How to diagnose a warpinG rotor?

[Arnold]

Fine when cold. UGLY :!: when warm..as in check this out NOW BEFORE driving it again. Came on fairly suddenly..as in WTF IS THAT? Rear rotor on my truck. Pulled both rotors..looked ok..put it back together..same. Pulled them again..flat..even touched them up with a grinder. Put it back together. Same. Got me thinking maybe a caliper grabbing when hot..(been there) plus something else loose. I dunno. About the only option left was to put it up and drag the brake..either someone else..or load the pedal a bit..then looksee for runout when warm. Seemed easier/quicker dirtier to just "throw parts at it". In this case a rotor.
I threw a rotor at it and lucked out. Both rotors looked the same..I just had to guess. Problem solved. I still..looking at the rotor can't believe that it was so good cold..and just so ugly when warm..not even hot. Just as soon as it warmed up.

Maybe mount up some digital runout mic. with a tone feature on it and drive it

[enjenjo]

Overheating it once will ruin it forever. Once it warps, it may come back when cold, but will easily distort with just a little heat. Even turning it won't cure it.

[Arnold]

Overheating it once will ruin it forever. Once it warps, it may come back when cold, but will easily distort with just a little heat. Even turning it won't cure it.

Thank You I did not know that :oops: I thought once a rotor warped that was that. I had never heard of one that came back when cold.

In this case this rotor was NOT overheated in the last 3 years. Before that..ya..I got it pretty hot but it was fun
I had 3 years of  normal use out of it since then

Before that I DOUBT very much whether the previous owner EVER overheated it (former Police cruiser with H/O engine)

[UGLY OLDS]

Gee ...How hot could the rotors get in the donut shop parking lot  :?:  :?:  Unless maybe they spilled coffee on them...  

Bob....

[GPster]

Did you change the wheels size/type? In 1999 (?) we bought a new Jeep Cherokee and they had supposedly changed the design/part in the front brakes and we had a warping problem with the front rotors. They said that it was a design/materal "Fluke" and they tried turning the rotors at 6,000 miles. They replaced the rotors at 11,000 miles and when we traded it at 31,000 miles it needed something done again. This was before I started driving again and we didn't have any problems with brakes with my wife's driving on our previous '93 or '96. A 2003 showed the same problem that got rectified and after that we bought one that went 135,00o miles with-out any brake problems. By then they had increased the wheel size from 15" so that there was more breathing room around the rotors. GPster

[Arnold]

Did you change the wheels size/type? In 1999 (?) we bought a new Jeep Cherokee and they had supposedly changed the design/part in the front brakes and we had a warping problem with the front rotors. They said that it was a design/materal "Fluke" and they tried turning the rotors at 6,000 miles. They replaced the rotors at 11,000 miles and when we traded it at 31,000 miles it needed something done again. This was before I started driving again and we didn't have any problems with brakes with my wife's driving on our previous '93 or '96. A 2003 showed the same problem that got rectified and after that we bought one that went 135,00o miles with-out any brake problems. By then they had increased the wheel size from 15" so that there was more breathing room around the rotors. GPster

 Thanks..no I did not change the wheels. I did change the pads to a different type. That seriously overheated the calipers and destroyed them. I had not actually ever thought about overheating calipers. Did not know there were(are now anyway) high temperature calipers). I am pretty sure at this time that I overheated the rotors too. However..it did not show. I did not use the brakes that hard again after having to deal..and figure out the overheated caliper issue. Years later the rotors are now acting stupid. That one was changed..temporarily. I just threw a cheap rotor at it and that fixed it. For now. Still have not decided on what I will go with for rotors.
  Police vehicles have pretty much always run much heavier and stronger wheels..warpage issues..heat/brake rotor heat issues. They almost always run small hub caps for extra brake cooling. The wheels on the later..2012 and on Taurus like cruisers are 2" smaller than stock..they must pass a 50mph 8" curb at 90 degrees..crash along with the rest of the suspension chassis..without significant damage.