I've read in several places that the major cause of warped rotors is improperly torqued wheel lug nuts. They should all be torqued in the range of 72 to 87 ft-lbs (80lbs isjust right).

When you take your car in to get a new set of treads, make sure that they hand-torque each lug nut. The vast majority of tire dealers don't bother to do that.

 

Thanks. Can we get out of 1998'?

 

Sure. That will be my next mod.

 

Yeah that's true. My friend had the rotors warp on his Impala a few years ago because NTB over-torqued them.

 

Well then - excuse me for being the dumb one, but can somebody please explain to me the mechanism involved by which a rotor is going to experience this warping effect?

To me it looks like you have a flat flanged hub about 15mm thick that the rotor runs against - rotor itself maybe another 10mm? - and the wheel rim bolting to the hub and rotor adding yet another 10-20mm - so now how much pressure (Ito hundreds of tons per square inch) is needed to cause liquefication of any/all and in particular the rotor material alone?

My logic would dictate that the typical Magnesium/aluminum compounds of the typical Maxima rims will undergo liquefication a lot earlier than either the rotor or the hub steel components and will deform a lot earlier ............. no?

My guess is you gonna have a deformed rim and broken wheel studs long before you are able to use the pressure of 5 over-torqued studs of 12mm to deform the rotor material ..........................

30+ years buggering around with cars/bikes/4X4s and have never seen/experienced the rotor deformation myself and don't know anybody that has either - so help me out here........................

 

I've seen it documented in many places that it can happen. Here's just one example from Yahoo:

"What causes a rotor to warp? Overtorquing or unevenly torquing the lug nuts with an impact wrench is a common cause. For this reason, most experts recommend using a torque wrench to tighten lug nuts when changing a wheel. There are also special torque-limiting extension sockets called "Torque Sticks" that can be safely used with an impact wrench to accurately tighten lug nuts. But a plain impact wrench should never be used for the final tightening of the lug nuts because most provide no control whatsoever over the amount of torque applied to the nuts."

As far as the how, I would think that overtorquing or unevenly torquing would interfere with the ability of the rotor metal to expand and contract due to heat.

 

I can see that uneven torquing can interfere with the expansion characteristics of the disks when the vehicle/brakes are seriously abused and the rotors are expected to operated at hugely elevated temps, but once again I can see the actual rim deforming a lot earlier also under those conditions, and by doing so actually nullifying the supposed over-torquing influence on the rotor

 

This is the part where I start grabbing at a straw or two. Okay, looking at the issue from the perspective you pointed out, the temperature of the wheel would have to get pretty close to the temperature of the rotors. Correct? I'm no expert on metallurgy but don't the wheel, studs, and rotors conduct heat at different rates? Also, the wheels get better airflow than the rotors do so that would keep them cool. So, between these two things, wouldn't that greatly reduce the chances of the wheels deforming first?

 

The actual wheels do indeed have better cooling, and there is no doubt the different materials conduct heat at different rates.

I am also no metallurgical boffin, but simply thinking about the relative hardness and malleability of the materials involved, I have a "feeling" that the rims will deform and negate (to a very large extent if not completely) the "over-pressurization" or "excess stress" placed on the studs caused by overtightening the nuts way earlier than the onset of rotor distortion.

I would have to say based on personal experience, that the practice of cleaning, with a jet of cold water, a vehicle that has been driven for distance with hot wheels, will more likely cause local rotor distortion (? - surface hardening?) due to local and non-uniform/extremely fast cooling.

I just have a gut feeling that overtightening alone is not the cause of distortion, and that there will usually be another undisclosed little saga that surrounds the discovery of "warped disks"

Cheers for an intelligent chinwag and sharing of ideas.

 

Hey, I always love a good clean discussion. I guess the final answer will require some research.

 

The answer lies at the heart of the most basic of questions:

Why bother with torquing nuts at all?

I should have clarified my post by saying that uneven torquing will warp rotors, but overtorquing can have the same effect.

Here's why:

It has to do with maintaining the uniformity of the bolt threads. The threads of a bolt are its weakest -- and thinnest -- points. Take a micrometer and measure the edges of your wheel stud (bolt) and compare that to the thickness (diameter) of the bolt itself. The threads, and not the body of the bolt do all the work.

Ask yourself, "How much pressure would it take to distort them?

The answer is, "a fraction of the pressure that would be needed to bend the bolt itself."

As your tires are spinning at highway speeds, a temendous amount of centrifugal force is exerted on them. The force literally tries to rip the wheels off the rotors. Overtorquing causes the threads to distort (bend outwards) inside the lug nut, and inside the hole in the wheel. As a result, stresses are shifted to the outer diameter of the rotor instead of being concentrated. and equally distributed, at the center.

