turning rotors

Donald · Jun 30, 2012

In the past people have commented that no one turns rotors as a turned rotor is more likely to warp because its got less metal. Makes sense.

But most rotors are not warped but are not of uniform thickness and have pad deposits welded to the rotor surface.

Once the rotor is turned the pad deposits are gone, hopefully the rotor is still usable with respect to minimum thickness.

Now the turned rotor weighs slightly less, less metal, thinner and will heat up faster. But percentage wise with respect to thickness and weight, I am guessing its less than 5% from new. A rotor going to the scrap pile is still heavy.

Also given the low cost of rotors, in many cases its cheaper to throw on new rotors made in China than pay a US mechanic to turn them. Sending them out ties up the lift, etc.

But for a shade tree mechanic things are different. He can try and have the rotors turned, in most cases not in a rush, no lift to tie up.

Maybe a nagging wife asking when the brakes will be fixed.

simple_gifts · Jun 30, 2012

Too timely, I just PM'ed a fellower BITOG'r indicating turning rotors is just not cost effective when a new Beck Arnley is $30 for my vehicle.

My worry is having someone who knows anything turn them. Of course, now I have my new BA's the old ones are sitting on my porch waiting for "something" to be done with them.

LeakySeals · Jun 30, 2012

I've been wondering that too. But I don't read anyone turning replacement rotors either anymore. The good brands can be had at www.rockauto.com cheap.

Hokiefyd · Jun 30, 2012

Rotors for my vehicles run in the $50-60 range for good ones. It costs me $10 for an old-timey independent garage to turn them. I personally have had great results with having rotors refinished.

Eddie · Jun 30, 2012

Much depends on the person doing the turning and the condition of the rotor. I have no issues nor have I had any problems with turned rotors where ~ 0.010-0.020 is the amount taken off or considered a cleanup cut. Ed

wirelessF · Jun 30, 2012

I spent $40 to get my Brembo slotted rotors machined to get rid of a pulsating feeling when braking. I bought them $250 several years ago new and try to get the most life from them. The rotors slots also serve as a wear indicator when to replace the rotor. Since there's a lot of life yet I'll use them until the next brake job.

I try to get rotors replaced/shaved when changing brake pads. Apparently I just took an emery cloth to the rotors when I just installed the new pads and upgraded the calipers. Old pad bed-in material didn't get removed and probably the new pad material just built over it that caused "warped brakes".

Donald · Jun 30, 2012

Originally Posted By: LeakySeals
I've been wondering that too. But I don't read anyone turning replacement rotors either anymore. The good brands can be had at www.rockauto.com cheap.

Shipping is the killer for rotors. Amazon is free in many cases.

Chris142 · Jun 30, 2012

I have turned many rotors in my time. I can only remember a couple cars that had brake pad material built up on them which caused a shake when braking.

The rest, Probly hundreds were visibly warped. They did not have an uneven surface, They measured the same thickness regardless of where you measured them. Once on the lathe and spinning I could see the wobble and once cutting them 1/2 of the rotor per side was getting cut.

As I have stated in the past. Warped rotors are much more common than uneven rotor thickness from pad material.

stephen9666 · Jun 30, 2012

I went through this recently.

Turning the rotors on my Sonata would have been around $15 -17 each at the local parts stores. New Raybestos rotors were $27 each shipped.

It was not worth it to me to turn them. The OE rotors had a lot of wear and tons of rust in the vanes. It was an easy choice for me, but that may not be the case for every application.

artificialist · Jul 1, 2012

Some cars leave the factory with rotors that warp too easy, so machining them flat is pointless, and buying new premium rotors is the only solution to warping.

HerrStig · Jul 1, 2012

YOu buy a rotor lathe on "time" you turn a LOT of rotors with it. Simple.

mechtech2 · Jul 1, 2012

It's a matter of cost nowadays.
Rotor cutting used to be reasonable, and now it it very high, with luck being a huge factor in the final finish and trueness.
Uneven metallurgy, internal rusting , warping, out of round, and dirty mounting surfaces cause brake pulsation.

BTW, I think the 'shade tree' mechanic is in more of a rush to get his car back together as soon as possible.
Why would cutting them be less time than ordering them and having them delivered in a shop?? It may very well take longer.

For street use, brake pad deposition is normally a non issue. The material is worn off faster than it is deposited. Racing and HARD use like in the Stoptech articles is way different, and they say so.

ArrestMeRedZ · Jul 1, 2012

Originally Posted By: artificialist
Some cars leave the factory with rotors that warp too easy, so machining them flat is pointless, and buying new premium rotors is the only solution to warping.

+1.

The 98-02 GM F-bodies were notorious for this problem. My factory rotors warped in less than 10k miles. I didn't bother to get a warranty fix, as the GM TSB only allowed the dealer to machine them. My solution was to install cryo treated Brembo blanks.

Now that most rotors are Chinese junk, you are going to see more of this. Chinese factory managers will slip in sub-standard iron/steel whenever they aren't being watched.

tightwad · Jul 1, 2012

Originally Posted By: Chris142
I have turned many rotors in my time. I can only remember a couple cars that had brake pad material built up on them which caused a shake when braking.

The rest, Probly hundreds were visibly warped. They did not have an uneven surface, They measured the same thickness regardless of where you measured them. Once on the lathe and spinning I could see the wobble and once cutting them 1/2 of the rotor per side was getting cut.

As I have stated in the past. Warped rotors are much more common than uneven rotor thickness from pad material.

