4100 HST Steering Problem

[cheesemanmax]

It's been a long time but, I'm still a proud JD owner. Here is my problem, plowing snow yesterday my steering started to get difficult to turn. I did not muscle it instead kept consistent pressure on the wheel and would continue the turn. Well I was ready to pull into the garage and the steering stopped working. I could turn the wheel without the tires turning. I pulled into the garage and removed the ball joint from the steering. Started the tractor, on idle I can turn the wheel and the cylinder will move. When the cylinder reached full in or out the steering wheel will continue to rotate. All of the other hydraulics seem to work fine, plow in all direction, forward reverse and 3pt. I drained the fluid, removed the screen and filter. The fluid was clear to start but turned milky about half way through the draining. I did not find anything questionable on the screen only grit on the magnets. I plan to replace the fluid and filter.

If the fluid and filter do not work, any ideas? I like do do my own work but, understand I may be over my head or not have the required testing equipment.

Thanks for any help!!