Brake rotor minimum thickness?

[Charlie207]

Where would I find the specs for minimum rotor thickness (Front/rear)? My pads are getting low up front (rears still look fine), but I figured I don't need new rotors this time.

I found this info in the 2000-2006 section when searching for the GMT900 info, but I'm not sure if this applies:

Front JC3,JC4,JH2 nominal 1.142 discard 1.083
Rear JC3,JC4,JH2 nominal 1.181 discard 1.122
Front JH6 nominal 1.496 discard 1.437
Rear JH6 nominal 1.142 discard 1.083

 

[Fless]

Minimum thickness should be stamped onto your existing rotors. Might need some cleaning to read it.

 

[OR VietVet]

Rotors used to be thick enough that machining them at least once was ok. To get better fuel mileage numbers, the manufacturer has now put rotors on that are thinner and therefore less weight. Rotors will warp from heat during normal brake action. By the time you machine them flat and dress up the rotor surfaces, they are close enough to thin or are too thin and when they warp again, it will be more severe because the less thickness, the more likely to warp and then you will feel brake pulsation and wish you would have just replaced with the pads. Plus, the cost to machine them is not cheap and that money could go toward the cost of a new rotor.

In the business, we called them "Bic" rotors because we used them once and threw them away.

 

[B-train]

Agreed with @OR VietVet on this point. I wouldn't even consider reusing rotors these days, especially in salt states. I had thought of it on my 2017 that came from a rust free state. But after 4 winters here, the insides of the rotors were getting rusty. The face and fins looked good, but not worth monkeying with in my book.

Do yourself a favor and buy new rotors that have a good electrostatic coating to prevent corrosion. Clean the hub face nice and smooth - free from hight spots of rust, etc. Coat with anti-seeze and install new. You will appreciate the extra effort when the time comes to disassemble for any reason.

 

[Charlie207]

Minimum thickness should be stamped onto your existing rotors. Might need some cleaning to read it.

I'm lazy, and didn't want to pull two wheels off (again) to see the specs, and luckily RockAuto includes the info for the rotors I bought:

FRONT

Discard Thickness (IN)	1.102
Discard Thickness (MM)	28.000

REAR

Discard Thickness (IN)	0.728
Discard Thickness (MM)	18.500

I'll see if I can reach some calipers through my spokes and get a measurement.

 

[OR VietVet]

Do you know how much machining the rotors will cost compared to new ones?

 

[Charlie207]

Fronts are at 1.179" and 1.180"

Rears are 0.882" and 0.883"

If all I need to do is order pads, then I'd rather just do that. There's no shimmying under hard braking currently.

 

[OR VietVet]

Fronts are at 1.179" and 1.180"

Rears are 0.882" and 0.883"

If all I need to do is order pads, then I'd rather just do that. There's no shimmying under hard braking currently.

Guess what, it is your vehicle and you get to do what you want to. Bear in mind that the old rotors also are seated in to the old pads. That old rotor surface will not seat in as easily as with new rotors. If you insist on using the old rotors, then do yourself a favor and remove the rotors, clean then thoroughly with brake clean and do a scuffing resurface of the rotors and after that, use brake clean again. If you have debris and small metal flakes on the rotor surfaces, that will imbed in the pad surface when you apply the brakes. Even with new rotors, the surfaces should be cleaned with brake clean before usage. The scuffing of the old rotor surfaces helps allow the new pads to seat in to the old rotor surface. There is always a higher % chance of brake squeal from using old rotors. Cleaning and lubing the caliper guides is a must and so is using new pad hardware.

It sounds like you have decided not to even resurface the old rotors. I absolutely guarantee you, those old rotor surfaces are warped.

 

[Charlie207]

I absolutely guarantee you, those old rotor surfaces are warped.

I'm not picking sides, but I've seen some arguments that rotors don't warp, and it's more of a surfact build-up issue. Proper brake pad bedding is able to eliminate the pulsing feeling that people associate with "warp".

That's what I've heard, anyways... and they were very passionate about it.

There's some support it: https://www.motortrend.com/how-to/1808-nuts-and-bolts-warped-rotor-myth/

Warped Rotors - Service Brakes: Runout, Disc Thickness

Related Articles - Tesla Wheel Bearing Replacement - Tapered Wheel Bearings - Brake Pad Ecology Myths take hold because either A) they seem completely logical or B) they are so often repeated that they just become common knowledge. The warped rotor myth is a little bit of both. A rotor that...

www.brakeandfrontend.com

Solved: The Mystery of Warped Brake Rotors

trade.mechanic.com.au

 

[OR VietVet]

I have machined literally thousands of rotors in my shops over the years. Each and every time that I put a used rotor on a brake lathe, it was warped to some degree. Every time. Yes, you can have some build up on the rotor surface, especially in salt road states. The major runout though was heat related rotor warpage.

Apply brakes, pads rub rotors, heat is built up and temps climb, heat transfers into the metal rotor and over time, that rotor will warp. Depending on design and initial thickness, that warpage will be more or less on certain rotors. You will not feel that warpage when it is under a certain measurable amount but once it reaches a higher amount, you will feel it. I have even seen new rotors that were not true.

Is there a possibility of newer rotor substances that don't warp like they used to, sure, but I guess i am too old school to be aware of them and I will look at your links.