Tires: vibration when braking at high speed, goodyear aquatread, ford taurus

Question
Mr. Smith:

I have a 2000 Ford Taurus with alloy wheels.  I purchased new Goodyear Aquatread II tires about 14 months ago.  About 2 months ago, I noticed that the car shakes when I applied the brakes at highway speeds (over 55 mph - it is not noticeable at speeds below 50).  

A few weeks later, I took the car to the tire dealer where I bought the tires and had them rotated and balanced.  It seemed to help at first, but now (another few weeks later) it seems to be even worse than before.

Could this be due to faulty balance by the tire shop?  Are there other causes of such problems?  

It rides smooth at all speeds if I don't touch the brakes.  Even moderate brake pressure causes some pretty serious shaking in the steering wheel when traveling over 55 mph.

I plan on taking it back and asking them to rebalance the tires.  Any other information you can provide will be greatly appreciated.

Regards,

Tyler Harris

Answer
Tyler,

What you have is warped rotors.  See if you don't feel a bit of pulsation in your foot when the vibration starts.

It is caused by the heat that is made between the rotor and the brake pad causing uneven stresses in the rotor.  Thin rotors and hevay brake usage aggravates the situation.

The fix is to get your rotors turned.  Rotors have a minimum thickness, so they may need to be replaced.

I've got a 1998 Taurus and if I drive through the mountains, I develop a vibration when ever I use the brake pretty hard.  In my case the vibration is temporary and normal flatland driving doesn't make this occur.

Hope this helps.