Brake Rotor Machining

The factory manual for my 2000 Concorde LXi states: "...the rotor should be resurfaced using a hub-mounted on-car brake lathe..." This implies that the
dealership rather than the owner is going to do this job... or do brake shops and service stations usually have this machine now? Apparently it's not recommended that the discs be turned on a bench. What can happen that could go so wrong if the machining were done to spec?
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If the rotor is not grooved and is not warped and it still exceeding the maximum thickness, then change the pads and leave it be. If it is damaged, throw it out and buy a new one.
Ted
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This brings up another point where experience would come in hand; the condition of the rotor. The manual says "If the rotor surface is deeply scored or warped..." ... but I don't know what to make of what I observed. I found the rear rotor smooth when I ran my fingernail across the surface (but I didn't repeat that anywhere else on the rotor. That leaves a lot of surface unexplored.) The front rotor proved different, however. I didn't find a "deeply scored" surface but I did find what seemed to be a few hair line beads around mid way into the surface that could be sensed by my fingernail. These weren't groves. They felt like very small bands raised ever so slightly higher than the main surface. The brakes don't squeak but I do feel a slight pulse at the very end of a brake session when the car is braked from high speed. At lower speed when I feather the brake to stop easily, I get nothing. I've been told by one mechanic that "if it pulses at all, the rotor is warped. Replace it." I've since found that man's credibility at stake; he also told me his shop doesn't use the hub-mounted on-car brake lathe because "it costs too much in time and labor to hook all that up."
Q1) Any comments about the pulsations? Q2) When I do this job next week, maybe I can take the rotors in question to my Chrysler dealer and let them look at them. Would they be able to tell? I trust the guy I deal with... for the most part. :-)

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John Gregory wrote:

The more I mess with brakes, the more I'm convinced that what we call warped rotors often is not that at all. It's a knee-jerk response any time we get vibrating brakes. One possibility is inconsistent pad filming (that can change with hot brake application) - could explain what you're seeing. I've just about concluded that pads can be as or more important than rotors in preventing vibration (the filming thing).
Not to sound like a commercial, but I had problems on my last set with Akebono ceramics. I can't prove it, but I think the pads were filming horribly. When I got new rotors, I changed the pads to Performance Friction's Z-Rated™ pads at the strong insistence of the rotor manufacturer (their engineer said that they have had a lot of rotors returned due to vibration problems only to find that certain ceramics were filming them and causing the problem). Anyway - My '99 Concorde brakes have been razor smooth for the longest period of time since I've had the car since making that change.
Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')
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John Gregory wrote:

I asked a lot of service garages the question of on-hub vs on-bench turning of brake rotors. The consensus is that if the rotors are not integral with hubs (ie if they just slide off the lug bolts) then they are taken off and turned on a bench.
Apparently some european rotors can't be taken off and are then turned on wheel-mounted lathe (which is more expensive).
I think that wheel-mounted lathes are not exactly rare.
What is happening is that (as I found) Chrysler wants to sell you on a more expensive proceedure rather than the $10 or $20 per rotor to have them turned on a bench.
They would rather have you buy new rotors, but if you're insistent they will turn them, but in your case they're rather use the most expensive method.
I brought my rotors to (oh I forget where) and had them bench-turned last fall for my '2000 300M. I had quite a lot of pedal pulsing and steering-wheel-shimmy that completely disappeared after turning the front rotors. I'm positive that the rotors weren't warped - but that the pulsing and shimmy were caused by surface pitting.
Dealerships use rotors are a scam, and many people have been "trained" by the dealers to thow the rotors out and buy new instead of turning them. I think surface pitting is probably the cause of most rotor problems these days (cars are lighter then they used to be and hence warping is more rare, and warping caused by over-tightening the lug nuts is an urban legend these days).
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same price for either here $130(wich is high IMO)

We have and use one.

At our price purchasing new rotors is sometimes cheaper.

I have not been "trained"in this manner. rotors have to be measured here and the measurements written on the R.O.and initialed by the shop foreman.
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the dealer i work at sold the on the car lathe it was a waste of money if i find any rust pitting on a rotor it replaced with new, like cancer you can't stop rust and it only gets larger and it is a issue not to over torq. the wheel lugs because the hub metal is thinner these days
MoPar Man wrote:

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tim bur wrote:

I think you meant "said" when you wrote "sold" (above).
It may be a waste of money (or, it _is_ a waste of money), but is it necessary for removable rotors, is it faster, or is it a "premium" service option designed to make the customer throw in the towel and say yes to new rotors?

