May sound like a dumb question but my 92 Accord Waggon, like many others on this forum, shudders badly under braking and appears to have a slight vibration at speed. I'm planning to replace the rotors tomorrow but upon visual inspection, when I turn the rotors by hand, I don't see any evidence of warping. I'd sure hate to replace the rotors in vain.

So far, I've had the tires rotated and balanced, and I've replaced the struts, outer tie rod ends, and ball joints. No unven tire wear.

I've read in other posts, about the importance of torqueing the lug nuts, which sounds intriguing. I might try that first.

Anyhow, I'd appreciate your thoughts on my original question.

 

Rotors do not warp. There is no linear grain that can cause the rotor to warp or twist like a piece of wood.

What would cause the pulsing or shudder of brakes is from an uneven transfer of pad material to the rotor, from an incorrect bed-in of the pads. This can become worse if not corrected, the uneven areas if overheated can actually change the rotor material in the hot spots from grey cast iron into cementite. This cannot be fixed or machined as it changes the composition of the material, the only fix is rotor replacement.

A rotor that was not machined correctly or through uneven pad material deposits can cause machining of the rotor. This will occur with more aggressive pad materials.

When the rotor gets near the end of its service life it will not be able to dissipate the heat quickly enough. The sections of rotor that are above the hollow veins will collapse from the heat and pressure. This is why rotors have a minimum thickness. Cheaper rotors that do not provide enough material the discs thickness itself, sometimes called 'light weight', these rotors will have the stock overall dimesions, but the thicnkess of the rotor wear area is actually thinner. The cooling veins tend to be larger, this is often advertised as an 'advantage'. It's just a way to save on material, and has all the downsides.

Usually there may not be any witness marks on the rotor form differences in thickness in the rotor unless the rotor has an uneven transfer of pad material and the rotors have been overheated causing bluing on the hot spots. But if the rotor is simply out of service life, then you will not see anything.


This would not affect the 90-97 Accord front end. Reason is the rotor is behind the hub. The wheel is mounted directly to the hub, the rotor is not sandwiched between the hub and wheel. In the more common Rotor Over Hub design, over torquing could cause the rotor to be distorted from over-torquing the lug nuts. As the rotor is squeezed it may distort from the excess pressure. But with the factory front Hub over Rotor design on the 90-97 Accords this would not be an issue. But it could affect the rear.

 

Thanks. I did a little more reading after seeing your post and thought this was a pretty good article:

http://www.stoptech.com/technical-su...nd-other-myths

 

New rotors cured the problem. Actually, they're not quite new. I took a chance and pulled two hub assemblies off an Accord at the wrecking yard, for $35 apiece. Easier and cheaper than doing the presswork, but risky. If you put the new side by side with the old, you wouldn't see any difference. Amazing.

I decided to use the pads from the donor car. Seems like the car has less stopping power than before, but it's hard to tell, with the way it used to shudder.

 

If you read the other links from StopTech(Centric) check out the bed in procedure as well. It may just be your new to you rotors/pads just need to be bed in.

 

Great reply!!