Can a brake rotor warp because of overtightening? 2

[frankiee]

Can a brake rotor warp because of overtightening a road wheel. My guess is - no

 

[patprimmer]

I don't see how, unless the hub also warps, and even then it's doubtful.

Rotors vibrate from uneven wear due to uneven cooling when stopped with very hot brakes. The area between the pads cools off a lot slower.

Regards

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[ivymike]

I'm not sure exactly what you're saying about the wear, Pat. Are you talking about a bit of extra wear in the last few instants before the wheel stops?

It seems to be a fairly commonly held belief amongst car techs that overtightened lugnuts can result in rotor runout - examples can be found at valvoline's car maintenance site, this carquest tech bulletin

http://www.carquest.com/techbulletins/brakes/1999/CQB9921.pdf#search='cause of warped brake rotor'

http://www.indiacar.com/index2.asp?pagename=http://www.indiacar.com/techqa/3.htm

It's not clear whether what is being measured (runout) is a result of warpage or uneven wear. It seems as though either one might cause "pulsating" brakes.

 

[GregLocock]

/if/ overtightening one or more nuts means that the rotor is installed with runout, then it could cause a wear problem, which might be perceived as warping.

I think that's a big if, and easily checked by anyone with a dial gauge and a bit of nous.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

I think, from casual observation only, that if you drive hard down a mountain, then stop with the brakes very hot, the rotors are heat treated differently on the area under the pad vs the rest of the rotor. This might effect the hardness on that area only, resulting in uneven wear that eventually leads to uneven thickness that leads to uneven brakeing and pedal pulsation.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ivymike]

... but what difference does it make what the rotor thickness is in the non-contact regions?

 

[EHudson]

The '96 Ford T-Bird manual at hand states: "Caution: Failure to tighten lug nuts (1012) in a star pattern may result in high rotor runout, which will speed up the development of brake roughness, shudder and vibration."

Having had a lot of problems with warped rotors on this car, the components were carefully examined. The only thing that stood out was the very large chamfer on the inside of the lug nut holes in the rotor. The chamfers appeared to reduce the material thickness around the hole substantially.

The chamfers are an aid to installation over the studs but appear so large that high nut torque may cause local dishing of the area around the hole due to a large area of unsupported metal around the hole. I can think of no other reason why the wheel nut torque would cause significant distortion in the rotor.

 

[swall]

Was the '96 the MN-12 platform? Having worked for the brake system supplier for the T-Bird MN-12, I recall this this vehicle had brake feel issues due to rotor run out and other things.No clear root cause was found.

 

[Greenlight]

I worked for a Japanese auto maker and we studied "Brake Jutter" (pulsing pedal when stopping) in some detail.

We measured rotor runout on 400 cars with the rotor on the bench, with the rotors in subassembly, and with the rotors mounted on the completed vehicle using the on-line automated wheel torqueing equipment. These rotors were "special" hand picked rotors with less than 8 microns of runout on the bench check. At that time our spec. was 15 microns maximum. The result was a HUGE variation (80 microns from memory) between the bench check and the completed vehicle check. We then took ~20 of the cars with the worst case runout and performed torque test (torque pattern, torque increments, etc.) a saw HUGE differences again. Aluminum wheels acted different than steel wheels, etc.

We installed some on-line equipment to phase the rotor and hub assembly to to best phasing. We began hourly checks of the automated lug nut torque equipment. We changed the spec. from 15 to 10 microns for the rotors and from 30 microns for the rotor and hub subassembly to 20 microns. We changed the design of some of the wheels to create a more uniform clamp load.

All of these things in combination greatly reduced customer complaints.

Another interesting bit of information that came out of this study is that if the rotor had a "prime number" (i.e. 31, 37, 41, etc.) of cooling fins it reduced brake noise and brake jutter. Also, if a current was applied to the rotor during machining (a patented process developed by our rotor supplier) it changed the resonant frequency of the rotor and reduced brake noise and brake judder.

One additional thing I just remembered. The residual stresses in the rotor imposed by the casting process causes the rotors to "grow" at different rates when they begin to get hot. We changed the mold cavities to achieve a more uniform cooliing rate. BTW, we discovered that Brembo does an excellent job of controlling residual stresses and even used the Brembo rotors as service parts for a short period.

