Why did it die?
What caused The Carnage to our Avalanche? Our theory starts when the torque of the engine and weight of the vehicle broke one of the original engine mounts on Ultimate Adventure. This was partly due to the OEM engine mounts having no mechanical lock built in, but rather just two pieces of metal bonded to a rubber mount. It also didn't help that we had no crossmember under the engine when we did the solid axle swap. Off Road Unlimited offers one, but we felt it was fine without it since we weren't building an extremely tall truck. On the trail we broke an engine mount, so we put a new one in that was modified by drilling and installing a bolt to give it a positive mechanical lock should the rubber fail.
We also added a tube crossmember while at Off Road Connection in Alabama. Unfortunately, we think that the four bolts holding the adapter to the back of the transmission were already rounding out the threaded holes in the back of the tranny by this time. So even when we removed the transfer case and retightened them in Pennsylvania after the trip, it was only a matter of time before those bolts loosened up again. Lucky for us, that time came along the highway in West Nowhere, Iowa, at midnight.
Imagine the transfer case slowly sliding off the transmission until it binds the rear CV at 70 mph. This could cause the case to be torn apart and The Carnage to begin. The rear driveshaft was spinning so fast that it beat the bottom of the truck a few times before hitting the pavement and turning parallel to the axle. At this moment the driveshaft could have become jammed under the right rear tire, and for a millisecond the tire and ring gear could have stopped before tearing the pinion yoke apart and sending the shaft off into the tall grass along the Interstate.
This catastrophic event could have been the root of the first ring gear losing some teeth and the rear axleshafts twisting at the splines. There is a lot of force when a 9,000-pound truck is barreling down the highway.
This is, of course, all speculation and theory, and most of our changes since then have had a positive result. The new transfer-case mount and engine mount seem to be holding everything together just fine now, and the crossmember, springs, and traction bar are all helping strengthen the frame and suspension for when we are twisted up. The new axle and driveshafts are also holding up to the abuse of some serious off-roading (Moab and Johnson Valley), and we'll see if we break any more gears. We've decided that wheeling a fullsize truck on tight, narrow, off-camber, steep, and rocky trails is a blast. It breaks stuff, but it's all in the name of research.