Any help greatly appreciated. Both tracks pull fine forward and backwards. The left brake still works but the left clutch won't disengage. I removed the steering control valve and disassembled but didn't notice any visible issues but I really don't know what to look for. There appears to be very few parts in the valve to fail but I may be overlooking something???
Perhaps the clutch disks are frozen to the plates. Howard
Did this happen suddenly while it was running, or was it like this when you started it up? If it was stuck when you started it up, Hetkind is almost certainly right. D21s have dry steering clutches, and are famous for this problem. You can usually break it loose by pulling the left steering clutch back until just before the brake applies, and driving the stuffing out of it. get it good and hot and run into things, run that track into stumps and logs and whatever else you find. Basically, just abuse the poor little thing half to death. You are trying to shock load that clutch, while holding it disengaged. If this doesn't work, you'll have to replace this clutch.