Great info to have, thanks for sharing this.

Questions:
Can you share your 34" tire info/specs?
Also, can you share trail ratings and conditions you were on before the mech. failures? Rocks, mud, sand, 5+ rated trail, etc.

I think it's very hard to get a really good answer of where the limits are because of so many variables.

It varies so much by how the driver uses the vehicle. For example when you start to bounce on a rock ledge, do you back off or pedal down? How many bounces do you let it go before easing off. Does the driver try to force the tires to turn when bound up or back off when they feel the steering rack max out? that probably makes the difference between blown rack or not in a lot of cases.

Experienced drivers tend to make vehicles last a lot longer. I've broken multiple steering arms and boxes in my trail rigs. It's just something you learn from breaking things how far you can go.

The weight is a huge factor that varies a lot. I see so many 4Runners loaded with weight and are at a lot more risk than a stock weight vehicle. Weight kills performance and parts.

Tires matter a lot too. Sticky tires at low pressure have a lot more traction than hard rubber tires at street pressure.

And terrain is also a big factor. Shock loads tend to be the worst for drive train parts. So spinning in mud for example is a really good way to blow up a diff or axle. I rarely see broken junk in Moab on slickrock outside of bouncing causing shock loads. Traction is really high, but rarely is there a spinning tires and then instant traction. And using momentum on slickrock is almost never the right choice. But on a big muddy rocky hill in the east - you might need to use momentum and spinning tires to get up that risks more shock loads.

Anyway, just sort of a comment that there's probably not a one-size-fits-all solution. It seems like 33-35" tires are pretty functional. 37's are maybe too much for the front end. Rear axles seem to be able to handle almost any tire size you can fit, which honestly is remarkable given the weight of the 4R and size of the axle. Going beyond 35s - I'd be swapping vehicles for a Land Cruiser. When you run through the list of upgrades needed for durability, it's cheaper to just swap for a land cruiser.

Is this poll based on stock gear ratios?? Running 33's, I want bigger but regearing looks $$$$$. No problems on 33's with diff drop. Anyone jack there stock drivetrain up on bigger than 33's??

Vehicle: heavily armored, regeared, twin locked, and completely gusset/armored mid travel setup.

Yokohama geolander 285/75/17, measures 34.1, 63lbs. I think these and km3's are your lightest 34 MT's. I went with the Yoko's over KM3 because i wanted a true 34..

Desert Mobbing (anzo/mohave road): blown king shock, wore out suspension bushing, starting to bend alignment tabs, wore out steering rack, bent spindle on 33.s

rock obstacle (valley of moon): blown tie rod/CV on 35's.

Hill climb/ mixed atv/cow trail (bodie hills/mammoth, ca): blown shock on a rock, bent rear lower link, high trans temp, destroyed alignment tabs, and Destroyed lower A arm bushings on 33's.

Sand/dune (boxcar canyon, NV): no damage on 33.

Mud (private property): no damage.

Moab, Utah (fins and things): no damage on 33

Canyonlands, Utah: mix trails: no damage on 33

Victoria Mtn, NM: No damage, mix trails on 33's..

Easy way of thinking: While, i broke and bent alot of things on 33's, I didn't have to carry spares to make it home.

Compared to my 200 LC, the 4Runner has an inherent drivetrain safety feature called: 'lack of power'

I found that front CV's in high power / snappy torque vehicles with upsized tires seem to be less forgiving with too much skinny pedal.

oh yea, cam tabs are trashed on mine as well. also inner wheel wells from full bump.

Thank you for all great details in your post. I think this is my preliminary assumption about these rigs that, though many other factors need to be taken into account, 33's are very sustainable for most terrains and applications.

34's are bit tougher on the drivetrain, but also survivable.

35's will likely pop a CV if you get into it, but the front diff, transmission, tcase and rear diff are all good to go. Even in popping a CV - it's a fairly straightforward repair that only requires familiarity, safe jacking and a few key tools, other than a normal tool kit.

