Brake work is one of the cornerstones of the automotive repair business, so it’s important to make sure you have the right tools and equipment to service the brakes on today’s vehicles. Most shops that do brake work have some type of brake fluid flushing and bleeding equipment (a power bleeder, vacuum bleeder or injector tool), maybe a bench lathe or on-car lathe for resurfacing drums and rotors, and probably some assorted hand tools such as a drum brake adjuster, a drum puller, bleeder screw wrenches, and hopefully a drum gauge for checking drum wear, and a micrometer for measuring rotor thickness.
What many shops lack are the proper diagnostic tools for troubleshooting common brake problems. One such tool would be a basic dial indicator for measuring rotor runout when a vehicle has a brake or speed-related vibration. A dial indicator with a magnetic or clamp-style mount, and a lockable neck allows you to easily position the indicator against the face of the rotor to measure runout. Though most vehicles can tolerate 0.003” to 0.005” of runout, some are so sensitive that even 0.0015” of runout can cause a noticeable vibration.
To detect variations in rotor thickness, a micrometer can be used, but you have to check a lot of points all the way around the rotor face. Even then, you may not find much variation. But it only takes about 0.0005” of variation to feel a pulsation in the pedal. In most cases, if you can feel a pulsation when braking, the rotors need to be resurfaced or replaced.
More than 85% of all late-model vehicles are now equipped with anti-lock brakes (ABS), traction control and/or stability control. So if you don’t have a scan tool that can read ABS codes and run various ABS self-tests, you are way behind the times.
Most shops have a scan tool for engine diagnostic work, but for brake work the scan tool must have software that can also read ABS codes and run ABS self-checks. This means buying a high-end, professional-grade scan tool, one or more factory scan tools, or a dedicated ABS tester. The capabilities of a factory scan tool are hard to beat, but factory scan tools are very expensive and only work on one make of vehicle. So unless you do a lot of work on a specific make, it’s hard to justify the investment in a factory scan tool. An “all makes/all models” aftermarket scan tool is a much better choice, or a dedicated ABS tester is even more affordable if you don’t do much engine work.
For more advanced ABS diagnostics, a digital oscilloscope (DSO) or graphing multimeter is a useful tool to own for observing wheel speed sensor outputs as a waveform. Learning how to use a scope properly takes some time, but once you understand it, it can be used to detect all kinds of engine sensor problems that don’t set codes, or are too subtle or occur too quickly to be seen on a scan tool.
Another tool that can come in handy for troubleshooting brake problems is an infrared pyrometer. These pistol-like thermometers measure infrared radiation to reveal surface temperatures. A hot brake is a good indication of brake drag. Uneven heat side-to-side may indicate a frozen or sticking caliper.
Ever encounter a vehicle with a brake balance problem? Maybe it pulls to one side, or the rear wheels lockup when braking hard, or the rear brakes don’t seem to be doing much. To diagnose these kinds of problems, you need a pair of high pressure brake gauges and some fittings so the gauges can be teed into the brake lines. For checking side-to-side brake imbalance, one company makes a nice set of pressure gauges that are attached to pad-style sensors. The sensors can be installed in place of the inner brake pads to measure how much pressure each caliper is exerting when the brakes are applied.
Brake Fluid Testers
A brake fluid tester is another diagnostic tool that every brake shop should own, but many do not. Brake fluid degenerates over time and absorbs moisture. One way to “see” how much moisture is in the fluid is to use a brake “refractometer.” This is a precision optical instrument that uses the fluid’s “refractive index” to reveal its condition. Moisture alters the way the fluid bends light, making it easy to “see” the amount of contamination on a scale in the eye piece. The refractometer scale will be calibrated for DOT 3 or DOT 4 fluids.
Another way to check the condition of the fluid is with an electronic brake fluid tester. There are testers that measure the electrical resistance of the fluid, but these can often be fooled by the presence of certain additives or contaminants in the fluid. The most accurate type of brake fluid tester is the type that boils a small sample of fluid to determine the fluid’s boiling temperature. If a DOT 3 fluid’s boiling point has dropped to 312° or less, the fluid is contaminated and needs to be replaced (340° for DOT 4 fluid). Another method for checking the condition of the brake fluid in a vehicle is to use special chemical test strips. Some of these strips react to chemicals and dissolved copper in the fluid to reveal its condition. The test strips change color to indicate “good” or “bad” fluid.
For Changing Fluid
The brake fluid in a vehicle should always be flushed and replaced with fresh fluid any time major repairs are done on the brake system (new pads or shoes, replace or rebuild calipers, wheel cylinder, brake lines, etc.). Changing the fluid assures safe braking, and reduces the risk of a comeback when old fluid is left in the system. The old fluid can be removed with a power bleeder, vacuum siphon tool, an injector tool (that can do both pressure and vacuum bleeding and flushing) or by manual bleeding.
