Gentlemen: Can someone please help identify the brake shimmy I felt while canyon bashing this weekend. I did some fairly hard driving but not excessive braking up a local canyon and about half way up the canyon there was a small but noticable shimmy when braking. After clearing the canyon, shimmy was gone. Is this strickly heat issue or do I have a bad rotor. I had no fade or feeling of loss of braking just this annoying shimmy. Only 6800 miles on car. Also I have the x-73, which by the way makes an incredible difference running the same canyon. Car is on rails now compared to run without. Thanks for the help. Fish

 

I doubt it's your rotor.

At what level of braking did it occur? And you can't reproduce it now?

 

Fish, Try STOPTECH's website. They have a lot of good info under their FAQs link. Here's one on "Warped" rotors. STOPTECH
-Glen

 

Dock: It occured both on way up the canyon and down the canyon about 24 hrs apart. Once the car was warmed up with some hard braking it started. Definitely felt it in the steering wheel. I tried to reproduce today with some hard braking but was not able to achieve. My only conclusion is that the heat is causing something, yet no fade just shimmy! Any experts to chime in? Fish

 

Shimmy sounds like warping of a rotor when it gets hot.
Fade would only happen if the brake fluid got too hot,
like on a race track.
*Something* is going out-of-round/warped due to
brake heat. Get your rotors examined.
Joe

 

joe is right on. it is heat induced warping of the front rotor. it only occurs on application of the brakes and after they heat up and you feel it in the steering wheel when it is the fronts. Get it checked for tolerance.

 

Did you read the "STOPTECH" link in Dr. T's post?

 

Thanks, I did read the article but I might as well have the rotors and pads checked. Something is definitely not right. Fish

 

Fish - I've just experienced the exact same thing - only under excessively hard braking after running hard on country lanes for a while - after things "cool down", the vibration goes away (i.e. in daily driving). I too will have my rotors checked.

I'm starting to lose faith in my car.

 

I was wondering if james had read the article.

 

It's probebly an irregular buildup of pad material on the rotor that later wore off.

 

Or perhaps calipers sticking. I don't know how they are designed, but just food for thought. Perhaps with big heat, it somewhat locks up, and the floating calipers just don't float anymore.

Irregular melted pad wouldn't go away on its own, and unless it was really bad, the steering wheel wouldn't shake, imo.

 

Could also be your pads getting **** bedded on to the rotors. I've had that happen.... Does it vibrate whilst driving?

 

Dock, thanks for the heads up. I really enjoyed the article.
Dock, the "warping" issue is one of semantics. Cementite and deposits of pads on the rotors is synonymous with "heat induced warping." The actual metal of the rotor is not "warped" and everyone knows this b/c the rotor is still spinning when not braking and yet the shimmy is not felt. It is only upon squeezing the rotor that the resonance is produced b/c it then hits the pads and there is variable friction from the heat induced irregularities. It is not correct to determine cracking from the cross drills as the problem (unless a lot of the cross drills connect the dots) or actual twisting of the rotor out of alignment unless it or the hat is mounted wrong.

This is why the rotor needs to checked out #1 make sure it is mounted correctly and #2 see if there are deposits and irregularities on the surface and almost always, the clue is on the surface of the pads rather than the rotor. If you have eye loops or a strong magnifying lens, looking at the pads and the rotor surfaces before and after hard braking can be quite an experience. That is why when I track I switch to Padget orange and bed them properly and when i go back on the street it is the stock pads rebedded. My dealership mechanic and I decided that the rotors could tolerate the appropriate heat sensitive pad for the track and change back to stocks. All of my "heat warping" went away. I suppose it is an expression that should have been dropped a long time ago but in race circles the term is still used but not to mean a deformation of the rotor but rather a build up onto the rotor that makes it shimmy UNDER BRAKING not while accelerating. Sorry for the confusion.