Hey guys, I'm sure you've heard this problem plenty of times, however sadly google can't save me today!

First off, I'm quite new to Maya, so sorry in advance.

Anyway the problem is, I have a wheel rig on a car that rotate when the car's master control moves. All is good, it works, but only when you translate the Z axis. When I turn the car model and then 'translate' the direction the car is facing, the wheels will not move. Can someone tell me what to perhaps type in the expression editor? I followed Lynda.com's tutorial, but yet this problem persues. Attached is an image of the Expression editor. "Control_FR, BR" etc being each of the nurbs curves on the wheels, "Control Master" Being the main parent to move the car.