Before rubber can hit the road, those wheels need something to attach to. Brake lathes allow techs to properly care for a customer’s rotors or drums, help prevent uneven wear of pads and keep a vehicle stopping smoothly.
According to Greg Meyer, product manager of brake lathes and wheel balancers for Hunter Engineering, brake lathes have two purposes: to reduce lateral runout (seen when a wheel wobbles or shimmies), and to prevent variation thickness.
“The thickness variation is of the most immediate concern, because if you think about the brake pads that are clamping (the rotor) like a vice on both sides. If that rotor gets thicker as it’s passing through that, essentially that will increase the braking force. As the rotor starts to get thinner, suddenly you’re going to be not braking as hard as you were,” explained Meyer. “That will cause that pedal pulsation, a vibration, as you were braking.
“Think about that vise clamp that’s grabbing those rotors. That vise clamp is getting knocked back and forth. It’s going to get pushed from the left to the right, which is fine … but what that’s doing is causing uneven wear, that will eventually lead to a thickness variation, which would get you back to your pedal pulsation again. It’s today’s problem versus tomorrow’s problem,” said Meyer.
The first step to providing the right equipment is determining what kind of brake lathe is right for the shop.
ON-CAR VS. BENCH LATHES
There are two main types of brake lathes: on-car and bench. The difference is where the action takes place.
“On the bench lathes you’re removing the rotor, and then you’re taking that rotor and … using an arbor to clamp it up to the bench lathe,” said Meyer. “In the on-car lathe, you’re bringing the machine to the vehicle, so you don’t have to remove the rotors from the vehicle.”
Using bench lathes can be more time-consuming, not only with initial prep, but also the number of cuts to the rotor.
“In bench lathes, generally they will recommend a rough cut and then the clean cut, and then a finished pass. You can also do a single cut as well on a bench lathe, but the chatter control is more of an issue on bench lathes than it is on the on-car lathes,” said Meyer. (Additional accessories are available to eliminate that concern.)
You’ll find on-car lathes more often at larger shops and dealerships, not just because they’re faster and more efficient, but because many manufacturers require on-car lathes for warranty purposes. Because the wheel and rotor never leave the actual vehicle, techs have less room for error when cutting.
Meyer explains the concern with bench lathes:
“When you pull a rotor off of the vehicle, you may have turned it perfectly off the vehicle and then you install it back on the vehicle. Because it wasn’t installed the same way, you could unknowingly induce run out. You will, in essence, have undone some of your efforts.”
Although on-car lathes seem like the sure-fire bet for shops, some applications require a bench lathe, including at heavy-duty shops.
Also, any type of drum brake work needs to be done off the car. Meyer explains two reasons why.
“One is the design. That’s actually enough of a reason in and of itself. There’s no way to get inside around that drum because it’s a sealed unit. Whereas discs are open, essentially they’re exposed,” he said. “Also, the drum brakes are much less sensitive to run out than disc brakes are.”
Trends show that shops continue to work on disc brakes much more often than drum brakes.
“Basically, drum (brakes) are only used on the rear of some vehicles now. They’re never used on the fronts anymore; and 75 percent or better of your stopping power is at the front of your vehicle,” said Geoff Womer, product manager for Pro-Cut International. “Most of your brake jobs… almost two-to-one will be front brake jobs. Since all front brakes are rotors, they’re mostly going to be disc brake jobs.