Air-operated power bleeders, electric-power bleeders and hand-operated pressure bleeders are all available for flushing the brakes. Air bleeders run off the shop air supply and use a portable tank to pressurize the brake system. Electric pressure bleeders have a 12-volt electric motor to pressurize the system. The smaller (and less expensive) hand pressure bleeders use a hand pump to pressurize the system. Various adapters may be required to connect the power flusher to the fluid reservoir cap opening on the master cylinder.
Vacuum bleeders that run off shop air or use a hand pump also can be used to pull fluid through the system rather than push it. The vacuum bleeder is attached to the bleeder screw on a caliper or wheel cylinder to pull fluid from the master cylinder. One advantage with this approach is that you don’t need an assortment of adapters for various master cylinder reservoirs.
Another option is to use an “injector” tool that can either pressure flush or vacuum bleed the brake lines. The injector tool comes in several versions including hand-operated and pneumatic. The same tool also can be used to bench bleed master cylinders, clutch master and slave cylinders and hydraulic clutch lines, to leak test hydraulic components such as automatic transmissions and ATF coolers, to bleed and flush power steering pumps, lines and gears, and to meter and inject various fluids and gases.
On some ABS-equipped vehicles, you may also need a scan tool to cycle the ABS solenoids so trapped air can be vented from the ABS hydraulic modulator unit.
For disc brake work, basic hand tools are usually all you need to remove calipers and replace pads. But on some cars, you will need specific Torx drive bits for the caliper bolts. Some type of caliper piston tool, or a large C-clamp, is also necessary to push the piston back into the caliper when replacing pads.
For drum brake work, getting a rusty drum off the hub is often the most difficult part of the job. A brake drum puller (screw-style and/or slide hammer) usually works here, as does a blunt bit for a pneumatic air hammer to help vibrate the drum loose. A large soft-faced mallet may also be needed to help persuade a stubborn drum to pop loose.
Once the drum is off, a drum gauge should be used to measure the inside diameter of the drum to determine wear, and whether or not drum replacement is necessary.
To remove the shoes and other drum hardware, some spring pliers and a hold-down spring release tool come in handy. You might also need a clamp to keep the wheel cylinder pistons from popping out.
Rotor & Drum Resurfacing
Resurfacing rotors and drums in-house can generate additional profits for a shop, and save time. But it also means investing in a bench lathe and/or on-car lathe, and having a place to put this equipment in the shop.
Bench lathes that can do both rotors and drums are a good choice, but keep in mind that the lathe is only as accurate as the person who uses it. Lathes need to be calibrated periodically so they cut true, and bits need to be kept sharp for a good surface finish. Many vehicle manufacturers approve of on-car rotor resurfacing, and say it is the preferred method because it delivers a straighter cut with much less runout. On-car lathes have automatic setup procedures, and can save time (especially on vehicles that have difficult-to-remove “captured” rotors).
Most lathes, if used correctly with sharp bits, will produce a satisfactory surface finish that meets OEM requirements. For optimum tool life and a superior finish, consider using coated carbide bits or superabrasive bits. If a nondirectional surface finish is desired on rotors, grinding attachments or a flexible brake rotor brush also can be used to buff the rotor finish.
If a car has composite rotors, and the rotors need to be resurfaced, special adapters or oversized bell caps must be used with a bench lathe to support the rotors. Otherwise, the rotors can flex causing finish problems and runout.
Finally, one last thing you need to diagnose and repair brakes today is access to up-to-date service information. Paper manuals are expensive, and in many cases difficult to obtain because so many manufacturers have gone to electronic media for their service information (CDs, DVDs or online databases). Your best options are to subscribe to an online service, or to access the vehicle manufacturer technical websites (available at www.nastf.org). Most charge a $15 to $25 fee for “short-term” access (one to three days), but some are free. The costs can be passed along to your customers on their repair bill as a necessary expense for obtaining service information for their vehicle.
Breaking the Cycle of Brake Lathe Neglect
Adapted from Lou Calka’s article in Brake & Front End magazine, August 2007
How often does your lathe let you down? Chances are, rarely. Quality brake lathes routinely give years, even decades of accurate, trouble-free service. Of course, proper maintenance of your brake lathe, just like scheduled vehicle maintenance, will extend the life of your equipment. Furthermore, a well-maintained lathe will ensure an accurate cut and the correct surface finish on each rotor that you machine.
No one wants a comeback, particularly when a brake noise or vibration could have been prevented in the first place with a correctly finished rotor.
Just as we diplomatically point out to our customers that the maintenance requirements are in the back of the vehicle owner’s manual, you might try looking in your lathe operator’s manual for recommended service procedures.
Brake lathes are subjected to metal chips, rust, brake dust and dirt. The most important maintenance is frequent inspection and cleaning. Metal chips and dust should be cleaned from the lathe daily. If they are allowed to accumulate, they can pack down and harden, particularly in a humid environment. This will make them more difficult to remove.
