Reliability of 4wd conversions

S2DM

Adventurer
I'm in the early design stages of a new camper build, basically deep into solidworks renderings, and once again, facing the great debate on which base vehicle. We'd really like to be smaller than our current f550 is, but we also need more room for kids and dogs. Hence, I've been considering a 4wd conversion on an Isuzu NPR crew cab. There are a few of them running around and a few guys have more than a few under their belts or currently being built.

Keeping cost considerations aside, how reliable would the crowd estimate a well done 4wd conversion, with new dana axles front and rear, a very good quality transfer case and put together by a skilled builder (not myself)?

I know the quigleys, UJOR and sportsmobile conversion have a long track life at this point. Given the NPR is offered overseas as a 4wd NPS, which is largely the same, it seems once you get through the fitment issues, a well done NPR conversion should be robust as the truck was originally engineered to be able to accommodate a 4wd drivetrain. But, I'm also out of my element here a bit so any advice appreciated.

It would have a Dana 80 front, Dynatrac pro rock 80 rear and either an NP205 or Trail Worthy hero transfer case.

What I keep on coming up against design constraint wise is what I faced with my first build, the extra length of the super duty platform in a crew cab makes for a pretty long vehicle. We are really looking to get more nimble, are ok with sacrificing a little long freeway run comfort for in town and forest road maneuverability comfort, and had kinda already anticipated being 100k in on the base vehicle either way. Obviously its preference, and some will (again) think I'm crazy, but I'd really like to do a crew cab thats closer to 21' total length and substantially narrower than the 93.5" to outside of tire my current rig is. We just seem to always end up in situations where the smaller size would be desirable and I'd like to use the rig more for day trips with the fam as well.

My concern is I'd like something relatively trouble free and easily serviceable and I don't know enough about these conversions to know whether once the initial hiccups are smoothed out, are they just as reliable as say, a stock super duty might be?
 

Wilbah

Adventurer
What about some factory 4x4 versions in cab over like FUSO or some of the medium duty trucks- international, even peterbilt and kw I think offer medium duty cabovers but I may be wrong. I also dont know specifically which ones offer 4x4 either, but I'm thinking then you get something with a warranty to rely on rather than an upfit version that may prove problematic. Another option might be a used Mog or its variants, lots of those and while they might require work to fit exactly what you want, buying used may save you some $, and they do last a long time (albeit with maintenance). I am not sure where you're located but theres a guy in SE CO that deals with Mogs alot. Might be worth a call to discuss various options to get his perspective. I can track down his name if it helps.
 

S2DM

Adventurer
I should have clarified, Fuso really not an option. I don't want another older truck and the new ones are too problematic IMHO. I've had a Mog and that falls under the "never again" category (I actually just got the chills :)

Suffice it to say Ive done a ton of reading and for COE in the size range I'd like, I don't see another option other than an NPR conversion (If we go the COE route).
What about some factory 4x4 versions in cab over like FUSO or some of the medium duty trucks- international, even peterbilt and kw I think offer medium duty cabovers but I may be wrong. I also dont know specifically which ones offer 4x4 either, but I'm thinking then you get something with a warranty to rely on rather than an upfit version that may prove problematic. Another option might be a used Mog or its variants, lots of those and while they might require work to fit exactly what you want, buying used may save you some $, and they do last a long time (albeit with maintenance). I am not sure where you're located but theres a guy in SE CO that deals with Mogs alot. Might be worth a call to discuss various options to get his perspective. I can track down his name if it helps.
 
My worthless suggestions:
If there’s a factory diesel delete EGR and any other post 2006 emission items. Keep factory 5 or 6 speed manual. Add very HD gear drive transfer case. Keep factory rear axle, add Detroit Locker. Use Dana 80 as front axle as minimum. With ARB.
Avoid sexy 18” tires, use either 325/85R16 Michelin XZL if 16s will fit and 5000kg/axle is enough, otherwise use 335 or 365/80R20 XZL or other mfgs equivalents. Adjust diff ratio accordingly. Make sure front is same as rear or up to 1% faster but not slower.
Do not use air suspension. Do not replace diesel with Chevy V8.
If vehicle is heavier than Isuzu NPR forget about Dana 80, use much heavier front axle with locker. And heavier tires.
 
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pappawheely

Autonomous4X4
The truck doesn't know whats under it. You can mount anything you want as long as you have a competent fabricator designing and installing the mounts. I have owned several vehicles with entirely revised suspensions that had zero issues. You just need to watch the same parameters that the factory engineers do. It sounds like you are needing a divorced transfer case? I was chasing down a divorced 205 for my build, but could not find one so I bought a dana 24. Before it was even delivered, a friend found a 205 for me. I'll sell you the dana 24, or If you want a divorced 205 I can have my contacts look for you.
 
Whatever you do, make sure what is used for parts is well documented and understood. Your going to have to be the smart one at oreillys guiding the part guy to what you need.
 

nickw

Adventurer
I'd disagree with some folks above saying bolt up good parts and you have a good rig. I'd say that an OEM vehicle is an engineered "system", not a bunch of heavy duty parts bolted together. For instance, do you want a front axle shaft that has a torque rating above that of the Tcase or Trans? I'd say no, front axle shaft is a much better fuse than a Tcase for obvious reasons. Drive shafts fall into this category too along with things like tie rods, etc. Any differences in frame construction between 4wd and 2wd?

Some of the more well though out conversions have a history of performing well like the sportsmobile, obviously yours wouldn't fall into this category, regardless of how well it was constructed.

Also the lack of being able to drop the thing off someplace for repair is something to consider, it's obviously not going to the dealership. No warranty concerns?
 

javajoe79

Fabricator
I am building an NPR 4wd conversion. See my build thread. The NPR is designed to handle a bunch of weight so it makes for a good platform frame wise. Your typical camper on an NPR with 4wd won't end up that heavy. From what I have seen, similar vehicles often weight around 12-14k when finished. That is well within the weight limits of typical axle that you might use. I bought my truck as an unfinished project. It already had the stock rear end removed and replaced with a sterling 10.5 and a Dana 60 up front. I'll be running the 60 for now as I don't plan on this camper being extremely heavy but I am on the lookout for a front axle upgrade.
None of this is really revolutionary in that people have been building tough and reliable trucks with these components for a long time. As long as you do your homework, utilize good fabricators when needed and use parts that can handle the weight, you should be fine. In my opinion the NPR and similar trucks are overbuilt on purpose to prepare for the inevitable abuse and overloading that a fleet vehicle might see in the hands of someone who doesn't care about the truck because they don't own it.
 
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