Your Corner Wrench: Don't bother with machining your brake rotors

Nov 19, 2023

If a shop is trying to upsell you on machining brake rotors, find a way to politely decline

During seasonal inspections, a common recommendation from technicians of every stripe is routine brake maintenance. After all these critical safety systems are exposed to the worst of our roads and as most of the metal involved is untreated steel, the corrosion that accumulates can quickly reduce braking efficiency and performance. But one recent change has brought some doubts and questions from consumers wondering why no one machines or resurfaces brake rotors anymore instead of replacing them outright.

The first reason for this is design. Almost every passenger vehicle and light truck today uses brake rotors that are separate from the wheel hub and bearing. In the past, rotors (or discs) were incorporated into the bearing's hubs as one piece of machined steel. These units were heavy, with rotor thicknesses designed to be cut or thinned by a specialized lathe at least once or twice in their lifetime, the idea being to return the rotor faces to a clean, even, and rust-free surface permitting effective and quiet brake action In an effort to improve fuel economy and meet government regulations, automakers were happy to put their vehicles on diets, and separated brake rotors resulted in major weight savings

Today's rotors have very little room for machining as they are usually made so lean to begin with, and any loss of mass or thickness makes them prone to warping when they reach operating temperatures. The move away from asbestos in brake pad or lining construction also provides its own quirks; heavier metal and more ceramic content in pads can create a lot of glazing on the surface of the rotors. If this isn't removed when new linings are installed, it can cause a lot of squealing and can prevent the linings from properly wearing in.

Increased labour costs also added another nail in the rotor machining coffin. With quality rotors for many mass-produced passenger cars priced at less than $100 each, and shop labour rates increasing to match inflation and cost of living jumps, fees for machining rotors can run around the $60 to $80 each mark with new replacements costing very little more.

Sometimes, shops are a little aggressive in suggesting new rotors when the brake pads don't require replacing. If your ride isn't exhibiting any braking noise or vibration, simply pass on a brake rotor replacement if the pads are OK. Rust often forms first on the edges of brake rotors and this can cause noise, but it's also easily removed with little effort with some light taps of a hammer or some quick grinding with a buffing pad on a power-drill.

If you’re faced with the opposite situation — the rotors are shot, but the pads still have lots of life — resist the urge to go cheap and forgo the rotors. That shiny glazing on the rotors will make it almost impossible for the new pads to ‘seat’ or wear in correctly, leaving you with a lot of brake noise. And trying to sand off that glaze without creating an uneven surface is nigh onto impossible.

Brian Turner is still kicking and doing his best to put over 4 decades of frontline parts and service experience to work helping you understand not only how your vehicle works, but how to get the best deals when getting it repaired or maintained. He started with us at the Ottawa Citizen and hasn't looked back. He survived rooming with David Booth during his university days and we all admire him for that.

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