Cleaning should be done with a brush. Avoid compressed air as it may embed metal particles where you least want them, like into lathe bearings, or worse yet, your eyes! Furthermore, compressed air cleaning increases the potential for airborne brake dust.
The protective boots or bellows that cover the various spindles and crossfeed mechanisms should also be inspected daily. If they’re cracked or torn, highly abrasive particles will quickly find their way into the lathe with disastrous results. These boots, especially the one near the arbor, should be kept in the shop as spare parts.
Daily care should also be given to the various adapters, cones and hardware used to mount the drums and rotors to the arbor. They, too, live in a harsh environment. Dirty adapters increase the likelihood that a rotor or drum will be improperly mounted.
If you notice a tendency for the adapters to rust slightly, spray them with light penetrating oil and wipe them down thoroughly. You don’t want them to be oily; that could do more harm than good by attracting dirt and metal chips. The penetrating oil will find its way into the microscopic valleys of the metal, preventing rust and corrosion.
Nothing has a greater impact on the surface finish of a rotor or drum than the condition of the tool bit. Dull bits will tear the metal leaving a rough finish, which can cause brake noise, rapid pad wear and poor brake performance.
A quality tool bit will produce an excellent finish and last longer than the cheap stuff. This is especially important for one-cut capable lathes. Some lathes can produce a finished rotor with just one cut, but it’s not going to happen with a dull bit.
Too shallow a cut can actually shorten tool bit life by reducing the heat transfer from the bit to the rotor (or drum). The depth of cut and feed rate will have an effect on tool bit longevity. Replace bits as needed as soon as you notice a degradation of surface finish.
Some on- and off-car lathes have oil that needs to be changed periodically. They may also have grease fittings that need to be given a shot of grease. There is generally a drain plug to allow easy draining of the lathe. Check the operator’s manual for the recommended type and capacity of oil. If your lathe is belt driven, check it occasionally for condition and proper tension. Some lathe manufacturers offer “tune-up kits” for their lathes. These kits contain common wear items such as boots, belts, silencer bands, etc. Don’t forget to check silencing devices. Rubber silencing bands should be inspected for rips and tears. A silencing band that comes off during drum or rotor machining can damage the lathe, or worse yet, cause personal injury to the operator.
If you want to keep the lathe area or your shop cleaner (due to desire or necessity), an enclosure may be the answer. An enclosure is a molded plastic “box” that fits around the complete lathe. It helps keep the vast majority of dust and chips confined to the inside of the box. If your lathe is near a workbench, office or some other area that you must keep clean, an enclosure might be just what you’re looking for. Additionally, the enclosure can help improve the air quality of the shop.
Brake Lathes Faster, More Accurate
When you’re shopping for a brake lathe today, you’re going to notice several things. First, they’re faster. Second, they’re more accurate. Third, they can handle a wide range of vehicle applications. Fourth and fifth, they’re more durable than ever and easy to use. Whether you’re looking for an on-the-car or off-the-car brake lathe, you should look for the kind of extras that will best fit your needs. For example, does the lathe have a disc/drum control lockout and warning indicator light? This feature eliminates potential crashing of the machine in drum or disc modes, even with first-time operators.
Look for an auto-measurement caliper option. It instantly measures drum or rotor dimensions to determine if the drum or rotor should be discarded prior to machining.
One company says its “anti-chatter” technology oscillates the machining speed of its lathe and eliminates the building up of vibration (chatter) that can occur when machining at a fixed speed. According to this manufacturer, its lathe provides a smoother finish that prevents pedal pulsation — the number-one cause of brake-service customer comebacks. This particular feature is activated with the push of a button.
Perhaps a heavy-duty trolley with an on-the-car brake lathe on board is best for your shop. The manufacturer of this unit says it can service rotors in half the time of other on-car lathes by providing variable speed and rotational torque during compensation and machining. Technicians can resurface rotors at the fastest possible speed and change speeds on the floor, says this brake lathe maker.
Be sure to check the featured parts and options on any brake lathe you are considering. A good bench lathe, for example, can be ordered with such accessories as a Toyota rotor backing plate; 4×4 pressed hub rotor adapter; vacuum brake bleeder; double chuck kit; D-clamps; heavy-duty, three-jaw chuck; brake fluid tester; and many others.
Some of the newest on-the-car brake lathes come with ergonomically designed handles for ease of use and a built-in computer that controls the flow of information from a sensor inside the body of the lathe. This action instructs a solenoid to make fine adjustments until the lateral runout is at or below 0.001”.
Look, too, for the ability to switch from millimeters to inches with the touch of a button, and a feature that automatically allows the operator to measure the thickness of the rotor, the diameter of the drum and calculate total indicated runout.
Source: Tire Review magazine, December 2006