I work at a volvo dealer and a customer brought in a 1840 case skid steer. I let it warm up for about 20min and then drove it around about 5min after driving the right side drive started failing. I could push both sticks forward and it would go straight but turning with the right drive was not an option not really familiar with this piece of equipment any help would be greatly appreciated!
First check all linkages to the top of the big pump under the seat, make sure you are getting proper motion in both directions with the control lever, this problem can be caused by a number of issues including broken bolts at the pump mounting plate to just worn bearings on the linkages themselves. But once its working for a period before it starts failing then it most likely the tandem pump under the seat, when the hyd oil gets hot the pump leaks causing the problem you've described, it can also be the drive motor (less likely) but to narrow it down just swap the hoses and see if the problem switches sides(if it does, the tandem pump if it does not the motor). To be sure and to make it look good you can also perform these pressure tests...
Pressure tests at tandem pump under the seat. View attachment 1840,1845C tests p2.pdf View attachment 1840,1845C tests p1.pdf