I went back to the C5 Forum and ran a quick search... then to Google.. Wow, lots of info on this topic!
Here are the addresses and an except from a few of the posts.
Note, when I had new tires put on the Bonnie, even though I specified hand torque... the car started to pulse when braking shortly after the replacement. I retorqued the wheels right away and the pulsing went away...
and I'm too old to smoke
Member Since: Oct 2002
NY Re: Warped Rotors (Richin Chicago)
This is the reason GM did away with the wheel locks mid-run of the C5 2002 MY. It seems the dealers, who install the locks - not the factory, were prone to using impact wrenchs when putting the locks on. This is the single biggest reason the rotors develop run-out problems.
My rotors (all 4) developed the problem after the first 3500 miles of incredibly easy-easy braking. I was stunned. They were turned by the dealer (same dealer who created the problem) under warranty (for which GM reimburses them - see a pattern here?)
I had a lengthy conversation about rotors with one the Corvette Engineers last April during the 50th AE Press Event at the Indianapolis Motor Speedway. After that conversation, I have no doubt that the run-out problems are caused by OVER or UNDER TORQUING the lug nuts.
They should be torqued in the "star pattern" three times for each wheel, 50lbs, 75lbs, and then the final 100lbs. How many "wrenches" are gonna actually do this?
Either find a good mechanic/dealer who will do this, or get yourself a torque wrench and do it yourself. Keep in mind that retorquing a wheel/rotor that already has lateral run-out will do nothing whatsoever to "fix" it. Only 'truing' or turning can fix that.
My "turrned" and properly torqued rotors have over 7000 miles on 'em and are dead-solid-perfect, even after some incredibly hard "both feet on the brake pedal" stops to check the ABS and impress friends, and myself.
Most of the aftermarket rotors that are of two-piece design (esp. floating hat types) should be fairly immune to the torque sensitivity, and thats why they seem to be "warp proof".
Originally Posted by Patches
No! They can damage your lug nuts, wheel studs, rotors or wheels. Should always tighten in 3 passes using 35, 70 and 100 ft. lbs. in a star pattern using a torque wrench.
No air tools!
I agree, I had to have my rotors replaced - they were all warped. Who do you think paid for this one?!
CF Senior Member
Member Since: Dec 2002
My Corvette Photos
Re: help with rear brakes and rotors (rons85)
Yup - rotors warp. I had that happen on my honda. Every time America'* Tire would torque the rims on - pototo chip discs. I don't let them near my car. I'll buy their tires - but I just take the rims over in the truck.
What do you mean, rotors must be torqued?
Lug nuts or wheel studs need to be tightened in a cross-pattern and to a strength recommended by the manufacturer.
Most carmakers recommend somewhere between 80 – 100 torque pounds.
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.”
Whether you’re a do-it-yourselfer or taking your vehicle to a shop, make sure this procedure is being done.
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.
Overheating can also cause rotors to warp. Overheating may be the result of severe abuse or dragging brakes. Defects in the rotor casting, such as thick and thin areas can also cause uneven cooling that leads to warpage. Hard spots in the metal due to casting impurities can be yet another cause.
Warped Rotors: More common in newer cars, but possible on all disc brake systems. Rotors warp due to being overheated or incorrect tightening of the wheel. A warped rotor will give a pulsing feeling when applying the brakes. This pulsing can be annoying and dangerous. Most newer cars have rotors which are very thin and warp very easy. Furthering the problem, the manufacturer does not leave enough material to resurface the rotor. Check with you mechanic to make sure you can safely have the rotors machined or replace with new rotors. To resurface, the rotor is placed in a lathe and a cutting tool removes a few thousandth'* of material from the braking surface. This restores the flatness of the rotor and eliminates the pulsing sensation in the pedal. Make sure when your mechanic puts everything back together that he torques the lug nuts to proper specifications and never uses an impact wrench. If the lug nuts are not tightened evenly the rotor can warp and you are back to square one. Note: Some shops use a torque stick, which attaches to an impact wrench and does not allow the torque wrench to tighten more than it should. This is acceptable. If your mechanic does not use a torque wrench or torque sticks, find another mechanic.
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'* 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.