Brake shake with freshly machined rotors?

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| | | > Where does the warpage come from? You're sandwiching steel between steel. | > There is nothing to give or bend. | | They can both bend.
| When you tighten a lugnut to 100 ftlbs, it can apply thousands of PSI | to the rotor/hub, more if using an impact wrench. | Steel, cast iron etc all bend easily under such forces. | HTH | Ben
The torque applied to the lug nuts does not have to bend /warp the rotor. All it has to do is apply uneven pressure to the rotor. After that heat will finish the job much the same as heating a metal plate or rod while applying pressure to it. With the materials they are using today it doesn't take a bunch of panic stops to do it. Heavy traffic, coupled with the driver riding the brakes could well cause the problem.
My Safari started showing signs of warpage after the first aftermarkrt brake job. I think I will buy all new OEM parts and do the job myself. New rotors, drums, pads and shoes.
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In order for that tho happen the rotor has to shift it's position. Between two flat pieces of steel?

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If anything the weakest part is the stud. it would stretch.
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My theory:
You are sandwiching aluminum between steel. My guess is that the hub flange gets warped when the studs or threaded holes are pulled with excessive force into the fairly soft aluminum. The aluminum between the holes does no bend and thus the flange, and rotor warps slightly.
Steel rims are not susceptible to this as it is much softer between the holes.
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What do you mean by aluminum between steel? Likewise "the aluminum between the holes..."

... and by the statement above?
Sorry - but I'm just not following what you're trying to say.
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The studs/hub flange/rotor is steel. On that you put an (soft) aluminum rim, which often has a solid flange, and you clamp that with steel nuts/bolts.
I think an analogy is if you put a flat sponge on a table and a flat piece of (printer) paper on top of that. Now spread your fingers and push them down against the paper. Watch what happens to the paper as you increase the force. The rim is made of soft material like the sponge.
If the clamping force against the rim had been even, instead of concentrated around the bolt, this would not be a problem. The flanges would not deform.
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Got it - sorry for being slow. If the difference in torque was very dramatic from one stud to another, or more so, if one stud was dramatically tighter than all of the rest, then I could see a problem. Not so much with the more minor differences being spoken of here. Plus - you don't have a sponge, as in your analogy. You have a steel rotor. Mounted to that is an alloy wheel. Both have more rigidity than your analogy. Reasonably tightened lug nuts aren't going to present the same kind of pressure that your analogy suggest, against a very flexible material.
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news:aab2d$4a435d5e$452897e0 >Reasonably

Right, keyword is "reasonably". I have seen them go from just over finger tight to extremely tight.
I wont argue the issue, but will continue to do what I do, as I believe it is better to be overly nit-picky than rambunctious with wrench. I have seen it repeated many times, and that is good enough for me.
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wrote:

But the aluminum rim is on the outside. The rotor is between.
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labatyd wrote:

of fasteners, along with the thermocycling (especially extreme changes like water puddle quenching or pad bake at the end of a really long stop and mashing the pedal down for a long time, which causes localized hot spots and pad material transfer). The three things you can control as a driver are 1) driving through less puddle with smoking hot brakes 2) not holding the pedal down hard after a long hot stop - creep a few inches a couple times and lightly hold the brake pedal instead 3) torque your own wheels to spec. The only thing a tech can do for your car is #3.
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I do believe you could also perform #4 on a horse.
I've found that if an automotive engine is missing, it's usually due to an ignition problem, such as old plug wires or a weak coil. Conversely, if a horse is missing the trouble is often in the fuel system. Try administering additional oats, perhaps augmented by a few carrots and sugar cubes.
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wrote in message

Here's my problem with that... it seems to be very anecdotal. I have seen the same kind of problems on properly torqued wheels. My experience with tire shops is very different from yours, though I do not question yours. Mine is that they all use torque wrenches these days, and it has been years since I saw a tech hammer a lug nut on with an impact.
My experiences are that rotors can be of low quality today - especially the budget rotors, and it does not take any amount of heat to warp them. Torqued lug nuts or not, they warp. I've also convinced myself that the cheap pads add to heat in the rotor and that ceramics do a much better job of dissipating that heat, thus reducing warping. I've used both semi-metallic and ceramics on the same model of rotor, and found a distinct difference between rotor anomalies with ceramics.
Contrary to that, I have also gone the route of meticulously torquing lugs, to find no notable difference between torqued lug nuts and those that weren't torqued.
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wrote in message

