Will a 21 spline toyota case hold up in this rig?

paulevans76

paulevans76

Well-Known Member
Joined
Mar 21, 2005
Location
York, SC
I've got an old SAS'd Isuzu trooper, tipping the scales around 4k+ lb, and it will soon have a fairly peppy 3.4 GM v6 under the hood to replace the tired 2.8. It will likely never make more than 200hp and 225ft lb, it will probably be more like 175/200 ish. The axles are geared at 5.38, and I'll be running 37's for a while, and potentially a 38-40 in the future.

I've got a few drivetrain options I'm kicking around (literally, my garage is littered with stuff), one of which is a 2wd sm465 to a single divorce mounted 21 spline toyota case. I found one of the old OTT divorce mount adapters (21 spline) and got a top shift case for cheap. I would likely regear it to 4.7 and maybe shell out for whatever HD output(s) is/are available. 1st gear hi would be a great trail gear, and with the case in low I'd have a large range of crawling speeds. It would suck on the road quite a bit with the sans-overdrive 1960's garbage truck trans though.

I feel like while the deeper axle gears mitigate some of the strain, I'd still be running close to double the power of a 22r in front of it, and if I ran the sm465 it would be like crawl box torque when it's in the 6.6:1 1st gear. Plus it's not exactly a lightweight rig.

I'm mostly running the standard NC, SC, TN trails, some moderate and hard-enough-to-break-shit stuff, but nothing too extreme, and usually only once a month or two. I drive it to and from the trails (and the mall).

So do y'all think the 21 spline case would hold up, or should I explore other options? I like to have some margin of 'stupidability' strength, so I don't want to have to go easy on it all the time.
 
I would like to say no it wont, but I have been running 21 spline duals (2.28/4.70) in my tacoma since January and to my surprise it hasn't grenaded yet. I wheel with some sense most of the time but I lay into from time to time. I've got a 3rz with 5.29's, 39.5's, and weighed 3980 lbs before I swapped the fj80 rear axle in.
 
You would be pushing it for sure people do it all the time but I have broken several with 22r on 37 or 38 inch tires
 
It seems like the same sorta non-consensus most of the places I look. On pirate there's a lot of dudes out west running sticky dry rock binding up everything, and I can see that taking parts out easily and give the impression that there's no way to make it really last. Out here there's usually less traction but more wheel speed and potential shock load.

So karatejosh were you running the rcv or marlins upgraded output? It's crazy to think people are grenading a case before popping a driveshaft ujoint or something.
 
paulevans76 said:
It's crazy to think people are grenading a case before popping a driveshaft ujoint or something.
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Depends on which is weaker under that amount of torsional load. If the case was never origninally designed for that amount of torsional load or engine power, bad things happen. Loads get high, the case gets twisted, shafts misalign and gears don't mesh properly under load all of a sudden, and things break.
 
I exploded a rear stock output I have a rcv now I in have broken 2 I'mput shafts in my last truck and jonathen striped the gears in his 23 spline duel cases all where being a 22r with 37 or 38 inch tires a toyota ujoint is dam near impossible to break unless worn out
 
Yeah that's true they are a great tough u-joint. Well, I was hoping I'd be able to make this thing work, and it probably would for a while, but having the transfer case as the fuse just doesn't seem like the best idea. And building it out with all the best stuff would put me close to atlas price. Back to the drawing board.
 
Yeah I'm in that boat now; I don't see mine lasting forever. I might just wait till it grenades and see if TG will warranty it with a 23 spline gearset and a new coupler. I have seen them do that for someone recently
 
Hey Paul, I was in similar situation a year or so ago when Chris and I sat down and wrote out every option as if money was no option.
Then we backed down to strength and sustainability. One option was to tear the trans apart and adapt a Yota output to crawl boxes - which has indeed been done by a few people we know on the Planet and some other guys years back from 4x4wire.

Anyhow, chose to swap to the Ar5 trans which in the end I lucked out with the 27 spline rear output and finally gearing the case down a few weeks back.

At this point you're limited by your front output length but also in your current motor's horsepower, so that's the reason why you want to go 3.4 V6, right?
Well you'll end up about same HP as the 3.2 V6 I have roughly 200ish. If you go with the Yota cases behind the sm465, I say gear the case down and see if you can get a hold of a 23 spline output and make it happen. I think that is the most beef you can get for the Yota output. Someone correct me if I am wrong.

