Make sure the car isnt running, sit it in your lap. Turn the wheel from left to right (or have someone else do it) while watching the linkage. Maek sure nothing is in a bind, and their is nothing in your wheels etc.
Sometimes things bend you can't easily notice without a up close look.
If nothing is in a bind, unhook the linkage from the servo. Again have somone turn the controller while you watch. It is poissible that the servo is worn, or broken.
So check linkage. If ok
remove linkage check servo.
Check wires make sure they are in good shape and not grounding out.
Check batteries in transmitter
Try to narrow it down, peice by peice and find the culprit. I once had a peice of gravel inside my wheel, i took apart the whole damned buggy before I found out the gravel was binding the tire, not the servo or the linkage.. go figure..
Their are also several site on the web that tell you how to rebuild a servo do a google search and see what turns up.
Also when posting for help try to include as much info as possible, what car you have, radio, and servo's it helps to diagnose
