Disc brake service the right way

Aug. 28, 2014
And when it comes to performing routine disc brake services, giving your customer their money’s worth (and avoiding unnecessary comebacks) requires attention to detail.  

When was the last time you looked at your work from the consumer’s point of view? A recent repair to my personal Toyota Corolla (a fine 2007 vintage bare-bones sedan) put a $350 hole in my wallet for a battery and alternator replacement.

And I did the diagnosis and repair myself.

For many of my neighbors, $350 represents a large portion of their weekly income, and the last thing they planned on spending that money on was a car repair. That’s a fact of life we in the business know all too well. Spending on needed repairs is not high on the list of preferences for most consumers, and spending that money on preventative repairs ranks even lower. So when they do, they expect their money’s worth.

And when it comes to performing routine disc brake services, giving your customer their money’s worth (and avoiding unnecessary comebacks) requires attention to detail.  

In the Lot
“Customer requests complimentary brake inspection.” How many of those repair orders have you been assigned? In all the shops I’ve ever worked in, I’ve never had a customer take time out of their day just to have their brakes looked at. There always is an underlying reason, usually noise or pedal feel, that brought them into the shop.  Make sure your service writers get the whole story or that simple courtesy brake check may miss the real problem that brought them to you.

Once I have the repair order in hand, I head out to the car. Over the years, I’ve developed certain habits that I perform on every car before bringing it inside. Notice the operation of all warning indicators during the bulb check. Are any staying on that shouldn’t be? If so, make a note of it now. I also like to check the operation of all the interior controls to see if there are any hidden issues I should know about. Before starting the car, I like to pump off any accumulated vacuum in the brake booster (that should only take a few pumps of the pedal) and get a feel for the brake pedal’s firmness and height. I also hold light pressure on the pedal for a few minutes to see if it tries to sink down, indicating a loss of pressure somewhere in the system.

Next, while still holding light pressure, I start the car and see if the pedal drops slightly as the booster vacuum builds. With some confidence that the hydraulics haven’t gone south at this point, it’s time for a short test drive.

First, I want to confirm the customer’s underlying complaint. Most of my work orders, for example, would only say there was a “noise” and not much else. But you and I know that brake systems can produce a few different noises and they all have their own unique causes.

Grinding, or that sickening metal-to-metal sound, can be bad enough to make your teeth hurt and is a pretty obvious indicator that whatever friction material the pads originally came with is long gone. The question is not whether or not a repair is needed, but how extensive the damage is and what is it going to take to make it all right again. If I hear this noise, the rest of the test drive is cancelled and I head for the bay.

Squeals are generally caused by one of two things. First, it might be coming from a brake wear indicator and the squeal is trying to inform the owner that he’d better take his car in pretty soon or he’s going to begin hearing that grinding noise instead. Personally, I think this type of wear indicator hasn’t been practical for some time now. Drivers have their windows, and their audio systems, all the way up and can’t hear them anyway. Heck, I’ve seen systems with the pads completely gone and grinding into the calipers themselves and the owner never heard a thing! A second cause for squeal is a vibration between the pad and the disc or caliper. Many things lead to squeal and I’ll get to them once we start discussing the actual service.

Another, less common, noise is the scrub. This is a light, brushy kind of noise that I generally see related to pads that are usually not broken in properly and usually shows up as a comeback shortly after a brake service has been completed. Changing out good pads for ones with less than stellar reputations can also lead to this noise complaint.

In addition to listening for noise during the test drive, I also try to gauge performance. Is the car coming to a stop as it should? Is there any funny feel in the brake pedal? Does the car try to drift to one side or the other when the brake is applied? Does the Antilock Braking System (ABS) work under a panic stop, or working when it’s not supposed to?

Once I have a clear picture of how everything is functioning, I’m ready to return to the shop and begin my visual inspection.

