My 04 RX vibrates like crazy at high speed braking. About a year ago, rear rotors were replaced but fronts were machined. How can I tell which front rotor to replace? Or do I need to replace both?

Sewell does not seem to sell the 04 models. Any other reputable places for the rotors?

TIA.

 

It is best to replace them as a pair. Change both pads as well. Look here:

http://brakeperformance.com/

 

I would replace the front rotors. The rear brakes provide only 30 percent of the braking for your vehicle, so the problem is most probably the front rotors.
I noticed that you are in Ontario. I would recommend KVR brakes, they are in Ottawa. Wonderful company to deal with plus the brakes are great.
URL: http://www.kvrperformance.com/

good luck

 

Check the control arm and ball joints. These could cause vibrates when you brake.

 

Don't know if you ever got this fixed, but warped front rotors will shake the steering wheel when braking, and warped rear rotors you will feel the vibrations in your seat (butt) when braking.