Have this early 4030 quad range, tractor had a lot of transmission issues. Entire 8 speed has been rebuilt, the two speed assembly checked out ok .... however get tractor together and two speed will not work. Took valve housing off left side and tested the shift action with air pressure, it will make the shift that way. New o rings on adapters and don't hear any leakage getting by. Swapped out housing with another and still no go. According to gauge we have 110 psi of pressure at the clutch port. All other hydraulic functions work ok. I added two more shims to the pressure valve, still no go on the 2 speed. Any ideas?