In Reply to: CTS - mud hog posted by Ron on September 16, 1997 at 21:29:38 EDT:

the problem you are experiencing is common in
rear wheel assist combines. the oil in your
hydrostat is going to the rear wheels instead
of the fronts because the oil flow is directed
to the rears when the fronts are bogged down.
so naturally the rear wheels will spin, especially
if you have wide tires in the front.