There's often more to brake problems than the brakes themselves.
Anti-lock braking systems (ABS) have been around for more than 20 years, and Uncle Sam says that by 2012 all new cars and trucks will have mandated stability control. Scanners, oscilloscopes and digital volt-ohmmeters are now everyday diagnostic tools. But braking still is a matter of using friction materials to grip a rotating disc or drum.
Despite all the sophistication of modern vehicle braking systems, the majority of customer complaints still involve pedal feel, pulls, noise and friction-material wear. Though at times the blame for these conditions may lie with the fancy stuff, you'll invariably save time by starting your investigation by assessing the basics – not just in the brake components themselves, but in related systems, too.
Which is it?
It sometimes can be hard to tell if a pedal-feel issue is caused by the ABS or something more routine. For example, if a customer's 1993-94 Taurus or Sable has a low pedal, is it because of an "ordinary" abnormality like brake fluid bypassing the master-cylinder piston? Or could there be an ABS problem – perhaps a hang-up within the valve block in the HCU?Here's "Troubleshooting 101" rule No. 1: look up TSBs. In this case, Ford bulletin 94-5-5 says it's not too hard to tell the causes apart. Start by disconnecting the return hose at the bottom of the brake-fluid reservoir; plug the reservoir port and keep the hose above the HCU to minimize spillage. Then, get ready to catch fluid that may come from the line as an assistant begins depressing the brake pedal while you watch the hose.
Ford says that if brake fluid essentially stays in the upheld hose as the pedal passes its usual applied height, it's bypassing in the master cylinder, which needs replacement. But if the fluid begins flowing out of the hose, the valve block's NG (No Good).Monitoring Tire Pressures
An early lesson in "Brakes 101" is that deceleration pulls aren't always caused by brake problems. Suspension abnormalities like a weak spring or shock, worn ball joint, tie-rod end or bushing, or internal tire problems/uneven inflation are all potential causes of pull. Sticking with tires, if inflation is even, sometimes swapping tires side-for-side makes the pull swap directions or disappear entirely, indicating a tire problem.
Federal regulations have required that all cars and light trucks (without dual rear wheels) be equipped with tire pressure monitoring systems (TPMS) since August 2007. You might think one part of troubleshooting pull has been simplified. If the vehicle has TPMS and there's no dashboard indicator warning of uneven tire pressures, they must be OK, right?
Not necessarily. Bill VandeWater, director of consumer products and technologies at Bridgestone Firestone North American Tire, says there are some very good reasons you don't want to scrap your tire pressure gauge and start relying on a vehicle's TPMS. And not just for brake troubleshooting.
VandeWater says two problems make TPMS unreliable as a troubleshooting tool: warm-up period and degree of accuracy.
Regarding accuracy, he points out that the federal rules only require that monitoring systems warn the driver if any tire's pressure drops 25 percent below spec. In some cases, a pressure loss may be enough to induce a pull but not enough to light the system's warning light. As for the warm-up period, because inflation readings change as a tire heats up, TPMS isn't required to report on pressure readings for the first 20 minutes after the vehicle is started. If the customer lives near your shop, the system may not even be up and running when you're evaluating their car or truck.
Avoid the Wrong Pads
We're not talking about the brand or quality of the pad. If you're getting frequent complaints about noisy and/or dusty brakes after you've done pad replacements, you may be choosing the wrong type of friction material for most of the vehicles you're servicing. Consider the results of informal surveys taken at the beginning of Bendix brake seminars. Jay Buckley, manager of technical training for Honeywell Friction Materials, says that almost three-quarters of technicians say they install semi-metallic pads in almost three-quarters of the vehicles they service. Do the math: If these figures hold for the entire industry, it means that right now, semi-mets are being installed a bit more than half the vehicles having their pads replaced.
The problem is that more than 60 percent of today's new cars and light trucks are factory-equipped with ceramic disc brake pads. In fact, says Buckley, more than half of new vehicles have been using ceramics long enough that most vehicles now on the road should have their pads replaced with good-quality ceramic pads to deliver similar characteristics to OE.
This can make a real difference. In broad terms, semi-metallic pads offer excellent fade resistance, but they're hard. This may help them resist wear, but it means they may also take a toll on rotors (leading to the production of dust) and tend to produce noise. Meanwhile, ceramics' relative softness tends to result in quieter operation and makes them wear rotors less aggressively, leading to less noticeable dusting.
