Cause of a warped rotor?
 

My car is a 1994 SL320 with 100,000+ miles.

Recently I have developed a pulsating thumping noise coming from the left front wheel. A local INDY diagnosed the problem as a warped left front rotor. The rotor is OEM and has never been resurfaced. A brake inspection 2500 miles ago indicated everything was OK. Pads appear to be good for another 10,000 miles. Does anyone know the cause of a warped rotor? Lugs not properly torqued? What is the correct torque? Excessive heat on front rotors? I drive like an old lady. It seems like the problem is always with the front rotors. I have never heard of a warped rear rotor.

Thanks in advance,

Scott - rnysl320

Warped rotors are common. The cause is a combination of wear, which thins the rotor, and heat due to friction. The front rotors more commonly warp since the braking system is usually designed to apply more force to the front. "Riding" the brake pedal down a long hill can get a rotor very hot. Thermal expansion and contraction of the steel rotor occurs. There are metallurgical changes that occur in steel when it is repeatedly heated (high) and cooled. Over time this causes the metal structure to be non-homogeneous, or inconsistant. Thermal expansion/contraction then could result in slight warpage. Does not take much, and you feel the pulsation. Turning or grinding the rotors "true" is a fix, but it is usually temporary, as it makes the rotor thinner, and does not change the altered metallurgical structure. I don't thing lug nut tightening will effect warpage. Replacing the rotors is the best fix.

That's a lot of miles for an original rotor. You got your money out of it.


Number 1 cause of brake rotor warping prematurely is driving with 2 feet; one on the gas and one on the brake. You see it all the time, especially on the freeway. People going 50 plus mph, but brake lights coming on often and for no apparent need to slow down. i.e. riding the brake. I guess some people may feel driving this way shortens their reaction time.

Gentlemen,
Thanks for the info. On November 1st. I will be taking my car off the road. At that time I will be replacing the rotors and installing ceramic pads. I hope the warped rotor won't damage the caliper or wheel bearing until then.

Thanks again,

Scott rnysl320

Scott;

My experience has been the major cause of your problem is over tight lugs.

1-Never let anyone use an air wrench on your wheels, usually done when you go in for inspection.

After I have my cars inspected, I drive home and loosen all the lugs and re-tighen them myself, never had a warped rotor!!! honest.

Ron

Ron,

Thanks for the info. Can you tell me the correct ft/lbs of torque? (1994 SL320). After my last inspection the lugs were tightened by an air impact wrench. If I tighten my lugs to the correct torque will the rotor straighten out? (food for thought) My local INDY seems to think that excessive heat on a worn rotor is the cause. I will be replacing the rotors soon.

Scott

I never get more than 8000 miles from new pads(organic),your pads must be too hard causing the rotor to overheat and warp.

:D it is SL320...is there any other way :laugh3:

It's the only way to drive when your older than dirt. Actually I'm quite happy with the performance. However that SL320 trunk badge makes me feel a little sheepish. Its like getting all dressed up to go out wearing my wife's shoes. I should replace it with an SL500 badge. As long as I don't punch it in the pants whose gonna know?

Scott