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Rotor thickness specs

I was recently in an argument with a customer about this and was hoping for a little clarification.

My understanding is that it is prohibited by law(according to my brake spec book) to machine a rotor under manufacturers specs and return it to service. My questions is: Is it also prohibited to just pad slap a rotor that is already under specs? I understand it is a liability, but I’m just wondering the legality of it.

Also, if you could provide references to any pertinent materials, I would appreciate it. I was also in an argument with my DM about it and it would help to have something solid to back up my story.


Rotor thickness is a manufacturer spec, no government input exists as to the thickness of a rotor.

Where I live we have no safety inspections, but if there are where you live there MAY be a state regulation that prohibits issuing a safety certificate if a car is found to have undersized rotors. But that would depend on your locale and if a rotor/drum measurement is even included in the inspection.

Installing too-thin rotors is illegal in MA:

But it doesn’t say anything about just putting pads on.

Thank you very much Texases, That is pretty much EXACTLY what i was looking for!
But I’m still digging around to find out about just throwing pads on. Maybe I’ll write the MA legislature, I should probably get an answer by 2020 haha.

I cant find anything about saftey inspections in MA about rotor thickness, but i know in NH they have to be in spec to pass(i work in MA but i have my inspection license in NH and ME) which i assume would make it illegal to just pad slap a rotor under spec in NH.

If the rotor thickness is below specs then common sense dictates that you just don’t “slap a rotor” with new pads. I don’t know of any competent mechanics who would do that…myself included. The results could be catastrophic if it was done.

When a customer disputes your claim just SHOW them the specs cast into the rotor and show them the caliper measurment you get. let them watch you zero out your caliper and measure the thinnest groove.
If they insist on off spec repair make them sign a waiver.

Massachusetts has been passing laws for almost 400 years and by now, almost EVERYTHING is illegal…Most certainly, everything that’s FUN is illegal or prohibited…Thank goodness, 95% of these laws are never enforced…It’s the THREAT of enforcement that keeps people in line…

@ken That is exactly what my manager made the customer do. 98 blazer, rear rotors measured .714, discard is .728, and they were covered in rust pits, pads were fine, maybe 6/32" I was instructed to just replace the pads. “Just slap it and get paid”, i refused the job.

@misslieman You’re absolutely right, common sense and good work ethics dictate rotor replacement, but some management cannot be reasoned with.

Your shop should check with a lawyer to make sure the waiver, as written, is enough. Just takes one bad lawsuit…

If it was my shop I’d make it SOP to measure the rotors, requre replacement if they’re too thin. I’d bet there’s more money to be gained replacing too-thin rotors than would be lost on the few customers that wouldn’t spend the money to replace. And I’d sleep better.

I think you did the right thing. The customer and your manager may want the cheap, backyard way out but with one hiccup immediately afterwards or 6 months later they will both be your back.
A large number of those customers who are perfectly agreeable to a halfaxx fix will also be the first ones to come back cursing you or you will never see them again because they’re devoting their energy to cursing you all over town.

A comment about that .060 mentioned in the statute. That’s a lot of meat as most rotors and drums respectively have about .030 or .050 maximum that can be machined off.
The way that statute is worded a shop could machine and install rotors or drums that are way under spec, unsafe, and still meet the letter of the law.