Hook: There is a small difference in front-rear traction speed - the front tires try to cover more ground than the rear ones (true for most 4-wheel-drives). For this reason there is almost always some extra contact force in the gearing when in 4wd making it hard to pull the lever out, and occasionally some mismatch preventing it from going in.
Engaging or disengaging 4wd is always easier on non-paved surfaces. Dry pavement makes taking it out of 4wd a real bear. A good trick when it's doing this is to turn the front wheels sharp left or right and change direction - as you start to move either forward or back keep your hand on the lever and you'll feel it just slip out easily as the mismatch in gear speed crosses over the zero point.
This problem varies depending on tractor model, tire type (R1 or R4 etc.), inflation, tire wear, and anything else that affects tire diameter - like a load in the FEL. With a heavy load in the bucket, no weight on the 3ph, my tractor shifts in and out of 4wd easily goind straight on dry pavement. But with an implement on the back, or less load up front, its a lttle different, maybe coming out hard unless turning or changing direction.