IIRC, you're going to run only one case and not a dual setup? If you run two, perhaps only gear down one of them.
Let your hubs be the fuse and joints if something happens.
And I think you nailed it best when you compared dry sticky out west to spinning 'shock' breaking shit out here. Torsional load is still something to think about but I think you got it covered with those RCVs once you get them in.
 
Lorenzo816 said:
Hey Paul, I was in similar situation a year or so ago when Chris and I sat down and wrote out every option as if money was no option.
Then we backed down to strength and sustainability. One option was to tear the trans apart and adapt a Yota output to crawl boxes - which has indeed been done by a few people we know on the Planet and some other guys years back from 4x4wire.
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I considered this, and looked into it, but ultimately the ~175-200hp and ~200+ft lb would be too much for a G series (easiest swap) pretty rough on a w56 (somewhat difficult swap), but ok for an R series, but we are talking a bit of a potential mess of a swap and then again we move the fuse to the case.

Lorenzo816 said:
At this point you're limited by your front output length but also in your current motor's horsepower, so that's the reason why you want to go 3.4 V6, right?
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Yep. Front shaft is 22" and I'm limited on uptravel until I chop into the frame more, so with droop being all I potentially have going for me, it's limited by driveshaft joint bind, which I've also minimized with an oliver's shaft with single toyota joints, although it was initially setup for a cv shaft (pinion pointed at case). I get vibes at speed, but on the trail I get as much angle out of the shaft possible.

The hopped up 3.4 pops right into place of the tired 2.8 and i can use all my intake, exhaust, accessories, computer, etc.

Lorenzo816 said:
Well you'll end up about same HP as the 3.2 V6 I have roughly 200ish. If you go with the Yota cases behind the sm465, I say gear the case down and see if you can get a hold of a 23 spline output and make it happen. I think that is the most beef you can get for the Yota output. Someone correct me if I am wrong.
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It was actually going to be a 2wd sm465 to a divorced yota case. Married trans and case wouldn't net me any driveshaft lenght up front. But divorced, with a short but adequate (ba dum ching!) intermediate shaft between the two, I'd end up with roughly equal length front and rear driveshafts at around 3' each, more than plenty to get a shit ton of droop out of the suspension. The divorced adapter I have is a 21 spline unit and they aren't made at all anymore, so I'd be stuck with a 21 spline input gear set if I use it.

The other part I really ignored is that the 3.4 probably really isn't going to have the balls to run the sm465 on the road. 2nd, 3rd, and 4th are all pretty far apart from each other, and it's more streetable with a torquey v8. Plus no overdrive.

Lorenzo816 said:
IIRC, you're going to run only one case and not a dual setup? If you run two, perhaps only gear down one of them.
Let your hubs be the fuse and joints if something happens.
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Just one tcase, since with the sm465, I'd have the 6.55:1 first gear, plenty of reduction. But it's sorta like having a crawl box as far as torque input into the case. On paper, 1st gear high range would be a great general trail gear, and 2nd-4th in low range with 4.7's in the case would give me plenty of options, and 1st gear low would be mega low for super technical/hairy situations.

Lorenzo816 said:
And I think you nailed it best when you compared dry sticky out west to spinning 'shock' breaking shit out here. Torsional load is still something to think about but I think you got it covered with those RCVs once you get them in.
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Yeah I'm not worried about the axle anymore, but I'd be worried about blowing out the case or spending a shitload of money to bling one out and still potentially break it.
 
I think I'll hold on to this stuff for now, but a tougher, simpler setup probably exists, I just have to narrow it down.

I do have a 60* 700r4 I could use, but I'd have to rebuild it, swap on a 4wd output and either run a dana 300 (more expensive, some potential driveshaft/trans pan interference issues) or an np241c (cheap, easy, tough), or get an expensive AA adapter to a 23 spline yota case and buy 23 spline gears and the rcv output, blah blah, too much money. But rebuilding would be expensive and then although the 700 has an overdrive, it's .7:1 where my current OD is .81:1. This thing would end up running in 3rd most of the time on the road and bigger tires would make it even worse.
 
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