Replacing rear brake rotor for highlander

Hi, I just have my rear brake rotor replaced with brake pad yesterday. But I found mechanics machined the disc to 0.335" thickness which is the minimum thickness according to Spec (the standard thickness is 0.394"). I just wonder if this is normal procedure to machine a new rotor to minimum specified thickness. If that’s true, does that mean I have to change rotor again when replacing pad next time, because mechanics will not turned the rotor below the minimum thickness.

Thanks for your opinion

You should not use brake discs (rotors) with thickness below the minimum. When they get too thin, they will tend to overheat, causing warping

I do my own brakes, and buy new rotors on every third pad change. They’re cheap enough ($13.00 each for Bendix rotors for my old Toyota Celica). So I don’t bother having them turned (I don’t have the equipment/skills for that).

I can’t answer the first part of your question (normal to machine down to minimum thickness). Did the shop tech suggest that you get rotors replaced?

I suspect the shop either replaced the rotors or machined the old ones, but did not machine new ones. How do you know the rotors were machined?

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Whether it is “normal” might not be relevant.
Consider it this way: before machining the rotor, the options were to

  1. reuse it without machining
  2. machine it before reusing IF there is enough material left on the rotor after machining that it still has minimum thickness.
  3. install new rotor.
    The cost factor between #2 and #3 may or may not have been significant to you.
    These same three options will be present the next time you need brake pads/rotor work.

Next, maybe consider that both the rotor and brake pads are ‘sacrificial’ items – IOW, they are worn down as part of the braking process. Yet some pads are ‘easier’ on rotors than other pads, such that a rotor wears down very little compared to the pad.
So the next time you need brake pads/rotor work, if the rotor has less than minimum thickness, then you will need new rotors (with no machining).

One should never machine a new rotor. If that’s what they did I’d ask for replacements.


I actually have a colleague who machined every new rotor before installing it

He claimed “the finish wasn’t smooth enough” . . . yet these were factory rotors

But by the time he was done, he’d probably cut the rotor’s useful life in half

After a few times of observing this, the supervisor gave the guy a verbal warning, and said if he caught him doing it again, he’d be written up

Was he machining motor pool rotors? Your coworker certainly should be written up for wasting the public’s money. If he was turning his own rotors with “company” equipment, he should be written up too, of course.

Yes . . . he was machining brand new Ford Motorcraft rotors

He stopped doing that, after the supervisor gave him a verbal warning

And I agree that he was wasting the public’s money

Those same rotors . . . the ones that he claimed had a rough finish . . . I always installed them without machining them, and I never had a problem

Makes no sense and is not the current normal procedure for brake jobs. Here is why (from our partner site).

Well, if You are pretty darned quick, You can get by without new pads as this (ahemmm) mechanic owes You a new disc - or set of disc’s - at no cost NOW - not tomorrow. As I see it.
If he has machined the disc(s) to minimun thickness, they are “worn” out and has to be changed as they will only get thinner from now on. A situation like this should not be possible - but…

It is not my practice to have new rotors turned, but I have noticed when buying Napa rotors a piece of paper is packed with them claiming all new rotors should be machined. I asked the counterman why they didn’t turn the new rotors before they gave them to me.

He shrugged his shoulders and said “I don’t know, it’s probably a lawyer thing.”

Did you measure the new rotors yourself or is this something you read on the invoice?

I suspect the report states that the old rotors were at .335" or less, that is the reason for new rotors.

It would take 5 to 6 cuts/20 minutes to cut a new rotor down to minimum thickness, that is too time consuming even for someone who doesn’t know what they are doing.