How necessary is rotor turning/re surfacing?

that’s true sarge…

“If the rotors have been damaged by the pads wearing out completely and it was steel against steel, then you replace the rotors”

I’m not saying anybody is wrong

In the shop, I’ve had vehicles come in where the driver ignored the screeching for a long time

In some cases, I was able to successfully machine the rotors, and they still had a lot left for wear. Nowhere close to discard thickness. Sometimes the rotors look far worse than they are

But if you don’t want to take chances, replace the rotors

that s kind of my point, why bother machining and removing more metal. just let the pads wear it down gradually. it does not take long for them to adjust and like an old married couple they eventually settle quite comfortably into each others imperfections

“like an old married couple they eventually settle quite comfortably into each others imperfections”

Sounds like my late maternal grandparents

My grandfather was kind of irresponsible, financially anyways. But he had a great sense of humour, and he always saw the humour in every situation, no matter how bad. One evening at dinner, one of his teeth came out. And he was the one who immediately started making jokes about it

My grandmother was financially savvy, and kept the whole operation running, so to speak. But she had absolutely no sense of humour. She was always busting my grandfather’s chops, for not being serious, for always joking around, etc.

But in the end, I think they wouldn’t have wanted it any other way

There’s also a huge difference between cutting corners on your own car as opposed to doing it for hire and being expected to stand behind the job.
Not servicing or replacing the rotors can lead to squeaks, shudders, or pulsations at any point after the job is completed and even lead to lawsuits.

Most rotors have about .030 of an inch to play with when it comes to surfacing and shaving .010 or even .020 off should not create any problems. Most clean up around .010 of an inch.

Some rotors (the ones on my Lincoln for instance) are pretty meaty and have about .060 or more to play around with before meeting the minimum thickness specification.

you are right db, this is my car i m talking about,and if I was a pro I would want to change such a rotor and would cover my butt

I remember machining 2mm . . . around 78 thousandths of an inch, I believe . . . off of a set of rotors some months back. It was for a fairly large truck

After I was done, it still wasn’t anywhere close to discard thickness

I think I’ve related this story before but for the benefit of those who haven’t heard it. About a dozen years ago I went into a local tire store one Sat. for some new rubber. This store also does brakes, shocks, etc.

While loitering around I noticed a brake rotor hanging from a peg behind the counter. When the manager came back in I asked him if someone actually came into the shop with brakes in that condition. He called me over to the south window and pointed out a long black tire mark from the lot which disappeared down the street.

This was a GM ventilated rotor in which the entire inner surface was completely gone and the outer surface was half gone and utterly wiped. The caliper piston had eaten its way through the rotor and wedged into the cooling fins which then locked the wheel.
The lady drove the car with a locked front wheel from 8 blocks away and just as she screeched onto the lot the tire blew out.

According to that lady the brakes were fine up to the point the wheel locked and there had been no grinding or noises of any sort. Right.
When told she was going to need everything on the front brakes she questioned whether or not “all of that stuff is really necessary”.

After I left the tire store and just for hoots I followed the black mark on the streets. It began in the 900 block west and ended at the 200 block west so the 8 blocks of skidding was no lie…

what? what ? brakes? no the the brakes are fine, it the wheel that stopped rolling. and stop mumbling sonny! I can t hardly hear you over that darn firebell that’s been ringing for the last couple years. they should have fixed that by now, don t you think? what? what?

i can say that because i m half deaf myself

Public transit is under rated.

Not only were rotors of old more robust than today’s rotors, but they worked with softer brake pads than we use now. The transition from asbestos brake pads to metallic and ceramic compounds has been the biggest reason for the change in rotor maintenance IMHO. Like the pads, rotors are now considered a wearable part.

Because I do most of my own brake work, I’ve gotten away with using a set of rotors over the lifespan of several sets of pads, but eventually, the rotors warp. At that point, I have a choice of machining the rotors or replacing them, and since thinner rotors warp easier, I usually opt just to replace them. Unfortunately, the last time I replaced my rotors, they warped within a matter of months, so I took them back in to have them machined. They haven’t warped again yet, but I know it’s just a matter of time. I’m thinking of using drilled rotors next time.

The drums on my car’s rear brakes are the originals, but even with plenty of pad left on the shoes, they’re getting noisy, so I’m thinking about replacing the shoes and drums next time I’m doing brake work.

I have to say that continuing to use rotors that have grooves in them left by the bolts on a worn out pad is something I’d never consider doing. Locking your brakes to stop is not going to give you the shortest stopping distance, even when you have good traction, so I don’t use that as a measure of whether the brakes are good. The way to get the shortest stopping distance is to apply the brakes to the point just before they lock. Locking the wheels in a panic stop is a mistake best avoided in any driving conditions, wet, dry, or frozen.

i never said that i locked them up in the emergency stop i mentioned. i did not.

i said that as long as you can lock brakes up you have plenty of force per square inch to spare, so the added friction of the increased surface area of the rippled pad and rotor was not too much for the caliper to handle. the truck was much easier to stop, especially when loaded as it often was since i had a cap on it and i kept my tools there .

completely different

i have the same year and model truck now, with the same caliper brand and size, albeit with flat rotors. it is harder to stop when loaded than the other truck was.

its real life experience. the first week or so it was harder to stop as there was not as much contact with the new pads. once they wore in though, they worked great. i was not the only one who noted this. an experienced mechanic did as well

There’s no question that ripples create more surface area and that more surface area can create the opportunity to achieve more friction, but in reality it isn’t that simple.

First of all, if you were to actually measure the additional surface area I doubt if it would be more than 1%. The ripples feel bigger than they actually are.

Additional factors in friction are the surface condition other than the ripples, the microscopic stuff like “finish” and glaze (if there’s any). That makes a huge difference. And then there’s the pad material itself. That makes a big difference.

The other thing to realize is that if the brakes are capable of locking the wheel, the only difference the ripples could make is in how much pedal pressure would be required to do so.

The question interests me on an intellectual level because the logic is there and actual testing might prove it makes a bigger difference than I envision. But theories always need to be tested to find out if they’re factual.

@wesw: “i never said that i locked them up in the emergency stop i mentioned.”

I’m relieved we don’t have to argue about what you said, because I never claimed you said that. I was using that example to demonstrate that being able to lock up your brakes isn’t a very good measure of their quality. I’m glad it worked out for you, but continuing to use a damaged rotor is something I would discourage for anyone I care about.

mountain. I respectfully dis agree. the increased surface area was much much more than one percent. these were serious grooves . try it with two pieces of string. I think you ll be surprised.

I am rather perceptive and I notice every subtle change in my vehicles, even if I don t know a lot about why, I notice everything that changes.

trust my actual experience on this. it helps significantly, especially when heavily loaded, when its more difficult to stop

You might be right. I wish I had a laser CMM or laser depth gage like a Lasercheck and a worn rotor to measure. Anybody out there up to the challenge?

as I would discourage removing more metal un necessarily, by turning the rotor to remove grooves.

if my rotor was warped, I would replace it

the increased surface area would also allow the rotor to release more heat theoretically.

I agree with you on the replacement practices. I too believe it’s better with rotors that are not warped, badly gouged, or glazed, to let new pads seat themselves to the rotors than to turn of replace the rotors. But if I owned a shop I’d replace them all, not for the extra money but to be sure the customers are happy.