He was trying to climb an optional line near the end of Gold Bar Rim that I had just seen a couple jeeps try and fail. He started out in 4 hi (TOD) for whatever reason then switched to 4 lo. I doubt that switching is what caused it, it was the additional torque of the low range more likely. I never knew the TOD cases were chain driven. Think thats what popped. Cece has video of when it happened. You can hear it pop, it was loud. I thought for sure it was a CV since it sounded exactly like one.