Never broke a knuckle but I do carry two in the equipment box on my trailer. I have broken steering studs, trunnion bearings and Birfields. These were all fixed on the trail where I broke. If you break a birfield or trunnion bearings, fix ASAP because it can and has locked up steering. If you blow a Birfield and do not have a spare (Just because you are running Longfields does not mean they will not break) pull it out, clean it out, shove a rag or paper towel in the hole, this will slow the diff lube from leaking out. Run in 2-wheel drive as much as possible (that is when a twin-stick comes in hand, low gears 2-wheel drive.
I came out of 4-dice in 1-wheel drive once, I blew a rear axle and a bit later I blew both sides of a Birfield eliminator kit, front R&P and a hub. with a little strapping and winching I made it out.