Very true. I spent many years in auto parts stores turning rotors.
Some were warped from overheating, but many only started to pulsate after having the tires rotated. Yeah, good ol' Goober and his air wrench.
I always turn my old rotors when doing a brake job. The secret is to polish the surface with a sanding disc on a drill to remove the groove left from the bit. Also sanding the mounting surfaces before mounting to the lathe and re-checking the mount-up is important. I've even checked and turned new ones to get them perfect.

mechanicx · Jul 2, 2012

I agree with your assessment. OEMs have proven in their research that pulsation is usually caused by rotor thickness variation from uneven wear off braking caused by rotor lateral runout. And not so much from overheated rotors that warped or from uneven pad deposits.

A warped rotor is different from run out and is a curvature or lack of flatness. Although it's not impossible for a rotor to warp and it can also lead to uneven wear and thickness variation. A wobble seen on a rotor on a brake lathe is likely run out. Disk thickness variation can cause pulsation at levels of less than 0.001 and even at 0.0008 or less. So it's very hard if not impossible to measure for.

So if someone has pulsation and their rotors are turned off the car, and a few thousand miles later the pulsation returns, it's easy to attribute it to warped rotors that ran too hot from removal of metal.

But what is typically happening, assuming the rotor was turned true and within minimum thickness, is the rotor is mounted on a separate wheel hub that is inducing rotor run out. If the brake rotor was turned on the car, or if run out was checked and the rotor was indexed or shimmed etc and run out was within specs, the pulsation likely wouldn't return.

But here's the thing. Installing new rotors won't permanently correct that problem either. Hub run out will lead to thickness variation and pulsation with the new rotors too.

Now if some installed different new pads and rotors to correct pulsation and the fix held, that points to a rotor problem but doesn't necessarily disprove run out was the original problem and it was warped rotors. It's possible reindexing the rotors reduced run out and also different pad types like semi metallics seem tolerate more thickness variation and wear the rotor high spots down while on braking.

You can weigh the cost of replacement vs turning rotors, but if it's the OE rotors it's not really a fair comparison to compare turning vs the price of a chinese rotor special. Even some of those can run close to $50 for some applications.

You do have to consider how bad of shape the rotors are, cost of turning vs replacement and whether the turned rotors will have a good finish and run out is eliminated. But I don't think turned rotors warping is really a concern.

Hokiefyd · Jul 2, 2012

This is why on-car brake lathes are becoming more commonplace. Admittedly, I had to search around a fair bit to find somebody would turn turn my carry-in brake rotors this past Saturday.

Vikas · Jul 2, 2012

What do you do with the old rotors if you don't happen to own a boat? There is no core on them, right??

Hokiefyd · Jul 2, 2012

Correct. Trash-ola. Or recycling if they take scrap metal (most do these days).

Donald · Jul 2, 2012

Originally Posted By: mechanicx
I agree with your assessment. OEMs have proven in their research that pulsation is usually caused by rotor thickness variation from uneven wear off braking caused by rotor lateral runout. And not so much from overheated rotors that warped or from uneven pad deposits.

A warped rotor is different from run out and is a curvature or lack of flatness. Although it's not impossible for a rotor to warp and it can also lead to uneven wear and thickness variation. A wobble seen on a rotor on a brake lathe is likely run out. Disk thickness variation can cause pulsation at levels of less than 0.001 and even at 0.0008 or less. So it's very hard if not impossible to measure for.

So if someone has pulsation and their rotors are turned off the car, and a few thousand miles later the pulsation returns, it's easy to attribute it to warped rotors that ran too hot from removal of metal.

But what is typically happening, assuming the rotor was turned true and within minimum thickness, is the rotor is mounted on a separate wheel hub that is inducing rotor run out. If the brake rotor was turned on the car, or if run out was checked and the rotor was indexed or shimmed etc and run out was within specs, the pulsation likely wouldn't return.

But here's the thing. Installing new rotors won't permanently correct that problem either. Hub run out will lead to thickness variation and pulsation with the new rotors too.

Now if some installed different new pads and rotors to correct pulsation and the fix held, that points to a rotor problem but doesn't necessarily disprove run out was the original problem and it was warped rotors. It's possible reindexing the rotors reduced run out and also different pad types like semi metallics seem tolerate more thickness variation and wear the rotor high spots down while on braking.

You can weigh the cost of replacement vs turning rotors, but if it's the OE rotors it's not really a fair comparison to compare turning vs the price of a chinese rotor special. Even some of those can run close to $50 for some applications.

You do have to consider how bad of shape the rotors are, cost of turning vs replacement and whether the turned rotors will have a good finish and run out is eliminated. But I don't think turned rotors warping is really a concern.

So what is the best route to head down. I just spent several hundred dollars for new calipers, pads, rotors (and for fun flex brake lines) to "convert" my failing Tevo calipers to Akebono as per the Jeep TSB. The pulsation is significantly reduced but not gone. The indy shop said it must be the rear brakes.

My plan is to order some Wagner TQ ceramic pads for the rear, pull the rotors and have them turned if possible. Wire brush the rust from the hub and rotor mating surfaces. If the rotors cannot be turned I will probably get some from Amazon. But the run out is a concern. How easy is it to measure?

mechanicx · Jul 2, 2012

It's not hard to measure run out but you need a dial indicator kit. There's a cheapie for $35 at Harbor Freight and others online starting at around $60. Once you've measured any run out, you still have to correct it either with reindexing the rotor, rotor correction plates or turning the rotors with an on-the-car brake lathe. Probably the easiest fix is to find a shop that can turn the rotors on the car.

turning rotors

Similar threads