I'd like to understand more the subject of components that suffer from torque in the drivetrain.

Let's take the main shaft of a transfercase for example - the engine is the torque provider of the system (and the only one, the others are just act in response to it)
The transmission multiplies the torque, the transfer case multiply again and last is the ring and pinion, o.k.?!
Now we all agree that if the vehicle is lifted with 4 wheels in the air there will be no twist moment in the system cause, there is no resistance to the multiplied torque of the engine.
If the vehicle is on the ground the resistance takes form by the vehicle weight and the coefficient of friction of the tire rubber.

Let's put the numbers (engine 100 lb/ft, tranny – multiply by 2.5, tranfercase multiply by 2, ring and pinion multiply by 4) ---- 100 x 2.5 x 2 x 4 = 2000 lb/ft – at the wheel.
The reaction ( the force that 'comes' back from the rear axle equal to 2000 lb/ft ) when the tires are not allowed to spin – stuck .

It seems reasonable that the rear axle 'brings' back the same torque it got because the multiplying action occurs back and forth ( slower and faster ) so the main shaft of the transfer case will suffer only 2000/4 = 500 lb/ft ?!

Now the questions –
1 – Am I right?
2 - If I'm right, way the transfer case doesn't 'bring' back the same torque it got (the
same as with the rear axle?
3 – If the reaction force is only the engine torque times the transmission, then we
have a very low load on the main shaft of the transfer case , and if that is so , why
a NP 231 will snap immediately after installation behind a V-8 and a NP 205 will
last? Certainly the 500 lb/ft of torque won't snap the NP 231 which can withstand
a 1995 lb/ft of torque ?!


Thanks in advance

Conceptually I think you've got the picture. Your example is rather lacking however, and you're using the numbers from it to compare to a real torque rating. 100 lb/ft is too anemic for any "real" V8 I know of (in decent shape). Try 400. Next is first gear; double it. My 727 has a 2.45 first, but since it's an auto add a factor of two for the torque converter. Most manual 4 speeds are in the 6:1 neigborhood and the SM420 is 7:1. 400*5=2000. If you're gonna use a real torque rating for the tcase, use a reasonable value for the applied torque.

I see what you are saying , and i was wrong - the numbers are 400 * 2.5 * 2 = 2000 lb/ft ( TH400 with a V-8 ) , but even so a NP241 or a Dana 300 should last ?!

Should be fine. My stock K1500: factory rated output 335 lb/ft * 3.08 * 2 = 2064 and it came with a 241. I've beat it pretty hard and the case has held up nicely.