In the Bay
Another habit I have is inspecting the tires, both for wear and for proper inflation pressure (even if the car comes equipped with a Tire Pressure Monitoring System (TPMS)). Brake pull and stopping effectiveness can be increased by tires that are lower than they should be. While I’m standing at each wheel, I also give them a good shake to check for obvious bearing wear and to look for loose steering and suspension components. Again, both play a role in brake performance and can impact brake operation.

With that done, I remove the wheels to take a peek at the brakes themselves. Is there any indication of overheating? Is the brake pad wear even when compared both side-to-side and inner-to-outer? Is there obvious damage to the rotor’s surfaces that would immediately require replacement to correct?

At this point, I have a pretty good idea of whether or not the customer is going to need the pads replaced and the rotors replaced or serviced. But before I go talk to my service writer (or to the customer), there’s one more thing I like to check. I strip the caliper and rotor from each side, and then I like to physically measure the endplay in the bearing assemblies with a dial indicator. Most cars today use hub bearings that can be worn out but not detectable with a simple shake of the wheel assembly, understandable when the out of limit specification is typically 0.004-inch or so. Complaints of pedal pulsation can often be traced to worn bearings, both hub and tapered, and verifying the integrity of the bearings (no matter which type is in use on the car you service) can help you properly correct an existing complaint and certainly avoid a comeback for one. Details on how to properly inspect bearings for wear can be found in the AutoPro Workshop (part of Motor Age online) and on our YouTube channel. Just enter the search term “Timken.”

Finally, with the rotors off the car (though you can perform this on the car if you want to), I measure the rotor thickness variation to determine if there’s enough material left to machine them.  Notice I didn’t worry too much about measuring lateral runout (in-and-out deflection) at this point. Had there been any pedal pulsation present, it’s almost a given it is out of specification anyway. It’s not a bad idea to mark the rotor’s relative position to the hub prior to removal, just in case you need to put it all back together again. Getting a rotor clocked off a bolt hole or two can lead to excessive runout and the creation of a new complaint.

With the visual checks done, I can write up my parts needs and hand it off to the service writer. Included on every brake service I perform is a parts request for new caliper hardware, including any anti-rattle shims used. While it does add a little bit to the overall cost for the brake service, the difference in comebacks for noise, pedal feel, and brake pad wear that results more than makes up for it.

Rotor Service
When was the last time you checked your brake lathe for accuracy? Come on, be honest! You know the cones and hubs used to locate rotors on the lathe are often used in ways they were never intended. And they’ve never been dropped on the floor, have they? If the surfaces and mating points are damaged, it is very possible to resurface a rotor that has excessive lateral runout right from the start. Better yet, consider using an on-car brake lathe. Many OEMs recommend this tool to help prevent the excessive lateral runout.

What’s the big concern over lateral runout? It leads to pedal pulsation, and it takes very little runout to make that happen. Specifications for out-of-limits lateral runout is measured in the ten thousands of an inch! Here’s what happens when lateral runout is excessive by even a little bit.

The “at rest” clearance between the pads and the rotor is very small. Rotors that have excessive side-to-side movement (those that don’t run perfectly perpendicular to the caliper) will actually rub against the brake pads as the “high” spots pass them. The rotor thickness begins to change in these spots, so when the pads are actually applied, they are forced to extend/retract in reaction to the varying dimensions. That extension/retraction is the pulsation you feel in the pedal. Your newly performed brake job will feel great on the initial test drive, but rest assured that if even a little too much lateral runout exists, the car will be coming back.

Another common contributor to excessive runout is rust build up between the components. Make sure you clean the hub mating surface and the inside and outside of the rotor hat prior to machining either on the car or off.

The final rotor finish is also a critical component to a successful brake service. Follow the recommendations of your brake lathe manufacturer on rough and final cutting techniques, including depth of the cuts and the speed of the lathe and bit feed. Finish off the rotor’s finish with a minimum No. 150 sandpaper block held to each side of the rotor for at least one minute.

