If you look at the top of the valve there are two plugs. As I recall it is the plug that faces the front of the tractor, the other will align with the bottom plug for the spool. I will add that oil pressure it makes a big difference who those tractors steer. So I would start with getting some gauges connected and see what you have. I bought a ST280 little over a year ago and you could hardly steer it. Really did not think it would be that big a deal to fix and it was not with the exception it had more than one issue. While the pump on this tractor still worked when it was made the outlet port was a little to close to the rear bearing and it cracked into the bearing so oil was able to recycle around in the pump so flow was down some. Main pressure relief was suppose to relieve at 2250 psi. It would start dumping at 1800 and 2000 psi was all the higher it would go. When those two issues were resolved than the steering pressure relief showed it was low. As I mentioned last night you could adjust it but the setting would not stay. Replacing that valve solved that issue. 

I do have the service manual and parts book so if you need more help I would be happy to share the information that I have. Email in profile is good and check everyday. Email with phone number and will be happy to bring the manuals home and talk to you.

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