np231 doublers

[pointsnorth]

so not a jeep guy by any means so bear with me on this. been working on np231 for a customer. and have ended up with numerous spare parts kicking around

I know that the ax5 five and ax15 are made by aisin with has supplied toyota with transmissions forever. now its a bolt in swap to put toyota duals behind either of these trans after swapping out the ouput shaft for the toyota shaft.

so here is my question is it then worth it to go the other way and swap a 231/d300 setup into a tacoma or is the 231 like the rest of the jeep

[Scott Cee AKA 2drx4]

They work fine. They'd outlast the D300 you bolt to it. Honestly the worst part of them is if they're the DIY type, that uses a welded up stock front case half, it's a lot of weight to hang off them, although the D300 isn't as heavy as some other options and probably wouldn't be an issue. If you do the NWF Eco-box you'll never have an issue, although they do recommend using the 6 planet style of planetaries found in the 231HD or 241 and bigger tcases, but that recommendation is really only applicable to higher input power levels than you're likely to see.

[pointsnorth]

you say it will outlast the d300. Ive noticed guys that are actually building jeeps have a dislike for the d300 why is that?

[Scoobienorth]

I’d think the big reasons jeep guys tend to not like the d300 is that it drops the wrong side, flipping it they leak, and getting harder to come by. With the added torque from a doubler can push the d300 to much and blow up. Steve my buddy with the flatty sold a d300 to Ivar the owner of Kelowna transmission last year after his yj destroyed a d300 with a 231 eco black box setup. He now keeps a spare d300. He’s running 44/9” with 40’s and a 4.2 motor.

[pointsnorth]

So my next question in that senario is the d300 weakness caused by not having enough gearing in the axles and then adding a doubler on the upstream side your making the 300 the breaking point? say 4.11 thats a great highway gear but increase the strain on the 300 when wheeling. and at the opposite side is 5.38s that dont make a great highway gear but will take some of the strain off the 300

[Scoobienorth]

In the case of Ivar I can’t remember the specifics but knowing he is one of the top transmission and diff guys in the okanagan, and a well respected experienced wheeler I’d think his diffs are geared on the lower side. It’s a really nice build.

[Scoobienorth]

The setup is pretty stout especially within reason. I wouldn’t scrap the idea on the fact that a 30+ year old tcase failed. Big power or a full throttle bouncing style I’d probably move on.

[Scott Cee AKA 2drx4]

The D300 in stock form isn't much stronger than a stock NP231. Pretty easy to break outputs on them. Which then leads to the cascade of upgrades until you've dumped as much money into them as an Atlas. Great tcase for a small/light rig with lower power levels, but absolutely not great for anything over 5000lbs (pretty easy to get there with a full body), or a doubler and a heavy foot will definitely exploit the weaknesses.

For the slight weight penalty difference, the NP205 runs circles around it, which to me is the final nail in the coffin. But I'm not really light, and don't intend to build anything light, since it's just a losing battle if you want something you can street and do longer trail rides with.