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What's Changed About The Brake Job?


2/15/2012
By Gary Goms

Selling modern brake service parts is a lot like making a game-winning touchdown.
 
Although I’m not a big football fan, our local team has been working its way into the playoffs. Last Saturday, the game was tied and went into overtime. With his back to the wall, our quarterback passed the ball to a receiver who was wide-open. Evidently, the attention of the opposing team had been directed elsewhere because our receiver caught the long pass, ran to the right, stiff-armed one of the defenders, and sped toward a game-winning touchdown.

Selling modern brake service parts is a lot like making that game-winning touchdown. Too often our attention is directed at selling brake friction when, in fact, our attention should also be directed at selling related parts and service tools. Although the differences between selling brake friction and related parts might appear subtle, the difference can be a game-winning touchdown on a jobber store’s bottom line.

WHAT’S CHANGED IN BRAKE REPAIRS
The differences between anti-lock braking system (ABS) on a modern braking system and that on Grandma’s ’85 Oldsmobile are significant, to say the least. The ABS is now electronically networked with vehicle stability controls (VSC), which will soon become standard equipment on all passenger vehicles and light-duty trucks. Like ABS, the purpose of VSC is to help the driver maintain vehicle control in hazardous driving conditions. Vehicle stability controls rely on lateral acceleration sensors located in the chassis to detect skids and other dangerous driving situations. ABS and VSC are integrated because the stability control computer must activate one or more wheel brakes to help the driver regain control of the vehicle.

The functionality of many systems including traction control, automatic transmission shift points, speedometer, and some tire pressure monitoring systems (TPMS) also rely on signals generated by the ABS wheel speed sensors. As with ABS, all of these systems rely on having the same tire circumference and upon brakes that apply evenly without grabbing.

In the simplest of terms, partial brake repairs on these systems pose a danger to many drivers and a liability to many shop owners. Quality brake friction is a must, so remember that, in most cases, the technician is getting just what he’s paying for when it comes to maximum stopping power, quiet operation and reduced brake dust. To better understand what it takes to maintain modern braking systems, let’s look at some of the tooling and materials requirements for restoring brake performance to the auto manufacturer’s standards.

COMPUTER SCAN TOOLS
Obviously, all of the above electronic systems are networked into the modern braking system and share information. Consequently, a professional-level diagnostic scan tool or dedicated brake service scan tool is one of the requirements for performing modern brake service. The scan tool serves three basic functions, the first being a method of locating diagnostic trouble codes in the ABS and other safety-related systems. This process is called “polling” the on-board computers for diagnostic trouble codes and other data.

The second function of a scan tool is to bleed the brakes on ABS-equipped vehicles that require that function. The third function is to display individual wheel speeds, which verify wheel sensor operating data. After the brake repair is done, many current scan tools can be used to reset the tire pressure monitoring systems (TPMS) if the tires are rotated as part of the brake repair service.

BRAKE FLUID MAINTENANCE
With the correct brake system maintenance, a modern vehicle can easily last 300,000 miles. Part of that maintenance is to replace the brake fluid at the manufacturer’s recommended intervals or at intervals consistent with local driving conditions. The reason for replacing or flushing brake fluid is because DOT 3 brake fluid recommended for most ABS units is hygroscopic, which means it attracts water molecules through brake hoses and master cylinder seals which can corrode vital parts. For this reason, a thorough brake fluid flush should be an integral part of any brake service.

While many shops still bleed air from brakes by pumping the brake pedal, keep in mind that such a practice can dislodge sediment and cause problems within the ABS unit. Vacuum flushing equipment is generally the simplest and most reliable method for flushing brake fluid and can range from a simple attachment for a hand vacuum pump to a dedicated system designed for production brake bleeding. If the internal brake system has been opened and exposed to air, a scan tool might be also be required to bleed air from the brakes.

BRAKE ROTOR SERVICE
Modern light-weight brake rotors are regarded as sacrificial parts meant to be replaced rather than serviced. As a rule of thumb, a rotor should have at least .020” of excess stock left on each side before it can be successfully resurfaced. If the rotor surface has deep wear grooves or is badly rusted, it is more economical to replace than recondition it. So it’s often cheaper to replace the rotor than to fully recondition it.

Not that any shop or jobber store should put a “for sale” sign on their disc and drum lathes. Many truck rotors are cost-effective to recondition as are many older passenger car and truck brake drums. Many of your dealer accounts have also converted to on-the-car rotor reconditioning, especially for vehicles that have “captive” rotors requiring a major disassembly of the hub and suspension for removal. On-the-car rotor reconditioning basically eliminates the set-up errors that can occur on off-car brake lathes. If your wholesale dealer isn’t doing on-car machining, it’s time to hand out some new tool catalogs.

BRAKE CALIPER SERVICE
The need for brake caliper replacements depends largely upon local climates and driving conditions. Calipers exposed to damp, cold climates and road salt should be replaced with the brake pads. In drier climates, brake calipers often require only a visual inspection for broken seals and for sticking pistons. The symptoms of sticking caliper pistons include obvious fluid leakage, uneven side-to-side brake pad wear, brake pull or grabbing, and difficulty compressing the piston back into the piston bore.

BRAKE LINES AND HOSES
When addressing the need for replacing rusted steel brake lines and cracked brake hoses, remember that modern ABS systems can apply well in excess of a thousand pounds per square inch operating pressure. Worse still, a bad brake line or hose will rupture only when needed the most, which is usually a panic stop situation. If the calipers are being replaced, it’s also good practice to replace the brake hose and perhaps the brake line connecting the caliper to the ABS unit.

MASTER CYLINDERS
Too often, technicians and amateur mechanics forget that the brake system master cylinder wears at the same rate as the calipers and wheel cylinders. A quick test for a defective master cylinder is to apply foot pressure to the brake pedal and see if the pedal sinks to the floor. If there’s no visible internal leakage at the calipers, wheel cylinders, or brake lines, the master cylinder is experiencing internal leakage caused by a rough cylinder bore and worn piston cups.

In addition, always check for fluid leakage from the back of the master cylinder bore. If the master cylinder reservoir requires a constant “topping off” with brake fluid, the cylinder can be leaking fluid into the vacuum brake booster. Another warning sign is a thick collection of sludge in the master cylinder reservoir, which is caused by excess moisture accumulation in the fluid and by contamination with petroleum-based fluids. In either case, the master cylinder should be replaced with new or remanufactured.

WHEEL BEARINGS AND SEALS
Good wheel bearings and bearing seals are essential for keeping the brake rotor or drum concentric with the axle itself. Worn wheel bearings can, for example, cause a low-speed activation of the ABS unit. Because the worn wheel bearing can no longer maintain the paper-thin air gap between the ABS wheel speed sensor and the axle shaft reluctor, false data is sent to the ABS
computer.

Similarly, worn axle shaft oil seals can contaminate a brake friction lining, which causes grabbing brakes.














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