I came across this while looking for something else. The Hydrashift unit is a actually quite simple as mechanical things go. (the 3 point linkage hydraulics are actually more complicated than the gearbox hydraulics.) As someone else commented just take your time, double check if something is tight and don’t force anything and you will be fine, taking this apart. Mechanically this gearbox is actually very strong, it was massively overdesigned for the horsepower that originally went through it when launched. The hydraulics are simple and the valve setting can be done with a grease gun filled with oil. In principle how the gearbox works is it has 2 x epicyclic units, with a clutch pack inside each epicyclic unit. 1st gear is both units are in mechanical drive through the epicyclic, no hydraulics, are needed, and that’s what the brake band does. It locks the epicyclic hub from turning. This means it always has engine braking and wont run away on a slope, and you can tow the tractor to start it. When 2nd gear is selected the front clutch pack locks up and front brake band releases, and the rear unit continues to drive through the epicyclic with the brake band locked on. When you select 3rd the 2 epicyclic units swap, the rear unit clutch locks up, and the rear brake band releases, with the front unit going back to epicyclic and locked. For 4th gear the front unit clutch engages and both brake bands are off. The hydraulic pump for the gearbox is driven off the gearbox. This means that each time the tractor stops the hyd pump stops. Which is why it goes back to 1st gear. Other than contamination in a valve the only thing that really ever goes wrong is if someone thinks its automatic and leaves it in 4th, because the clutches can slip engaging 3rd gear because there is not enough oil flow to work the clutch pack swap over. Most of the units I repaired where ones which other people had tried to repair and upset the settings, there was nothing much major wrong. But it is a “cab off, and gearbox lid off to get at the parts to do the settings