Rotors WERE beefier a few years ago, no doubt. I agree my observations are anecdotal, but they have added up to some pretty firm evidence (not proof, but evidence).
One of the Dodge van I personally experienced, a national tire chain installed new tires for me and in about a month the judder was there. Nothing before that. DT had used the torque stix.
I pulled the rotors, had them machined true, and reinstalled them along with new pads. Ran for two years that way with no problem whatsoever. Then back to the same tire chain and -guess what - within a few weeks the pulsation and judder was back. (Cause and effect thinking starts here.)
After than, I adopted the torque wrench only policy and have had no more problems.
I live in a small town. In a larger town, people have seen a torque wrench. Here, they dont have them at all in the tire shops, etc. And the warpage goes on. We had another car, a Buick, that suffered the same problems after new tires were mounted, whereas it had none before....it is was NOT a tire problem.
I have a long list of them. For me, it doesnt take but a few seconds longer to torque the studs, star pattern.
Anyone who wants to ram them on with an impact wrench, go ahead. (I have an impact wrench and use it for some front end work but not for tires. I am not that lazy.) I am convinced it is not to my best interest.
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news:abc03$4a3f7939$452897e0

Oh one more thing, in all the cases I have noted, the judder does not occur immediately. It starts days to weeks after the action (new tires, pad replacement, rotation) which I believe initiates it. This, in my mind, supports warpage with heating of the rotor.
If you read the Babcox reports, they mention the problems of hub runout and thickness variation. If that were the cause in these cases, one would notice the shudder immediately. Thickness variation may be corrected by machining the disc, but hub runout wont be - unless the rotors are machined on the car.
And further they mention the possibility of shimming the rotor/hub, or even indexing the rotor with respect to the hub irregularity, to minimize this problem.
It is an interesting subject and, again, you can do what you want (but not on my cars ;>)
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wrote in message

I agree with this observation. I have concluded it to be related to semi-metalic pads, as I don't see that now that I've switched everything over to ceramics. I've also upgraded rotors that I use, but even with the upgraded rotors, I found the problem could occur (only not as regularly) with semi-metalics.
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wrote:

There could be hard spots on the rotors. And perhaps while it was sitting the area where the calipers were that did not rust is now either harder or softer then the rest of it from that, although I would not give that high odds. I had a impala back in the 70's that did what you were describing and they only fix that worked was new rotors.
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wrote:

Just a suggestion: when you take a car in for warranty work, never ever tell them 'how' to fix it. When you suggest a repair technique, that is what the do, nothing else, because that is what you asked for. Instead, give them the symptoms, make sure they can duplicate these symptions and say: "Fix it, warranty". Heck, even if it is not warranty, don't suggest how to repair a fault! People make this mistake over and over--the shop must do what you suggest even if they know it won't fix the problem, and they cannot fix anything else because you asked for a specific action to be performed.

Never assume. Let the shop/mechanic find teh problem.

Well, first, a warranty repair should be done ASAP after the flaw is noticed. Don't wait for other problems to appear. Second, don't assume what is causing a problem. Now the dealer can say the did what you asked, and will be reluctant to do more.
Possibly bad rotors, as you suspect. They could easily be warped, or have excessive runout. Can't say until diagnostics are performed.
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And when you do tell them you want something, ALWALYS get a price. I learned that the hard way....I asked them to replace the brake retainers figuring they couldn't be more then a couple bucks each. When I got the bill I was about to call for the manager to figure out why it was $70 higher then I expected till I saw what they price was for the brake retainers......
When you suggest a repair technique,

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Not true at all. They are not obligated to fix as you suggest, and generally don't.

Bull. Many of us know exactly the path of troubleshooting, and the more likely problems. Knowledge is worth acting on.

Bull again. The dealer will and is, obligated to take your input into consideration, but to also apply their training and skills.

Agreed. And man, oh man, am I glad for that. I was beginning to feel like I was doing nothing but disagree with you.
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On Sat, 20 Jun 2009 22:10:55 -0400, "Mike Marlow"

Not sure where you are, but consumer protection laws in most states govern this, and when a customer asks for a specific fix or action, they are required to do it. I've never seen a shop that would do something else, they risk the customer's rath and a complaint to the state if they do so.
That would be something like going into a bakery and asking for a loaf of white bread, being given a loaf of whole wheat (because it is healther) and that substitution being OK.

Clearly the OP didn't, or he would not have specified a repair that was ineffective and probably unnecessary. I saw no indications of technical skill, no indications of any diagnostic process other than 'assume', 'assumed' and probably a bit of guess and by gosh.

Again, no, this is not the way things happen. At least in most states. You ask for something specific, that is *exactly* what they must do, or do nothing unless you say so. So often it is inpossible to determine whether the customer's request is reasonable or going to resolve any problem, so the shop will do what the customer requests--provide that loaf of white bread.

Oh, hell, you can disagree. I'm respected in my field, and know what I'm saying (and when someone comes to me and asks for a specific repair or process, I make it a point to impress on the customer that I cannot ensure that the repair will do anything other than cost him/her money.
The OP would have been much better off just taking it in and saying: "Here is what happens, please fix it", instead of suggesting repair methodologies.
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