Krone Tedder Wheels Won't Run Straight

Hello everybody and hope all is well.  I picked up a 2004 Krone 5.50/4x7t four basket tedder last week and had the chance to use it for the first time today.  Everything works fine with it, except the wheels won't run straight....When being pulled the thing yaws to the left and right.

 

This tedder has a feature that allows the wheels to be angled to the left or right (to clear field boundaries according the manual). I have the angling lever set so the wheels run straight, but as you travel down the field, the wheels swivel to the left and right which causes the tedder to swing to the left and right.  I've checked to see if there is a way to lock the wheels in the straight position, but have had no joy. 

 

Has anybody else ever encountered this problem?  Any idea on how to remedy it?  Could it be something as simple as tire pressure being too high?  (I'll have to test that theory tomorrow).  

 

Thanks,

Chris

Krone Tedder Wheels Won't Run Straight