Brake Repairs with Flexible Honing Tools for Rotors

Most brake shops resurface the rotors when mechanics replace the brake pads. By the time a car, truck, or motorcycle needs a brake job, the rotors may have grooves or areas of wear from the rubbing of the old pads. If a brake rotor has an uneven surface, the new pads won't make contact at the proper angle and the brakes may squeak or squeal. By turning the rotors in a lathe, brake technicians remove surface imperfections and provide the rotor with a smooth, uniform surface.

Some mechanics also turn new OEM and aftermarket rotors to improve the factory finish. As with re-turned brake rotors, the proper finish is a non-directional one where scratches on the rotor's surface extend in various directions, lowering harmonic vibrations and minimizing pad vibration and noise. A non-directional finish also helps the new brake pads to seat properly. Unless all surface irregularities are removed, however, the brake pads may skip and jump when they rub against the rotors.

How to Resurface New and Re-Turned Brake Rotors

To apply a non-directional surface finish to brake rotors, automotive technicians and do-it-yourself (DIY) mechanics use the Flex-Hone for Rotors tool from Brush Research Manufacturing (BRM). Named an Undercar Digest Magazine Top Ten Tool for 8 years in a row, the BRM rotor hone features flexible nylon filaments that are permanently laminated to abrasive globules. As testimonials from tire and muffler shops attest, this brush tool is ideal for new or re-turned brake rotors and finishes more rotors per hone.

As the Flex-Hone for Rotors guide explains, BRM rotor hones should be held securely in a chuck, collet, or similar holding device. Mount the disc rotor on a brake lathe, position all guards, and rotate the lathe between 125 and 210 RPM. Then chuck the Flex-Hone for Rotors in a variable-speed electric drill motor or low-speed air drill, rotate the rotor brush between 300 and 600 RPM, and bring the brake hone into contact with the metal surface at a slight angle.

When using the Flex-Hone for Rotors, work in towards the center and out to the edge of the rotor face, applying light but uniform pressure. Dwell time against the part - and not excessive pressure - is what produces the desired surface finish. Use the BRM rotor hone dry and work the brake hone for just 15 to 20 seconds at a time, typically 10 - 15 seconds clockwise and 5 - 10 seconds counterclockwise. To avoid overheating, do not dwell for longer periods of time.

DIY Rotor Turning Example

DIY mechanics like Blue95 of CrownVic.net, an on-line automotive forum, know that a non-directional surface finish is important, and that the Flex-Hone for Rotors is the right tool for the job. After building his own brake lathe from a McMaster Carr turntable, Blue95 set his sights on resurfacing a set of Honda brake rotors. With the Flex-Hone for Rotors chucked in a handheld electric drill, the amateur mechanic used the rotor hone for "clean-up" and "to get the surface refinished".

Like BRM's other flexible honing tools, the Flex-Hone for Rotors is not designed for heavy-duty material removal. "I checked the before and after rotor thickness with a dial caliper", the brake tech noted, "and the difference is negligible". The homemade brake lathe offered "some wobble", Blue95 reported, but the Flex-Hone® tool was "very easy to use, very controllable" and ideal for imparting a "cross-hatch or circular finish, similar to what an engine cylinder finish looks like".

Author's Note: This CR4 blog entry originally appeared in the BRM Flex-Hone Blog.