In this issue, we’ll discuss tools and equipment related to servicing brake systems. Like most service areas, there have been a lot of changes and they just keep on coming.
Q. We plan to purchase a brake lathe sometime this year and would like to know if there are any guidelines we need to follow to ensure the right finish for rotors and drums?
A. Yes, making sure rotors and drums are finished properly can be one of the biggest steps you can take against brake squeal. Before machining rotors and drums, make sure the lathe's cutting bits are sharp before each use. Check the lathe's cutting depth, speed and feed for proper setting. You can achieve an acceptable, non-directional surface for rotors by using the following settings:
- Spindle speed for the first and last cuts: 150 rpm.
- Depth for the first cut: 0.005" - 0.010".
- Depth for the last cut: 0.004".
- Cross feed per rpm for the first cut: 0.006" - 0.010".
- Cross feed per rpm for the last cut: 0.002" maximum.
Use a dampening device during machining to prevent a chatter-related rough finish. After machining, use a lathe swirl grinder or sand in a circular motion with a piece of #120 emery cloth. A word of caution: Remember that there are operating differences between the various manufacturers’ brake lathes. Accordingly, the lathe manufacturer’s recommendations should be heeded at all times. Should the spindle speed (called drive speed with on-the-car resurfacers) or crossfeed speed be excessive, you can wind up “threading” the rotor like a phonograph record. A feed rate that’s too slow can also cause problems. For instance, too slow a crossfeed can result in a rubbing of the surface, resulting in an unsatisfactory finish.
Q. How do we best prep rotors for installation on the car?
A. If you’ve refinished rotors, ensure a non-directional finish with #120 to #150 emery cloth/sandpaper or use a hone specifically designed for this purpose. When finished, wash the rotors with mild soap and water. Prior to installation, ensure that the rotor-to-hub mounting surfaces are clean and rust free. Use a wire brush or small angle grinder as needed until these surfaces are pristine. Failing to do this last, but critical, step can result in rotor runout and a comeback.
Q. We have an ongoing debate in our shop about the replacement of brake fluid. Some of our techs believe fluid ought to be replaced whenever it starts to look dirty. Other techs believe the fluid should only be replaced during brake work. What's the best policy?
A. For starters, it all comes back to the manufacturer's recommendations. Some manufacturers are more outspoken on this maintenance topic than others. Some may require a complete fluid change every two years while others may not say much at all. To help eliminate the guesswork, you may want to consider one of the brake fluid testers on the market. For example, brake fluid test strips indicate fluid condition by dipping them into the fluid and then comparing the color on the strip to a condition chart. There are also electronic testers that you can use to probe the fluid and take fluid condition readings. Remember, make sure to replace fluid with the proper type; use DOT3 or DOT4 as recommended.
Q. What's the best method of cleaning off brake parts during inspection and service?
A. Nowadays, a brake washer using aqueous-based solvent is the best way to go to reduce exposure to brake dust. Unlike the old days, where air pressure sent brake dust everywhere, a brake washer takes the residue away safely and effectively. Brake washers come in a variety of sizes, ranging from large units intended for production work, all the way down to small, portable units. No matter which unit you choose, make the proper use of a brake washer an integral part of brake service.
Q. We’re unsure about the procedure for checking rotors. Some of my guys believe that all you need to do is inspect the rotor surface for excessive rust, gouges and other surface problems. Is there a more conclusive way to do this?