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Reuse brake rotors versus resurface or replace?

Can you reuse brake rotors or should you have them resurfaced or replaced?

Brake rotors don’t last forever so you and the technician must make a decision whether to reuse brake rotors versus resurfacing or replacing them. As car makers have reduced the weight of their vehicles to gain fuel economy they’ve reduced the thickness (and weight) of the brake rotors. In the old days a technician could easily resurface a brake rotor twice. Today, some rotors are so thin right out of the factory that a single resurfacing procedure can thin them to the point where they no longer meet the factory “discard thickness.”

Brake rotors can look perfectly fine to the naked eye, making you think you can reuse brake rotors. But looks are irrelevant—brake rotors must be measured with a brake micrometer to determine whether they can be reused or resurfaced. Here’s what the technician must measure before making the decision are the pros and cons for each of those decisions. Once the measurements are taken, consider the overall condition of the rotor and costs of resurfacing versus new.

What to measure before you decide whether to resurface a brake rotor
Measure rotor thickness

The legal minimum thickness is stamped into the rotor. So the technician  must measure brake rotor thicknessuse a brake micrometer to measure the rotor’s current thickness. In order to be a candidate for resurfacing, the rotor must exceed discard thickness by at least 0.015-in. That’s called “machine to”  thickness (discard thickness plus 0.015-in.). The machine to thickness is calculated to leave enough metal on the rotor after resurfacing to allow for brake rotor discard thicknessenough rotor wear following the resurfacing to ensure the rotor does not fall below discard thickness during the life of the new brake pads. If the rotor measures at or above machine to thickness, then it might be a candidate for resurfacing, but only if it passes these other tests. If the rotor doesn’t meet that thickness it must be discarded.

Measure brake rotor groove depth

Brake rotors are exposed to road dirt and grit and that grit can become trapped between the brake pad and rotor, causing the grit to wear grooves into the face of the rotor.  A rotor with minor scoring can be reused as is. scored rotorHowever, if the groove depth reaches 0.060-in. it must be resurfaced or replaced. To be a candidate for resurfacing, the technician must calculate how much rotor material must be removed to level the rotor face and remove the grooves, while still meeting the machine to thickness. If the rotor won’t be thick enough after resurfacing, it must be replaced.

Measure disc thickness variation and parallelism

disc thickness variationImproper lug nut tightening, sloppy brake installation, road impacts and rust buildup can cause a rotor to develop thickness variations and parallelism problems. If a rotor has these issues, the technician must  calculate whether there will be enough remaining thickness to justify resurfacing.

If the technician makes all these measurements and determines the rotor will have enough metal remaining after resurfacing to meet the machine to specification, then you can consider resurfacing as long as the shop uses an “on-car” brake lathe.

 

Consider the condition of the rotors

clean brake rotorRotors rust and some of that rust can greatly rusted rotor finsaffect the rotor’s ability to dissipate heat.  The most critical areas are inside the cooling fins and the mating area where the rotor meets the  wheel hub. If the cooling fins are clogged with rust scale, it must be removed and that can be labor intensive to the point of making it uneconomical.

Consider the costs of resurfacing versus replacement

The labor required to resurface a brake rotor using an on-car brake lathe can often cost more than a brand new brake rotor. Resurfacing a rotor takes three separate steps: rough cut, fine cut, machine rotorsnon-directional finish application. It takes about 30- mins per rotor to install the on-car brake lathe and perform the resurfacing procedure. If the shop charges $100/hr. and brand new rotors cost $50 each (2 required per brake job), you’re better off replacing the rotors as long as the shop will be using professional grade name brand rotors. See this article on brake rotors

 

©, 2016 Rick Muscoplat

 

 

Posted on by Rick Muscoplat

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