Hib Halverson

As for the brake rotor issue: 1) the problem is not caused by driving through puddles and 2) machining or cutting the rotors is, sometimes, a wasted effort.

In many cases the problem is actual warpage. It's more likely poor quality cast iron which develops "hard spots" or cementite. When this happens the rotor surface develops inconsistent friction under braking. That results in a brake shudder but, in that case, the shudder is not a axial vibration caused by warpage, it's a rapid fluctuation in deceleration rate. This can be most obvious if you are braking moderately and hold even pedal pressure. Just before the car comes to a stop the frequency of the shudder slows to the point that you can actually feel the decel. fluctuation as a back-and-forth motion.

The reason that machining the rotors doesn't make a difference with that type of problem is 1) since the problem is cause by heat cycling, when you remove material from the rotor during the rotor turning process you make the rotor less massive and more susceptible to hard spotting and 2) Sometimes the depth of the hard spots is more than the depth of material removed during the machining process.

If you have brake shudder, measure the rotors for warpage and thickness variation. If those characteristics are within specs then the shudder is probably not a result of any warpage.

The solution is new rotors made of higher quality cast iron.

There is a very interesting article about this problem of cementite deposits on rotors on the web site run by Stoptech, an aftermarket brake parts supplier.