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Brake Pads and Rotors

Re car talk Sunday July 20: I was interested about the lady who had brakes replaced and rotors turned which subsequently were noisy. For years I have replaced brake pads as it is a quite simple procedure, far removed from the hassle of replacing shoes in drum brakes. The last time I replaced pads on my now defunct 1992 Subaru, the Subaru dealer said, be sure to get the rotors turned otherwise the ABS will get confused. My engineering mind saw no logic in that so I did not get the rotors turned. Why would ABS get confused with new pads when it worked fine with the old pads?

Now when you get a brake job they require the rotors to be turned which I think is totally booooogus as you guys would say.

Interestingly, when my 1992 Subaru was new, I noticed a slight pulsating on the pedal when braking, but it went away after about 1000 miles.

I think one would have to be very abusive on the brakes to cause any warping of the rotors.

For the record, I am a Subaru addict. A Japanese car made in America and with zero pollution, what could be better. I recently had a passenger in my car who drives a Jaguar and who made the quite unsolicited comment, ?This is a nice car?.


I too am a Sooby addict. I bought my first in 1992 - a 1979 1600dl 4x4 wagon. Odometer didn’t work, drove it for 10 years, bought a 2003 Baja and just traded that off last fall for a B9 Tribeca LTD.

One think that ppl should keep in mind is to make sure their lug nuts are properly torqued, as imporper tightening can lead to warped rotors as well, regardless of driving (braking) style.

You’re looking at it from the perspective of a customer. A shop will look at it in a different light; and that is doing the job properly.
Properly means that rotors are always machined or replaced - period. Not only is the safe and proper way of performing a brake job, and it’s the approven method according to car makers, automobile organizations, etc., but it prevents “problems” from occurring. Problems means cutting corners on a brake job and the customer turning right around the next day/week/month/or even year, and blaming the shop for squeaking, vibrations, groaning, etc.

Replacing the pads only is an acceptable method for the backyard DIYer but it is not acceptable elsewhere. If you were actually a tech and having to stand behind your work then you would not be corner cutting.

Speaking as a formerly certified Subaru Master Tech (no longer work for dealers) I can tell you that rotor warping is as common as the morning sunrise; and Subaru has been one of the worst offenders.
Also, I was not aware that Subaru produced zero pollution. What model Subaru do you have?

For safety and reliability it is best to turn or replace the rotors.  On many (most?) newer cars the rotors and not designed to be turned, but they also happen to be cheaper to replace.  

Today new pads means new rotors for me, and yes I practice what I preach .

In response to your question; No, the ABS does not know or care whether the rotors have been machined or replaced.

Was the pulsing you felt for the first 1000 miles in the pedal or in the car? If it was in the pedal, I am surprised that it went away. If it was in the car, it must have been a bad spot in the rotor finish or a pretty nasty rust spot if it lasted that long.

All the rotors that I have dealt with in the past 20 years had so little tolerance between original thickness and minimum allowable thickness that machining them is not an option. If your rotors have enough ‘meat’ to allow machining them, do it only if you need to remove the lip from the inner and outer edges of the working area, and to true up and refinish the working area. If the rotor has metalurgical irregularities that cause it to warp, or if it has hard spots, machining it is pointless, at best a temporary fix.

DIYers can and often do run their rotors through several sets of pads with no machining or replacement with no problems at all. The only difference they perceive is the weight of their wallets. You just have to watch that the new pads fit in the old groove, and not run the rotors too far past the minimum allowable thickness, lest they start to loose heat dissipation capacity.

Back in the 1970s, Subarus had some serious design and fabrication problems. Many of them never saw 100k miles. In the past 20 years, however, I have not met anyone who regretted buying a Subaruu.

“I was not aware that Subaru produced zero pollution. What model Subaru do you have?”

I believe the reference is to the factory…ad on TV showing factory adjacent to a wildlife preserve.