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The result was that the only significant detrimental effect was noise, period. Using both drums and rotors taken off of real life vehicles and drums and rotors that had grooves machined in them, we found no degradation in brake torque output (both immediately after the new linings/pads were installed and when fully broken-in), a slight (<10%) increase in wear rate and actually a faster rate of lining/pad break-in (i.e., the number of miles before the brake torque output completely stabilized) with the “grooved” vs. the “new or resurfaced” drums and rotors. However, they could be noisy. Notice that I said “could be”, because they did not always start out noisy and the noise tended to come and go. We theorized, but never proved, that the intermittent noise was caused when a “new” part of the lining/pad just began to come in contact with the drum/rotor and until it was in full/firm contact with the drum/rotor it would squeal. My “personal” (definitely not the agency’s) theory for the brake repair industry’s obsession with resurfacing brakes is:
Since knowing the results of this research, I have never resurfaced the brake rotors on any of my Alfas. Since ’71, I estimate that I have driven Alfas (and by the way, except for rental cars, only Alfas) about 350,000 miles and probably changed brake pads (counting front and rears separately) more than 40 times, and the only times that I’ve ever replaced rotors was when they were worn below the minimum spec and when I put cross-drilled Shankle rotors on one of my Milanos. Twice with Alfetta Sport Sedans and once with one of my Milano, I have worn pads down to the medal, put grooves more than an 1/8 of an inch deep in the rotor and simply changed the pads. In one case with an Alfetta, after about 1200 miles I took the car to a demonstration that the Hunter company (alignment and brake test equipment) gave for NHTSA personnel (by the way, we were encouraged to bring our personal vehicles to use for the demo) of a new brake test dyno. The result of the test was that the variation left to right between a “good” rotor that only had about 13,000 miles of use and was on its second set of pads and the rotor that had the 1/8 inch grooves was 4%.
The problem with what I am recommending is that virtually all shops “will not give you a warranty on the brake job” if you don’t let them resurface the brakes. So for all you D-I-Y’s out there, you can save yourself some expense, that is if your hearing is as bad as mine - What did you say??
—Scott Shadle
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Please keep in mind also, that I am looking at this from the viewpoint of the “professional” mechanic. If doing this yourself and it works for you than this is fine. However, as a “professional” I cannot afford to have customers coming back due to any or all of these symptoms, plus I hate to say it, but there is also the issue of liability, so in my case it is better to take any and all of the precautions rather than risk having an irate customer come back due to squealing brakes which I will then have repair a second time at no cost to the customer and I will probably lose them as a customer after this ordeal. By the way I never just replace the brake pads in any of my cars either—I always resurface the rotors first.
—Jeff Greenfield