is on car rotor cutting the best method?

Messages
1,330
Location
Washington for now
Thread starter
watched a few vids about on car rotor cutting machines. they tout that they do a better job as they compensate for total run out of the whole assembly. seems to be very important for FWD cars especially Hondas. So are these machines really the best for machining rotors? do they prevent or lessen the chance of pulsatiing pedal and wheel shake?
 
Messages
22,288
Location
CA
For most OEM's, machining a rotor on-car is the only method that is allowed for any warranty claims. It is possible to match the results of an on-car lathe if you use a bench lathe that is in great condition (with a knowledgeable operator), but these are far and few.
 

4WD

Messages
13,549
Location
Texas
Originally Posted by GMBoy
New rotors. Turning them isn't worth the hassle.
And in many cases you can upgrade to more corrosion resistant discs
 
Messages
14,449
Location
The Old North State
I've had rotors turned off the vehicle on Accord and Civic several times, never an issue. I do prefer using a shop that finishes with a non directional finish or post lathe surfacing over a directional finish. I had it done for brake pulsation and it did work. ymmv That said, I suppose if one is willing to pay the cost difference for having an on the car turning done, have at it. I'd buy new rotors before I'd do that.
 
Messages
4,848
Location
VA
I have never had good luck turning my rotors. Of course, I probably made bad choices in where I took my rotors to be turned. I only buy new OEM rotors and OEM pads now.
 
Messages
24,843
Location
Upstate NY
Many years ago some 4WD vehicles (Ford Ranger) had the rotor integrated into the hub and you had to take apart the entire hub to remove the rotor. In that case on-vehicle rotor machines were used. Today people just get new rotors.
 
Messages
468
Location
Newport News, VA
I have only ever bought a set of rotors and that was for ones that were rusted on. I had to cut and split them off with a chisel. I have even taken rotors off and ground them by hand on my concrete driveway to remove a edge ridge. None of the rotors out of some 10 cars have ever caused brake problems. I buy lifetime brake pads and DIY. They also don't shake, but I do have one Ford Contour that does shake a tiny bit, but they are not warped, they have some hard spots on the metal surface. I use rotors others would cringe at as they are not perfect and smooth and swear they must be ground and the car stops fine with new brake pads. Take that car into a mechanics shop and they will tell you new rotors or turn them. the car business will kill you with money costs unless you know what your about, and I have wrenched for 40 years and used to be a mechanic at a Chevy dealer, yeah we would make the customer buy all sorts of new stuff even if the original parts were still ok.
 
Messages
9,937
Location
Jupiter, Florida
It's good to know that if a rotor warps when hot, it's going to warp when hot after it's been turned. One thought is that the recycled metals are distributed unevenly in the disk. Another is uneven cooling, the metals in one location were "tempered" by a red-hot stop, then keeping the pads clamped on that location while the rest of the rotor slowly cools. Regardless of why it happens, "IF" you experience heat related warping, replace the rotor.
 
Messages
468
Location
Newport News, VA
Originally Posted by Cujet
It's good to know that if a rotor warps when hot, it's going to warp when hot after it's been turned. One thought is that the recycled metals are distributed unevenly in the disk. Another is uneven cooling, the metals in one location were "tempered" by a red-hot stop, then keeping the pads clamped on that location while the rest of the rotor slowly cools. Regardless of why it happens, "IF" you experience heat related warping, replace the rotor.
https://www.onallcylinders.com/2017/05/19/6-biggest-brake-rotor-myths-debunked/ Rotors do not warp. I am a mechanic. It is a myth. I did turn one badly once and since it was not true it pulsated and had to get re-turned. https://www.brakeandfrontend.com/warped-rotors-myth/ https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3043065/1 https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3895543/all/Brakes_Rotors_DON'T_WARP__-__A
 
