Since we already have Rusty's resume, here's my short version. I don't have as much HD truck experience, but I think more experience "pushing it" with oversize tires. Long time 4x4 breaker of axles, etc., mine and other's. Run a large machine and welding shop where we fix or make any and all kind of broken stuff all day...including heavy trucks. Been around M35's converted to civvy water trucks (own two) and talked to guys that ran them back in the day. They run way overloaded (frames reinforced) and what breaks is spiders and axle shafts. Mostly in the rear, haven't come across front breakage yet. A buddy runs 395s and 6wheels it pretty hard, it chewed up the spiders in the middle axle. I think this is from cresting sharp ledges where all the weight and traction goes to the middle axle. 395s are pushing it for M35 axles, though maybe not in a 4x4 setup. If you want to run 395s "unbreakably", I think you need to go 5ton axles, which are heeeeaaavy. Maybe talk to some of the guys that build rockwells for mud trucks, like Red Barn Customs.
I remembered I once blew the 1410 series (same as M35) driveline yoke off the front of the D80. Cummins, 4lo manual trans with an F350 hanging off the back, got hung up on a VW sized boulder and I didn't get to the clutch in time.
All heavy duty axles have full floating shafts, none of them are going to let the wheels fall off.
D80s and M35 axles have about the same dia shaft, but the steering ujoints, steering knuckles, and housings are much heavier on the rockwells.
Breaking drivetrain parts is a relation between power (torque and/or shock load), weight, and traction. You can put a lot more power to something with bigger tires if you take the weight off. Diesel engines that are used in medium duty trucks are often derated or detuned from the pickup truck config as they pull more weight and will break or prematurely wear powertrain components if turned up.
. But I suspect God doesn't know much more about heavy trucks. I always enjoy his post.