Now, the real demon is unequal torquing.

 

Man - there are so many wrong assumptions in that post of yours its just not funny - so at the risk of starting a flame war:First thing - the bolt's threads have no contact with the rotors - the locking splines and underside of the flat head sections of the bolts are all that is in contact with the rotors - the uniformity of the threads can therefore have no direct effect on the rotors.The thread part of the stud material is attached to the center core material of the stud, and for the threaded part of the material to be able to do anything useful, the load is transfered internally to the core of the bolt too because the threads are physically part of the bolt - as long as you do not over-tighten the nut to the point where the threads undergo irreversible distortion by exceeding axial sheer strewth of the material (starting to strip it) a good part of the axial load on the stud is actually carried by the center core of the stud material. Quite irrelevant IMO. There is simply no danger of ever "bending" a stud (as long as the wheel is securely attached to the hub by all the nuts being present and tight) because there is wheel locating shoulders machined into the axle hub to carry the radial loads on the hub transfered from the wheels movement and the weight of the car - IE - its the purpose of the wheel studs to keep the center of the wheel located on that load carrying shoulder of the hub.Absolutely correct - except that the wheels rotational centrifugal force has squat of an influence on either the rotor or the axle as long as the wheel is balanced!. The centrifugal forces caused by rotation tests only - and only - the material strengths of the wheel's material - thats all. See previous point - if the wheel is balanced, there is absolutely NO force transfered to the rotors because of the wheel spinning - at whatever speed you care you mention.Read my fist post in this thread, and then with the comments I made in this particular post it should be obvious that you are either ill-informed or uninformed as to the structure and workings of a wheel hub/rotor/wheel assembly.

Its as simple as this : ANY torque you apply to the nut gets transformed into a axial load on the stud because of the characteristics of the threads - the axial load on the stud excerts a force in such a way that it tends to clamp the axle flange, the rotor and the wheel together. As long as you torque the nuts to a point where the wheel is always kept on the load carrying shoulder of the hub, there is no "load" transfered to the outer edges of the router .......................

 

In your 30+ years of "Buggering around," you must have picked up a lot of knowledge. Too bad that how to be humble and not condescending was not one of them.

Rather than pick apart my post, paragraph by paragraph, to show how much smarter you are than I, you could have simply posted your own take on the subject without any disparaging references to mine. I may have sounded authoritative, but I was citing my opinions -- which I am sure you are doing also, and not quoting chapter and verse from Nissan TSB manuals.

There is one, self-proclaimed expert" named Caroll Smith who claims that rotors do NOT warp for ANY reason, but there are thousands of others (6,550 hits on Google) who say otherwise...that overtorquing warps rotors:

A small sampling:


From Canadiandriver.com, January 200:

Incorrect tightening of the wheel nuts also can warp a rotor. When installing a wheel, snug up the wheel nuts and then tighten them in two stages using an alternating criss-cross pattern. Using a torque wrench is critical on modern vehicles. Some shops tighten wheel nuts with air impacts. Others use "torque sticks" designed to limit the torque on the nuts. Neither is accurate enough for today's cars. Make sure they use a torque wrench. If you experience brake pulsations after changing a wheel, loosen the wheel nuts and retorque them. If this is done as soon as possible, the rotor will usually correct itself. Leave it too long (more than 1000 km) and it remains warped.

From Advance Autoparts website (http://www.advanceautoparts.com),

Another cause of warped rotors is improper wheel nut torque. Over-tightening of wheel nuts can cause undue stress and warping of brake rotors. The best solution is to use a torque wrench. This is an especially important consideration with aluminum or performance alloy wheels. Proper torque values are also crucial when refastening slider pins, caliper mounts and associated brake hardware. A service manual is the best place to find the correct information on brake and rotor replacement procedures. When working on your brakes remember that "good enough" simply isn't. Taking the time to do it right is the best and safest route to take.

From Ponytales.com:

Although some shops adhere to manufacturer's lug nut torque settings when they install wheels on your car, lug nut tightening is still relatively haphazard. It shouldn't be because safety and part's longevity can be adversely affected when lug nuts are tightened incorrectly. The "why" can best be explained by realizing that lug nuts need to be tightened evenly so the stress they impart to wheels, hubs and, brake drums or brake rotors is evenly distributed. When stress isn't evenly distributed. wheels can bend or break, brake rotors or brake drums can warp, and wheels can fit unevenly on the hubs.

From Raceshopper.com:

Over-torquing lug nuts is one of the most common causes of warped rotors!

Here are some more links...