Messages
3,240
Location
Ca.
Originally Posted by sdowney717
Originally Posted by Cujet
It's good to know that if a rotor warps when hot, it's going to warp when hot after it's been turned. One thought is that the recycled metals are distributed unevenly in the disk. Another is uneven cooling, the metals in one location were "tempered" by a red-hot stop, then keeping the pads clamped on that location while the rest of the rotor slowly cools. Regardless of why it happens, "IF" you experience heat related warping, replace the rotor.
https://www.onallcylinders.com/2017/05/19/6-biggest-brake-rotor-myths-debunked/ Rotors do not warp. I am a mechanic. It is a myth. I did turn one badly once and since it was not true it pulsated and had to get re-turned. https://www.brakeandfrontend.com/warped-rotors-myth/ https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3043065/1 https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3895543/all/Brakes_Rotors_DON'T_WARP__-__A
Thats what Ive found Rotors dont really warp, pad material imprints on them and causes the pedal to pulse and the wheel to shake. The phenomena is called non-uniform pad imprinting. Ive seen a hundred rotors on a lathe and have yet to see one thats warped. UD
 
Messages
2,401
Location
pa
today most rotors + even brand names are cast in CHINA + quality can vary a LOT. better rotors with better metallergy aka higher carbon content stop better + thats why i buy EBC branded rotors with casting + quality machining in the UK as well as USA for their pads.
 
Messages
14,479
Location
...
Originally Posted by benjy
today most rotors + even brand names are cast in CHINA + quality can vary a LOT. better rotors with better metallergy aka higher carbon content stop better + thats why i buy EBC branded rotors with casting + quality machining in the UK as well as USA for their pads.
What a bunch of malarkey.
 
Messages
22,288
Location
CA
Originally Posted by Sayjac
I've had rotors turned off the vehicle on Accord and Civic several times, never an issue. I do prefer using a shop that finishes with a non directional finish or post lathe surfacing over a directional finish. I had it done for brake pulsation and it did work. ymmv That said, I suppose if one is willing to pay the cost difference for having an on the car turning done, have at it. I'd buy new rotors before I'd do that.
I am mostly in agreement. In most situations, new rotors will be superior to the "average" rotor resurfacing that is performed using a bench lathe. However, keep in mind that some hubs and wheel bearings will have excessive runout and despite having a perfect rotor, the total runout of the assembly will exceed the manufacturer's spec. In those situations, an on-car brake lathe is ideal.
 
Last edited:
Messages
2,028
Location
WY
I've had rotor pulsation issues in the past on my wife's vehicles. She just doesn't understand the concept of downshifting coming down a steep long grade near our home. The OEM rotors are cheap to buy in my vehicles but I have bought aftermarket drilled/slotted/coated rotors and pricey carbon ceramic pads for her vehicles. No more issues and less wrenching time for me.
 
Messages
1,752
Location
Cincinnati, USA
Originally Posted by sdowney717
Originally Posted by Cujet
It's good to know that if a rotor warps when hot, it's going to warp when hot after it's been turned. One thought is that the recycled metals are distributed unevenly in the disk. Another is uneven cooling, the metals in one location were "tempered" by a red-hot stop, then keeping the pads clamped on that location while the rest of the rotor slowly cools. Regardless of why it happens, "IF" you experience heat related warping, replace the rotor.
https://www.onallcylinders.com/2017/05/19/6-biggest-brake-rotor-myths-debunked/ Rotors do not warp. I am a mechanic. It is a myth. I did turn one badly once and since it was not true it pulsated and had to get re-turned. https://www.brakeandfrontend.com/warped-rotors-myth/ https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3043065/1 https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3895543/all/Brakes_Rotors_DON'T_WARP__-__A
Brake pulsating is usually hard deposits on a rotor instead of warping, but they do in fact warp in a small % of cases. This is usually due to excessive lug nut torque and/or driving like a madman with hot brakes then going through a water puddle to rapidly contract them. In fact it is very easy to see on a lathe when it starts cutting into opposing sides instead of evenly, or just using a high precision flatedge against the surface. It is funny when an almost-myth is countered with another myth. Rotors do warp, but that's far less common. As far as turning rotors off vehicle, it had worked fine for me for many years, but then they started making rotors thinner so there is often too little material left to bother, which doesn't make on-vehicle any better, and access to lower prices online made it even less cost effective.
 
Top