How do I diagnose a won't lift problem with David Brown 990 Hydraulic lift?

Ash, thank you for the help. The tractor has a white hood and three gear shifters on the top of the transmission. I found the dipstick, the oil level is quite low and looks a bit milky. Now I am having trouble finding where to add the transmission/hydraulic oil.

Steve
February 2011

Steve you don`t say weather your 990 is a implematic or a selectamatic (red or White). The hydraulic oil and the transmission oil is all the same reservoir on both models. The hydralic systems however are very different. The dipstick is located on top of the transmission cover (non cab) versions. Selectamatic Q cabs had a sight glass on the left side of the transmission case.
Check the oil for water contamination, common fault if left outside on non cab tractors.
Fault finding is more model dependent as to why it will not lift.

Ash
February 2011