The 5th gen is a massive improvement in the design of the front spindle upright and lower ball joint assembly for field replacement of the CV. It's a super easy job because of how that lower spindle area separates with 2 bolts for the ball joint bracket. It's an easy trail side repair. The older setups like the LC100 were a huge PITA to do.

X2. All i needed to add to my kit is a 35-36mm socket for the axle end nut. (Not the castle nut, but the inner one)

Depending on how crazy you want to go on being prepared - you might also include a wiper seal for the diff housing side. Sometimes those get chewed up when you blow an axle if it flops too much. I toss them in for remote trips just because I happen to have them around, but you can get off the trail even if the seal is shot without replacing it. You'd just have to fix a second time after you get home in most cases. I have had the seal fail on its own though - probably due to the needle bearing issue. It was on that side, but preceded the needle bearing going out by about 10k miles. I assume they were related. I bought the ECGS bushing, but toyota warrantied it and it hasn't returned. So I keep a seal and the ECGS bushing ready to go if it happens again.

I also like to have a wood chisel for removing the dust cap on the hub. You won't deform it with a fine cutting edge like a wood chisel that you can tap under the lip and pry it off. My other suggestion is a medium length drift or steel chisel, or even a piece of pipe. Something you can use to remove the inner CV from the diff housing. If you haven't done it before - the inner CV has landings machined into it that are there for you to put a drift against and hammer them out. No need for a slide hammer or using a pry bar. Just put your rod/drift/pipe/whaver against the landing and whack with a hammer and it'll pop that snap ring out without any drama.

If i were to add any other spare parts - I'd carry a spare rear drive shaft. It's exposed and mine has a fair bit of trail rash on it. There's not really a good way to protect it and they're around $100 or less for a spare. I don't think it's necessary, but if I were regularly going to the harder places like Johnson Valley or the Rubicon, I'd have one along. For normal exploring it'd be totally overkill.

Wheels bearings too from what it looks like?

I did actually have one small issue this post reminded me of. On 33's. After a good rough trail day I noticed fluid dripping from my right axle (OEMs). Got under to see it coming from the differential dust seal. Those seals are tough as heck! It wasn't damaged but got knocked slightly cock-eyed out of flush. Luckily not inwards towards the diff. Just removed the axle which is super easy now on the 5th. Knocked it back to it's proper position carefully. Too far you're breaking it out and buying a new seal. Back to new 😁

I think you still need a press to swap over the hub parts. But I've never done it on either one. Swapping an assembled hub/bearing combo would be quick and easy though. I think it's just 4 bolts and a wire connector beyond removing the CV.

I think the rear wheel bearings are a PITA on both like they always have been. Not something you'd do trailside. Haven't done a rear wheel bearing on a 5th gen either. Visually they look just like the prior generations.

From what I seen you can simply bolt on a new hub with bearings already in. It looked doable as a trail repair with a deadblow hammer and finangling around the rotor shield. I dont know about LC100 but on the older 3rd gen you have to take the whole knuckle arm off and use a shop press and even then it's a still PITA. It's all pressed together. The 5th gen looks a lot simpler and beefier in general. Like the LBJ bolts you mention, the 4 small ones on 3rd gen have been known to shear and that whole upside down LBJ design wheel falling off thing.

My intact dust caps will attest to the wood chisel technique. What do you see happening to the rear drive shaft, it gets damaged to the point the slip joint cant work or what?

Never had any luck with the CV drift method (the FSM way) I always had to resort to a prybar on those lips, which sometimes still doesn't work so I resort to careful prying against diff housing. Even with the snap ring hole in correct orientation and a bit of grease holding it. Maybe I'm doing something wrong I dunno.

Another tip I can think off is I noticed Autozone sells valvoline gear oil in squeezy bags. Takes up less space and you don't need a pump (which inevitably breaks half way through).