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Discussion Starter · #1 ·
I was talking to one of my customers today. He's an old time Mopar man (4 mint RCs, 2 mint Rams, assorted Hemi powered 300s from the 50s, owns a repair shop). He advised me to mount my new rotors on the hubs then have the rotors cut while mounted on the hubs. He said it had to be done to keep the rotors from wobbling as I may not get the rotors on the hubs flat. Makes sense. Has anyone done this? I've never heard this mentioned in any of the threads or How-Tos. Thanks.
 

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Yes I have heard that many times before. It's old school stuff that works.  {yes} ;D
 

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a couple points to ponder.
not old school stuff.on car wheel balancing was old school.
on -vehicle rotor machining is the latest and greatest to get zero runout.very good on performance vehicles.all depends on the technician.its a pain to set up,most techs wont do it because its time consuming.in the 8 months i worked in the ford dealership i never saw the on-car rotor surfacer used once.i wanted to learn how to use it,nobody was willing to demonstrate it.they would sooner chuck it on the lathe and carry on.(lets dont and say we did)i specified exactly how i machined when i submitted my worksheet.i never had a request for on-car machining.i wanted to,mind you.....

hub surfacing discs are readily available ,its like a scotchbrite surface conditioner disc for the die grinder but has a hole in the centre to clear the wheel stud.once rust scale is removed,it should be very close to original.one for the 1/2" impact is also available.

all of this is irrelevant if wheels are installed incorrectly without the use of a torque wrench set to manufacturer specs.the discs can warp if torqued unevenly.

all calipers have built in compensators for minimal runout.the guide pins or slides.they will however not compensate for varying thickness.
usually thats where the most noticible brake pulse emits from.

when i was in parts i had one shop that would complain about brake pulse or pull from almost every new rotor.he refused to clean the rust inhibitor after mounting the discs.big no no.that oil or wax used to keep rotor from rusting will contaminate the new brake pads.causes undesireable brake performance.
 

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offroader_dodge said:
a couple points to ponder.
not old school stuff.on car wheel balancing was old school.
on -vehicle rotor machining is the latest and greatest to get zero runout.
The midas my wife used to work at has been doing this since the 90's at least that I know of. ;)
 

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Personally, I view doing it w/o regard as a wasted effort/money. I also view cutting new rotors w/o measuring them in the same light.

I've used both, the on car sucks from a user stand point. Then there is the fact it allows up to 4 thousandths head wobble according to the user manuals. The manual mentioned something about leaving the opposite wheel on while cutting. Absoltuely doesn't work right when you have wheel/tire combo that doesn't balance well, such as most 4x4s.

What would I do? Non directional swirl pad like off roader mentions plus measuring run out.

Then again, if you have a good flat rotor that has excess run out when mounted, you need to be repairing the bent/loose/damaged axle/hub parts, not offset cutting a rotor.

It was meant as a short cut for brake guys who didn't want to have to remove unit hubs, but ended up taking even more effort to setup and use.

Did I mention I hate using that crap? ;D
 

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Discussion Starter · #6 ·
Thanks for the replies! I'm hoping to finish this weekend.
 

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In my opinion, the best way to turn the old style rotors like on our trucks is on a lathe with the hub.  Properly mounted, they turn true and if the lathe has a nice surfacer, they are just like a factory rotor in my opinion and much better than the ones that turn them on the vehicle.  I have the best luck turning the rotors on a lathe with the rough cut at low speed, then finish up with a thin, high speed cut for a better finish, then I usually just used a typical sanding block with 120 grit sand paper to smooth them out a little while they are still turning on high speed.  So far I have not had any complaints from those customers that I turned their rotors like that and all of mine have broken in fine with no squeaks or pulsing.   It's very easy to screw up a rotor while turning it, but it's not that hard to get good results either.  Now the stupid little FWD rotors with the stamped steel hats and welded disc are another matter entirely.  It was a very good day when I could turn one of those without them howling and screwing up the cut.
 

