If you're having trouble visualizing this, do this. Watch YouTube videos of jeeps wheeling, in different places. Then look if they included a spec list in the video, or comment section. Find one with a Dana 35 and tire setup close to what you want and watch how it wheels. Maybe that can help visually 🤷♂️
Should I upgrade my Dana 35 axle?
Once upon a time I would have told you no, don't waste your money. However, knowing what I know now, I wouldn't hesitate to build a Dana 35 axle. If you're planning on running 35" tires or larger, I wouldn't bother starting with a Dana 35. However, if you don't plan on going larger than 33" tires, a built Dana 35 should be more than up to the task. By replacing the axle shafts with chromoly ones (I recommend Revolution axle shafts), upgrading the ring and pinion, as well as the carrier and adding a locker, I think you'd end up with a really solid axle for 33" tires.
Blaine (who I consider to be one of the most knowledgable people in the TJ community) has pointed out to us that there is a guy out there running a built Dana 35 axle on 35" tires and has no issues at all breaking anything off road. Jerry Bransford has also pointed out on numerous occasions that a built Dana 35 is up to the task.
So there you have it, two of the more knowledgable guys in the TJ community who are not dismissing the Dana 35 as a decent axle to off-road with.
Make no mistake, a built Dana 35 is a strong and capable axle. Obviously not as strong as a build Dana 44 (or similar), but if you're not going to be running anything larger than 33" tires, a built Dana 35 should suit you just fine.
In the case of the Dana 35 and the parrots all over the internet who always like to repeat things like, "Don't build a Dana 35, you'd be polishing a turd!". Well, those people likely have ZERO experience with a built Dana 35, and therefore they don't know what one is capable of. They just heard someone say not to build a Dana 35 10 years ago, and have been repeating it ever since as if it has any merit whatsoever (it doesn't). That's how rumors get started, and this is one of those rumors that has no truth to it whatsoever.
Sure, a Dana 35 in stock form will be easily destroyed by a set of 35" tires and some off-roading. However, a build Dana 35 is another story altogether. Don't underestimate these axles!
Of course there can be no question that a Dana 44 will always add more resale value (and bragging rights) to your TJ, so there's always that to keep in mind!
Oh, and remember, no matter how strong of an axle you have (even if it's a built Dana 60), that can't stop it from being destroyed by a piss poor driver. No matter how indestructible you think your axle is, no axle is indestructible against bad driving skill.
4340 vs 1541H axle shafts (and why 4340 is not a good choice)
The following is a quote from @mrblaine in another thread regarding upgrading the Dana 35 axle shafts:
There's a whole bunch of confusion and one side of the equation going on so far. First, let's get apples to apples in perspective. 1541H is a case hardening alloy. 4340 is a through hardening alloy. They are not readily interchangeable due to the 35 axle having a bearing journal that the bearing rides on directly without adding a hardened race. For that application, the superior axle material is 1541H because it is plenty strong and because it is case hardening, you can bring the surface hardness up high enough to withstand bearing rollers riding on it. "IF" you try to bring 4340 up to the same hardness, it will be brittle because there is no ductility left at those levels of hardness. The 1541H will have a very high surface hardness with a softer core for a good level of ductility.
This is typical of what 4340 does when you try to use it for a bearing shaft and don't nail the heat treat.
The very same thing that makes 4340 difficult to use for bearing shafts is what makes it a great material for non bearing shafts like the Dana 44 with Set 10 bearings. Since the hardness for a bearing journal isn't an issue, the heat treat can be brought up high enough that there is a lot of ductility left and a fairly high level of hardness throughout without it being brittle.
1541H Dana 35 shafts don't scare me, 4340 Dana 35 shafts scare me a lot.
Nailed the difference in the surface hardening alloy. It might also be noted that the 4340 is fine for front D30s, but Dana 35 bearings ride directly on the shaft, and cause the axle to flex. It's this flexion that causes non-concentric torque, and causes brittle 4340 axles to fail. 1541H axles are much more flexible; and if properly surface hardened will retain the hard surface and also flexion.