Do you ask the customer first? Do you tell them that turning the rotors will probably get rid of the pitting? Or is it easier for you to not get your hands dirty and pull a new set from the parts dept. and let the customer pay $350 for the whole job instead of $40 to turn the rotors?

Rust will start on the new ones the minute you get the job done and you take the customer's car to the wash bay to give the car a wash before you hand the keys over.
Turning the old rotors will get rid of practically all the pits and give you a surface equivalent to new rotors.

You'll break an alloy wheel (or strip a lug) before you apply enough torque to distort a hub. You will not distort 2 inches of solid steel by over-tightening a lug nut.
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I think he said he sold it because it was a waste of money. And I have to disagree about not being able to warp rotors by mis-torquing a wheel. It is a VERY common problem on some makes and models - wheel lugs SHOULD be accurately torqued, not just slammed on with the impact cranked right up.
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It is faster and easier to mount the hub mounted barake lathe then to take off the rotors bring to the bench mount them, then take off and re-mount on the car. Just bolt the hub mounted lathe and it is done in less time.
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hiya,
Just replace the rotors instead. Here in Blighty, getting the rotors turned costs about £10 and new ones are about £20-£30, (pt cruiser, ford granada and the jag) factor in the added downtime, needing another car or a friend to take the things to an engineering shop and then fetch them back again and the new ones can work out cheaper. A problem I've had with vented discs before is that the cooling vanes down the centre of the rotors can crack and cause different expansion rates along the disc, which will run true when tested cold but then warp when hot, and cracks are regarded as 'a bad thing' Also, when trying to stop nearly two tons of car from three figure speeds, I want the things to work, more metal = more cooling = less fade
m
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On Sat, 18 Jun 2005 19:20:07 +0200 (CEST), Nomen Nescio

Thats fine if you don't have salt. Road salt gets into the system and screws everything up. As for pad material, softer is NOT ALWAYS better. Carbon Metallic pads are hard. So are ceramics, and when salt is an issue they stand up better than any soft organic - and I mean the rotors last longer.
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My experience with rotors (especially on the '96 T&C) is that they seem to warp when new. That's not always true, as the set on the car right now have been OK. Once they warp and I get them turned, they don't seem to warp again.
I don't have a good explanation for this. It's almost luck of the draw. I have always used a torque wrench, criss cross pattern, tightened in steps, etc. When all is said and done, this seems to have no effect whatsoever on if they will warp or not (at least on the Chrysler).
So I agree with the poster who poo-pooed the holy ritual of carefully torquing the lugs. All it seems to do is make you feel righteous.
Ken

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My '97 has always had warped rotors. I finally bought a dial indicator and base & did some further investigation. I always thought both sides were toast. It turns out in this case only one side was out- and this particular (new) $50 rotor was not warped but was out thickness wise. I bought two new rotors, one was a Raybestos PG+ (same as the shot one) and the other was a Chinese made off brand for $17. I put the cheapy on as a guinea pig - its been doing fine for over 5k miles now. I kept the PG+ as a spare along with the NEW PG+ with the thickness prob. Before uncovering the thickness issue, I also used a 3M Roloc on a die grinder to get rid of the oxidation on the alloy rim to rotor mating surfaces.
I've owned a plenty of cars,trucks and vans with disc brakes - this is the only one so far that has such delicate, sensitive brakes requiring calibrated tourque wrenches and apparently on the vehicle turning equipment. Drum brake wise, my '69 dart is another matter ;-)
Bottom line : Get a dial indicator + base & diagnose what is really going on. This really sheds a bight light on the issue. (Harbor Freight has a magnetic base & arm on sale for around $8 - they also have cheapy dial indicators)
Mark

have
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Mark wrote:

Excellent point, Mark.
If more people aware of using dial indicators to actually measure runout on a brake rotor, there wouldn't be such a vacuum of knowledge on the various forums as to actual root cause of brake vibration (i.e., to rule in or out rotor warping) on specific platforms. I was aware of using them, and in fact have borrowed them over the years from my employer at the time, just never in later years (for my LH car). The other problem is that people are not into putting the effort into the attention to detail and time it takes to make the runout measurement - even if they were in everybody's DIY garage.
I would love to take my previous pair of front rotors and have them thoroughly analyzed to determine if: (1) One or both are or are not warped, (2) One or both have thickness variation, (3) And/or there was a non-uniform filming issue with the particular pads as I suspect.
Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')
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