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Elwenil said:
Now the stupid little FWD rotors with the stamped steel hats and welded disc are another matter entirely. It was a very good day when I could turn one of those without them howling and screwing up the cut.
You turn them? ??? I thought they were throw away rotors............. {yes}
 

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Well if I had my way we wouldn't have turned them but the home office in Staunton had other ideas, lol.  If there was a spec available and the rotor had enough thickness to turn, we were supposed to turn them.  Generally we told the customer that they had a 20% chance of coming out ok if we turned them.  They would vibrate bad because you could only put the skinny little weight band on them and it didn't do squat.  Some of them ended up with nice swirled gouges and you could actually watch the rotor flex as it vibrated.  Other times they turned ok, but I always warned the customer about how they turned.  Naturally a few commented that we were just trying to sell him new ones rather than the $7 per rotor charge to turn them so I would occasionally have to let the customer watch me attempt to turn them which was always fun.  I think a lot of it had to do with the fact that people frequently overheat their brakes around here in the mountains and the heat cycling tempers the thin rotors and makes them hard to cut, but that's just a theory of mine.
 

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then there are those that don't realize you can drive if you foot is not on the brake!
 

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The last couple of cars I have had that had rotors turned, didn't last.  The fronts on my marquis were warped again after a week of driving, and I am told I drive like a grandma. :-X
 

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If you torque the lugs as per the service manual, you'll easily get 100k+ miles out of them.  On my mother in-laws car (which she bought new off the lot), I didn't have to put new rotors on until the last brake change at about 150 or 160k miles.  The wife took her car to the tire shop to get a flat tire fixed and rotate them when I was out of town.  They never torqued the lugs when they installed the tires.  Now, I've got to turn the rotors and the drums because of pulsing brake peddle.
 

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Dodge 85 RC said:
The last couple of cars I have had that had rotors turned, didn't last. The fronts on my marquis were warped again after a week of driving, and I am told I drive like a grandma. :-X
Grandmas ride brakes. I notice some cheaper autozone rotors are made physically thinner. Not outside dimensions, but more air gap in the vane area. Same with some of the rotor hats.

Elwenils experiences sound about right. The on car produces a rougher finish. Then again, with any used rotor on any type of lathe, you can have "hard spots" that will not machine out. The tool bit will actually jump over those spots. The rotors are junk at that point.

From my understanding, once the rotor gets so hot, the crystalline structure changes and hot spots combine with brake pad material to form a hardened or heat treated area.
 

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i tried to machine a set of ford rear rotors,didnt matter what speed,what cutting rate how much i cut the bloody thing howled.it made such a mess,i had to use a grinder (toolpost) to make it useable until a new one could be brought in after the weekend.i told the boss it wouldnt work.why doesent anybody listen  ???
when it came to those stamped/thin junk rotors i stood my ground,i NEVER cut them,period.
fire me if you want,or do it yourself.....
rotors that repeatedly warp most always have another issue like bad rear brakes or a sticking caliper
or the famous metal bracket on the hose that rusts and crimps the hose shut.
 

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Discussion Starter · #15 ·
Thanks again to everyone who replied. I am using new rotors. They look pretty beefy so I'm hoping with new pads, bearings, tierods and shocks plus proper torque specs everything will be good. Now to get the axles out.......
 

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Stepside Billy said:
Thanks again to everyone who replied. I am using new rotors. They look pretty beefy so I'm hoping with new pads, bearings, tierods and shocks plus proper torque specs everything will be good. Now to get the axles out.......
Hook up your favorite dial indicator and you will know for sure.
 

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I just had to change rear roters on my 06 1500 quad cab...  Had them fixed under waranty but you know how dealers are... I picked up a set at Advanced auto for $70 each... They work great so fat.... Only had 20xxx miles on truck when the rear originals warped..
 

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RCC official Stir stick said:
I just had to change rear roters on my 06 1500 quad cab... Had them fixed under waranty but you know how dealers are... I picked up a set at Advanced auto for $70 each... They work great so fat.... Only had 20xxx miles on truck when the rear originals warped..
Make a mental note of the pad types you have used. It's usually not the rotor's fault for warping...the combo of braking style, vehicle weight, and pad type usually cause the overheating damage. :)
 

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Discussion Starter · #19 ·
s ǝoɾ said:
Hook up your favorite dial indicator and you will know for sure.
That's probably my best bet!!!
 
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