2003 Ford Taurus

Brakes problem
2003 Ford Taurus 6 cyl Front Wheel Drive Automatic 95000 miles

When I apply the brakes there is a shimmy in the steering wheel. I have had the tires balanced and the rotors replaced and resurfaced with no luck. The strange part is that it doesn't always shimmy. At times when I drive the car it brakes smooth and straight, other times when the brakes are applied lightly it shimmy's quite hard but other times when the brakes are applied a little firmer the seem fine.
what causes this? I'm thinking a proportioning valve but I'm shooting in the dark.
August 21, 2009.

Have the front end check
inner and outer tie rod ends
one is bad if not both
most common is the inner and some times it is very hard to detect

Aug 21, 2009.
Thanks for the feedback. Would I see uneven tire wear from bad tie rod ends?

Aug 24, 2009.