Critical to avoiding squeals and contamination of the new linings is the cleaning of the rotor once you’re done. Use only a mixture of hot water and dishwashing liquid to insure all the small machining particles are removed from the rotor’s surface. The use of aerosol cleaners can actually promote the retention of these fine shards. The cold refrigerant used as a propellant actually causes the surfaces to grip the debris, while the hot water causes the microscopic grooves to open and aid in releasing that material.  Once they’re clean, keep them that way. Avoid touching them with your bare hands (leaving body oil on the surface) and certainly don’t allow grease or oil to contaminate them after cleaning.

With the rotors in place on the cleaned hubs, I like to lightly torque them in place with a few nuts I kept in my toolbox for just that one purpose. The last step in rotor service is to verify that the lateral runout is in spec. by measuring it with a dial indicator on the car. If you find it outside of spec., but have done everything right so far, simply rotate the rotor one bolt hole left or right and recheck. Usually, that’s all it’ll take to bring the reading down to an acceptable level.

Caliper and Pad Service
One tip I haven’t mentioned yet actually applies to the disassembly portion of the service. Somewhere along the line you’ll need to retract the pistons in the calipers. To avoid causing problems in any of the systems tied to the brakes (ABE, TCS, ESC), be sure you open the bleeder screw before you put your C-clamp on the piston and start pushing. Contaminants in the system tend to settle in the caliper and the pressure you are applying, even by hand, can be enough to send that debris into the hearts of tiny little solenoids that prefer that dirt not be there.

Even before that, take a look at the piston seals, those rubber boots that become more and more exposed as the piston moves outward. Look for signs of tears or failure that would allow moisture and road debris to damage the piston itself. Pushing a rusted piston past the tapered seal keeping the brake fluid on the inside could be setting the stage for a serious system leak down the road.

The caliper assembly must be free to move, too. Make sure you thoroughly inspect the caliper mounting pins and bushings for damage, and replace if necessary. If they come with the hardware kit, replace them regardless. Be sure to use an approved lubricant on them, and torque them to specification.

Also commonly overlooked are anti-rattle components. Sometimes, these are nothing more than thin metal shims that lie between the pad and the pad mounts. Pads should install with some resistance. Too much play can allow the pads to move around with minor fluctuations in the rotor’s surface or even bounce off of it when they are at rest, all leading to noise complaints (usually a squeak or squeal).

Once the caliper mount has been installed and torqued, install the pads. Do you add a touch of high-temperature lubricant to the backings and contact points? I like to certainly place some on the contact points, but the backings are a different story. Every now and then, you’ll get a pad that has an adhesive backing. No lube there! But if not, I find a small coating between the backing and the piston (on the one side) or the mounting fingers (on the other), helps control noise issues and prevent comebacks.

Remove the caliper assemblies from their hangers before reinstalling on the mounts. Oh, did I forget to mention that earlier? Whenever you have the caliper assemblies dismounted, be sure to suspend them with some form of hanger and never let their weight hang by the brake hoses. A few carefully crafted coat hangers always worked for me, and the strut springs generally made for easily accessible points by which to support the calipers. When remounting, make sure the hoses are properly routed and not kinked.  Torque the caliper mounting bolts to spec.

Back Together
If you make your living on any type of commission, this last step is an easy one to avoid. But the decrease in your comebacks may make this step a more worthwhile one to perform. What am I referring to? Breaking in the new pads.

Nearly every brake pad maker recommends some type of break in. Pads that are overheated when new can develop traits that only replacement will cure, and that’s a comeback. The easiest one for me to remember was the “30-30-30” break in procedure. That refers to 30 medium full stops from 30 mph, with a 30-second break between stops.  Yeah, it takes some time to do but if in the long run you don’t have to do a job twice?

Of course, a final test drive to verify all is as it should be and you can turn the keys back over to the owner. And go home knowing that you just delivered the most professional service you were capable of.

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