Granted, proper engineering and formulation can mitigate the worst of a pad type's tendencies. And when engineers design a vehicle's braking system, they take these characteristics into account, taking advantage of a pad type's advantages while minimizing its negatives. Still, there are times when a pad-type change is in order. For example, switching to semi-mets for the hot-shot driver whose habits lead to brake fade (and points on his license) can make sense, even if the tradeoff is some dust or noise. But most often you're better off using the type of pad the manufacturer originally installed. It shouldn't be hard to find out which kind the factory used. Mainstream aftermarket suppliers usually list the OE replacement composition in their printed and online catalogs.
Using Your Senses
While it's true that no brake technician can make a living today without electronic tools and training, basic, everyday tools and the experience you've acquired also remain vital in troubleshooting brake malfunctions. So do your senses. Here are a couple of cases when open eyes, ears, etc. are your strongest assets.
Spot two-footed drivers by watching. Often in troubleshooting, the first component you need to evaluate is the customer. You can do this by riding along on a test drive, letting them demonstrate the condition — and by watching how they use the brakes.
For example, several ABS-equipped vehicles will cancel operation and illuminate the malfunction indicator light (MIL) if the electronic control unit receives an extended "brake apply request" with the vehicle under power. There may be nothing wrong with the equipment; a driver who never completely removes his left foot from the brake pedal could be initiating on ongoing brake apply request, tripping the MIL (and wearing pads/shoes, rotors/drums), while applying the accelerator with his right foot. You'll chase your tail trying to find something wrong with this driver's car!
Watch and listen to prevent "new" problems during service. Some conditions may seem to a customer to be brake-system problems, but they'll never show up when you inspect their brakes because they're not in the brakes. This means you'll get no chance to fix them unless you somehow learn about them. Avoid misunderstandings by collecting baseline information about the vehicle before you start work. This is another instance where test drives can provide valuable information – information you're in a better position to interpret than the average customer.
This isn't only true when you're preparing to fix something; it's also often the case with routine work, like a friction replacement. For example, a customer who notices a front-end "clunk" when stopping may become irate when he picks up the car because of his inflated expectation of what a hang-and-turn job can accomplish. He may think this routine maintenance job will fix any defects involved in any facet of braking. But if you find out about the clunk beforehand you can check further; you may inform him there's something else wrong (perhaps a worn CV joint) the planned work won't repair. This can lead to your scheduling the non-brake repair and avoiding misunderstandings after the work is done.
True, you can sometimes find out about such conditions – and work out repair details beforehand – by quizzing the customer. But not always. Some motorists become acclimated to flaws in their vehicle's operation and won't think to mention them. However, having some work done on their car makes them tune in again to the way it feels, and then they again notice something's wrong. And then you've got a customer-relations nightmare because they think your work induced the problem.
TPMS 101
Resetting the system
THE TECHNOLOGY INVOLVED in measuring tire pressures and sending signals from each tire to a central point can be involved. This is especially so in systems that display pressure readings for each tire, identified by corner. Complicating things further is that TPMS needs to be flexible; tire positions change, either because a conscientious customer has them rotated or because a flat shuffles the deck.
Bridgestone Firestone's Bill VandeWater says procedures vary for resetting a TPMS so it'll know which tire is where after changing, remounting or rotating tires. Take GM. Depending on model, the routine may be simple or complicated.
On a Chevy Avalanche, Suburban or Tahoe, says VandeWater, you start off by listening for a horn chirp after turning the parking lights on/off four times in four seconds. Then, deflate the left-front tire eight to 10 seconds (so the system notices the pressure drop) and listen for another horn chirp. Once you hear it, do the same in the other corners. You should hear a double chirp once all four are done. Reinflate all tires to spec and you should be good to go. That doesn't seem exceptionally complicated.
Chances are you may never get a credible TPMS reading on a Buick Century or Regal that isn't factory-fresh, however. VandeWater says the procedure is nearly impossible for a technician to perform. Here's how it's described in a Bridgestone Firestone publication.
Step 1 (after making sure all tires are inflated to spec and the ignition is switched on) is to press the red TPMS reset button in the fuse box. You should see the system indicator light flash three times. Now you have to calibrate the system. We haven't seen the GM book, but the tiremaker says calibration entails driving 30 minutes at speeds between 15 and 40 mph, then 30 minutes between 40 and 70 mph. The final step is to drive a half-hour from 70 to 90 mph! Who pays for the speeding ticket — not to mention gas and your or an assistant's time? Better work that out beforehand.
Paul Zangari is an SAE member and former ASE-certified automotive technician. Specializing in technical automotive subjects, he also hosts a car-care radio show airing in Providence, R.I., called "Drive-Thru Radio." It airs weekly on station WPRO-AM and is streamed at www.630wpro.com.
