Here is a thread from a forum where somebody asked same question:
I have a 1989 445C industrial. When traveling on the road, the tractor drifts slowly to the right, requiring an occasional left turn input to drive straight. Otherwise the power steering works well in both directions and with heavy loads in the bucket. I realize that with hydrostatic power steering, the steering wheel is not directly attached to the tie rods.
Is there any cause for concern with this?
Thanks:
Re: Hydrostatic steering drift? in reply to UPFord, 03-25-2017 14:33:28
Sounds like every hydrostatic steer tractor I've driven. Some are worse than others.
My experience - we bought our first tractor with hydrostatic power steering in 1963, a International 806. It drifted. After graduating with Mechanical Engineering degree, I worked for Allis-Chalmers, Case International, and Caterpillar, from engineer to engineering manager. The only machine without hydrostatic steering drift was a special one with separate front and rear steering. It could not tolerate any drift. I needed the supplier to design a special control unit with zero leaks checks. Cost was roughly 4 times that of a standard unit.
Through the hundreds of machines from those 3 manufacturers I’ve driven, some have almost zero drift while others are noticeable enough for a person to demand changing it out. Remember now, I was working for companies and changing a unit out, especially a test unit I would be operating, was less expensive than downtime to tweak a unit. It would be swap out and return to supplier for analysis. I’ve been retired 12 years and I cannot recall failure analysis or how many steering wheel turns per mile to compensate drift were considered excessive. That is how I recall measuring drift - turns per unit distance traveled. Especially easy to track if you have a spinner on your steering wheel.