recommend measuring the rotor thickness variation (RTV) in six separate locations. The spec for this measurement is typically less than 0.001 inch and in many cases is zero. This procedure is time consuming, but excessive RTV or a combination of runout and RTV together can cause pedal pulsation due to uneven pad material transfer.
The use of ceramic brake materials has made runout and RTV issues much more common due to its pad transfer characteristics. Simply installing new rotors may temporarily fix or hide the issue until the pad material is unevenly deposited again.
Wheel bearings need to be properly torqued to prevent excessive runout and so does the wheel itself. Unevenly or over-torqued wheels can cause rotor distortion and these uneven deposits can result.
In a situation where you find a lateral runout condition (where a stack-up of tolerance between the rotor and hub exists), you may be able to easily correct this without replacing parts by using a tapered correction shim between the rotor and hub. These shims are available to correct problems from initial runout of 0.003 inch to 0.006 inch.
After all the cleaning, measuring, proper lubing and installing new pads and hardware, a proper road test is the final step needed to ensure a noise and vibration-free brake job that offers the proper “feel.” The pads and shoes need to be properly broken in or burnished to allow the resins in the brake material to set properly. Hard or panic stops should be avoided during this period to avoid glazing the pads by overheating the resins and forcing them to the surface. The typical procedure involves 30 smooth stops from 30 mph, with 30 seconds in-between for the parts to cool. Nice smooth stops will bed the new pads and shoes to the rotors and drums and transfer the needed friction material to provide optimal brake performance, from the first time the customer picks up the vehicle. Don’t rely on the customer to perform this break-in.
Bringing this to a quiet, vibration-free stop
It is easy to blame the pads or the rotors when you have a comeback due to noise or vibration. But when a car owner returns complaining that the brakes are squeaking or vibrating since they had their brakes done, we must drop everything to fix the issue.
“Brake job comebacks are easily avoidable when technicians keep a few best practices in mind. Proper cleaning techniques, correct installation procedures and, most importantly, choosing quality parts,” said Josh Shuck, ACDelco brake product specialist. “Installing poor quality brakes, pads and rotors is a common reason customers return. Customer returns can be significantly reduced by being selective of the products, such as choosing true OEM parts, which ensure quality, durability and exact fit.”
Most comebacks can be averted before they even start, with careful attention to details: from the initial visual inspection, the proper repair and replacement of parts, to the final proper road test.
I would like to thank ACDelco, Nick Viverios of Brake Parts Inc and Marc Stahl of Leggatt Auto Group for their help and contributions. ■
Jeff Taylor boasts a 32-year career in the automotive industry with Eccles Auto Service in Dundas, Ontario, as a fully licensed professional lead technician. While continuing to be “on the bench” every day, Jeff is also heavily involved in government focus groups, serves as an accomplished technical writer and has competed in international diagnostic competitions as well as providing his expertise as an automotive technical instructor for a major aftermarket parts retailer.
To read more by Jeff Taylor, see.