I hope this helps.

Regards,

Greenlight

 

[trailingwire]

frankee of course overtighening the wheel will distort the rotor and cause it to run with a side to side wobble and cause a brake vibration when applued

 

[Pressed]

Can a brake rotor warp from over-tightening a tire and rim? If the rotor is over-tightened? Maybe, I would think it based on amount of abuse and the configuration.

I visited ORNL and they have been studying brake rotors for a while. One gleen of info they said for rotor failures they had studied was not to combine these two activities: Similar to driving in rolling stop-n-go traffic where you keep your foot on the brake applying pressure but still moving, followed by high speed and pressing the brakes two times or more. They had some failures and had to explain why, I should have more definitions but it's been four years. Here's the links:

http://www.ms.ornl.gov/htmlhome/rsuc/rotor.html

http://www.ms.ornl.gov/htmlhome/tpuc/ircamera_apps.html

_______________________________________
Feeling frisky.........

http://www.tailofthedragon.com

 

[IceStationZebra]

I had a situation where a 16" x 6" heavy off-road brake drum was distorted which caused very severe brake pulsing. The cause was a hub extension for duals that was clamped on the outboard side of the wheel with the wheel studs, that wasn't square and pulled all of the studs <1deg in the same direction.

I can believe that overtorquing certain wheel designs would result in disc distortion.

 

[Metalguy]

Correct me if I'm wrong, but I'd think that a drake disc would be far more likely to cause pulsations if it varied in thickness rather than lateral runout. Since most calipers float, wouldn't the entire caliper simple wiggle back and forth with any runout? It can't do this if the thickness varied, so you'd feel the hydraulic pressure effect in the brake pedal-which is what happens in my 1988 Toyota Supra Turbo.

 

[modistran]

Using a torque wrench is the only way to properly tighten the wheel lugs. Tire shops use the torque sticks that get close but are not perfect. Un-even tighting of the wheels will cause much more warpage. Mechanic tightens first lug with impact-let's say 1oo ft.lbs.,then he blast's away at the opposite lug at the same torque. He now has the first lug much tighter because of the bending effect. I was taught many years ago when I was working on Bmw's to use the torque wrench. Years ago when the brake rotors were massive you could blast away. Get the torque wrench, dust it off and give your customers what they deserve.

 

[Metalguy]

Torque wrenches may be better than "mechanics judgement", but they can be very error-prone. They are not generally used for critical applications. Friction effects are the culprit.

 

[GregLocock]

Metalguy, "Correct me if I'm wrong"

OK!

What happens is that the rotor wears as the pads skim the high points, so it develops a thickness variation as a result of the runout. One solution is to use a particular pad material that grinds off the high spots

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[wildboar]

FAO Greenlight.

I am very interested in the statement you made below.Can you expand on the method of applying current during machining and how (and how much) the resonant frequency changes.Any info links etc would be greatly appreciated.
Thanks in advance.


"Also, if a current was applied to the rotor during machining (a patented process developed by our rotor supplier) it changed the resonant frequency of the rotor and reduced brake noise and brake judder."

 

[Greenlight]

I don't know all of the details of the process. I do know that when you struck the rotor with a hammer the rotor with the new process (current applied during machining) had a dull thud and the standard rotor had a high pitched ring.

I also know that they stumbled on this because the machining equipment had an internal short that caused the current to be applied.

Try researching patents at

http://www.USPTO

.

We ran several rotors on a brake dyno and the results were extremely significant in reducing brake squeal and less significant (but still effective) in reducing brake "jutter". We tried several different brake pad materials and it worked with all of them.

 

[wildboar]

Greenlight

Thanks for that.It sounds like somehow the natural frequencies were lowered as a result of the application of current.I will try and find more detail.Thanks for your reply and if you get any more info it would be great if you could let me know.

Cheers
W

 

[wildboar]

FAO Greenlight

Can you say which Japanese Motor manufacturer you worked for and can you confirm if the rotors machined using the new (increased damping) method actually went into production or was just a test/development idea which went no further.Thanks.

W