If the lug nuts are not tightened evenly the rotor can warp and you are back to square one. http://www.autoeducation.com/autoshop101/brakes.htm

When installing the rotors, use a torque wrench to OE specifications. Do not use an impact wrench. Excessive or uneven torque will warp the rotor. If one lug nut or wheel stud is 20% tighter than another, you can have a run out on the rotor greater than 0.005, which translates to a “warped rotor.” http://www.brakewarehouse.com/brkewrhsefaqs.htm#topmyth

10 lbs of differential can distort a rotor 0.0001"-0.0002"
http://www.thedieselstop.com/archive...o=&fpart=1.htm

Warpage may be caused by several factors; over tightening the lug nuts. http://www.braketru.com/brakenotes.html

ONE THING IS CLEAR: OVERTORQUING OR UNEVEN TORQUING CAN CAUSE TOROS TO WARP.

However, "Why" that happens seems to be a mystery.

After searchng through 90 pages of Google links, I failed to find a single one that provided a true, scientific explanation of why rotors can warp from overtorquing or uneven torguing.

I gave it my best shot, and considering that I am as far from being a phyisicist as you are from being a humanitarian, at least I contributed something resembling an explanation, versus your contribution which added squat to our understanding of the reasons why rotors warp:

 

The following link my give you some ideas on the so called rotor "warpage" and runout problems and other brake stuff. This is not only a Nissan issue. [URL=hostingprod.com/@aa1car.com/library/procut02.htm] The Nissan repair procedure for pulsing/vibration etc. during braking is covered in TB NTB00-033a.

 

A few years ago I posted a question asking do you guys actually think mechanics are breaking out torque wrenches to tighten bolts, studs, nuts, etc. In the real world the answer is no. Most mechanics do not use torque wrenches. It doesn't matter if it's a mechanic at PepBoys or at a dealer, torque wrenches are not being used as much as you think, if at all.

I've worked in the industry, and unless I'm rebuilding the internal components of a engine I've always used my air tools to tighten all my bolts. If not my air tools then my hand tools, but hardly ever did I use a torque wrench.

Have I ever had a job come back due to a loose or over torque fastner, no.
In the flat rate industry you don't get paid for "come backs" due to your fault.

Can I say for sure all the fastners I've tighten with my air tools or hand tools have always been to spec, no.
It comes down to knowing your tools, the size of the fastner your tightening and the material that's being tighten down (aluminum, iron, plastic, steel, etc)

When I post this question a few years back I challenge all those who don't believe to go to a auto shop that you trust 110%, observe that mechanic(s) for one hour and see how many times he uses a torque wrench when he tightens anything.

My $0.02

 

This article supports the overtorquing/uneven torquing causes of rotor problems. Some quotes from the article:

 

I guess overtorquing could do this. But I bet you would have to REALLY go overboard and or REALLY be inconsistent on the lugs. Basicly be a moron.

 

Sigh ........... as I said - at the risk of starting a flame war.........

 

i have been told by many mechanics that when remounting a tire to put all your weight (i.e. step on top of it and bounce a little) on the lug wrench. Is that too much? should I be hand tightening?

 

WTF? Depends on how heavy you are and how long the wrench is. Even a 160lb person can get well over 150ftlbs torque on lug.

 

If you look at the BACKSIDE of the mounting flange of a wheel you will find that it is not completely flat, but scalloped (steel wheels), or is spotfaced or has cast steps (alloy wheels) at least at each lug nut location. This is a design safety feature so that when the lug nut is TORQUED it creates a "springback" effect to help prevent the nut from backing off. In other words at each lug nut there is effectively a honkin' big spring washer. This is really designed for the people who couldn't torque 4 or 5 lug nuts equally without a torque wrench to save their own life (and not have a lug nut backoff). The auto manufacturers don't like it when wheels come off their cars. The problem is that because of the gap/space created on the backside of the wheel to allow for this feature, that if you really overtorque/unevenly torque these lug nuts you can distort (pull in) the hub flange and rotor flange to the point of causing the brake pad contact surface of the rotor to distort beyond lateral runout limits causing uneven wear (thickness and flatness) and the usual pulsing effect. Also the engineers get their knickers in a knot when there are parts in a "stack" like we have with the wheel, rotor and hub where there is unequal "clamp up" loads applied to the stack by incorrect torqueing procedures. Incorrect or lack of clamp up (bolt up) can cause relative motion of the parts in the stack causing wear (fretting) and subsequent loosening and failure. There is a lot of high priced help in the industry dealing with this and OTHER brake issues that we see on our cars so I urge everyone to read the info at the URL address that I listed in my reply above.

 

Gee...that is sort of like saying, "Don't take this personally, but I think you are a *******."