OK some discussion has taken place regarding the axles in these things, and their survivability behind more powerful engines. Let's take a look.
The front axle is rated for 935 lb-ft of torque.
The rear axle is rated for 1,450 lb-ft.
Divide these ratings by the combined low gears of the transmission and transfer case, to get a worst-case value. Transmission 1st [6.398] X transfer case low range [1.96] gives us a multiplication factor of 12.54. This 12.54 x axle gear ration =
crawl ratio, or 73.6098:1, but that's not important in this discussion.
Then, the stock engine is rated at 191 net lb-ft of torque. So in high range (Transfer case) and 4th gear, the axles would see a total of 191 lb-ft of torque. Child's play. Now, multiply the 191 by the factor above [12.54], and we see that the axles then receive 2,395.14 lb-ft. WOW! If we suspect that the front axle will do 39% of the work, and the rear does 61%, we see that the front receives 934 lb-ft (rated at 935) and the rear receives 1,461 lb-ft (rated at 1,450), and we clearly see that the axles are right up against their design limits in low-low, with the original engine (when operated at the most extreme end of the vehicle's capabilities)! Then you get into the situations of shock loading where spinning tires suddenly find traction? Ugliness may soon follow.
Naturally, there are other factors to consider. The degree of "go-pedal" used, state of tune of the engine, and perhaps more importantly, does one ever stress the truck to the point of stalling the engine in low-low at WOT? I did in a truck pull, may not again after seeing these numbers!
Is it any wonder that these axles CAN fail when the truck is repowered with an engine that produces two to three times the torque of the 1bbl Tornado?
Now, I'm a big fan of these trucks. I applaud those who wheel them, resore them and modify them. I'm NOT slamming these trucks. At all. This is just a posting of the results of my study of the manuals here on-line.
Makes a bit of sense now to keep the itty-bity u-joints, huh? Easier and cheaper to change than an axle!
Food for thought.
Bob