My friend's Caterpillar D4 dozer main clutch started slipping recently, it was unable to climb a slope or pull a load. We tried adjusting it but something didn't feel right so we stripped it down and found the problem.
Check out Pacific Northwest hillbilly's restoration of a similar d4 dozer - https://youtube.com/playlist?list=PLkzQBXOwxGo_DZVRcJsvQ2qsB0rQOpH87
My other channel (Angry Ram) - https://www.youtube.com/watch?v=vIjTxxD3M4U&t=47s