The 201 is a twin-stick design, with an interlock to prevent engagement in 2-wheel low. The FM says that this is to protect the internals and driveline components from the 2X torque low range can deliver, yet there is a caveat when this consideration is subjected to the "smell test." Obviously, the input shaft torque to the t-case can be no more than what the conisderably smaller input shaft to the transmission can deliver. Moreover, the torque going into the t-case is the same in 2-wheel low as it is in 4-wheel low. So none of that is different. The only difference in terms of protecting the driveline is on the output side of the t-case going to the rear axle which is after the output gear that doubles the torque.
This is where the real issue lies.
The biggest difference between the two boxes is the splines on the gozintas and gozoutas. The 1-3/8 10-spline shaft on the 201 is considerably weaker than the 32 spline 205. 1410 series yokes are available for both. Learning that, I stuck with the big factory yoke on only the rear (10-spline) Dana 60 so that the U-joint would fail there before anything else in the driveline system did. Effectively, it's a shear pin.
Having done a considerable amount of sleuthing among IH fans, I've learned that there is a much more significant difference between the two boxes.
In the interest of reducing instantaneous loads on the driveline, engineers at New Process developed a two-piece gear for the 201 with springs installed on lugs between the gear and the 10-spline shaft. One of these IH posters, who drives a heavily-loaded Travelall, rebuilt a couple of these boxes after which the springs were subject to early failure. Mr. Bruce Frank posted photos of the respective gears here: (https://www.steelsoldiers.com/threads/m ... 031/page-2 (yes, I know the thread is about an M37)). He went so far as to weld the gear to the shaft, after which he subjected it to 200,000 miles with no problems.The 201 had no problems with lubrication. What they did have is a primary output gear that was a two piece unit with cushioning springs between the interface of the inner and outer part of the gear. That was a mistake, but NP continued to produce and sell that T-case to both IHC and Dodge for about 10 years.
The gear chews up the springs and the engaging teeth between the parts of the gear slap back and fourth during stops, starts, and cruise above 40 mph. Even if no repairs are made the gear takes the punishment for hundreds of thousands of miles.
BTW, that gear repaired starts slapping back and fourth in about two months. Only way to correctly repair is to weld the inner to outer part. Some care with preheat and post heat makes for an absolutely bullet proof repair. I put 200,000 miles on my welded gear with not a problem.
In the NP205, New Process eliminated this two-piece gear design on 32-spline shafts, a design they stuck with for 20 years thereafter. On the other hand, the NP205 has an internal interlock to prevent going into 2-wheel low. What I used to do in the '69 W200 in order to travel on asphalt along our property at very low speeds with (volumetrically) huge poorly secured loads of tree tops and brush was put it in 4-wheel low and unlock the front hubs. I did blow out the factory 1301 series rear u-joint doing that, but it was old and pretty roasted. I do this often enough that it's a PITA. In building a new truck I don't want PITAs.
Now, here comes the kicker: My NP201 has this beefy Braden PTO on it with 1.25" shafts both fore and aft. I need that to run the winch on the front and the hydraulic pump for the dump bed. Being an NP201, it's an 8-bolt PTO I can't put on the 6-bolt 205 PTO interface. So in order to use my NP205 with its indestructible internals as intended, I'd need 1410 yokes, a twin stick setup (they're available), and a PTO with dual output shafts (1" minimum). That's at least a grand of cash. I've already bought 1410 series U-bolt yokes for the NP201, a sunk cost of $300 and a gasket set for painting.
So this whole question revolves around that two-piece output gear. What is your experience with the NP201? Terry says he's never seen the two-piece gear. I've looked around various fora online and have seen discussion about the problem as described. If I go into my NP201 to replace gaskets, I'll probably take a look. There may be an option to welding it, assuming they're coils, I could simply install steel shaft stock, but that would put those high instantaneousl loads into that weaker 10-spline shaft.
If time and money were not objective considerations, the obvious thing to do would be to go with the NP205 and blow the dough on the new PTO, linkage, yokes, and toss in a different rear axle so that the entire rear driveline would be 32-spline shafts. Barring that (at least) three grand, and having already rebuilt what I have, I'm not thrilled with that option unless I was going to a DRW axle, rear disc brakes, springs, etc. OK, so call it five grand and at least a month's work and delay.
Sigh.
