I'd get the total spline 23 spline input shaft from Marlin for the rear box. And I'd put the 4.7 gears in the rear box and 2.28's in the crawler box. If you put the 4.7's in the crawler box then the multiplication torque is going into the input shaft of the rear box. Not really ideal when you can just put them at the last chain of output.
I'd probably also CSI your usage requirements ensuring you'll actually need 10.7 total low range..... dual 2.28's at 5.2 is pretty low! 2.28 and 4.7 at 10.7 is like....holy low and slow. Major rock crawling trails all day kind of low. Might save yourself the money and keep er dual 2.28's? Although I suppose having 10.7 at the t-case could make up for a high geared diff if that was the intention.
4x4wire review of the 4.7 gear set suggests there's more slop in the gears... A reason I wouldn't bother going with 4.7's for sh*ts n gigs.
Food for thought, anyhow.
This. I have dual 2.28 and have never needed more. IMHO, 2.28 + 4.7 is marketing hype and a conspiracy to separate you from your money. It's also something you can brag about to your buddies. I guess under extreme rock crawling it might be useful, but I just can image where 2.28 + 4.7 + 1st gear could be practical.
Sorry, I haven't updated this in a while since I have been focusing on
my build thread for the 4Runner.
There are a lot of moving parts to this dual case conversion, so I'll try to be as clear as possible.
I bought the Marlin rebuilt R151F transmission and Marlin rebuilt 2.28 transfer case from a buddy with zero miles. The Marlin t-case is forward shift and already has a 23-spline input shaft to mate to the R151F. And it also has the upgraded Marlin 30-spline heavy duty front and rear output shafts on the rear housing. Edit: I’m wrong. I went back and measured the output shaft diameter. The Marlin rebuilt t-case only has the heavy duty flanges, not the upgraded 30-spline output shafts.
If I want to run dual cases, I'm going to have to split the Marlin t-case either way. And the front half of the front case should be the Marlin 2.28 case (to run the forward shift portion of the case on the R151F). And the rear half of the second rear t-case should have the Marlin 30-spline output shafts.
That leaves us with the rear transfer case. I picked up a used top-shift t-case with zero history. I wanted to rebuild it anyway, because I didn't know the condition. So I just splurged for the Marlin 23-spline 4.7 gear set, since it's basically a complete rebuild kit anyway. And I bought the 23-spline Marlin dual case adapter, so I'm running 23 splines in both cases. I will probably get FROR twin-stick kit so I can run 2WD/4WD and Hi/Low separately.
It's true, the 10.7:1 t-case gearing is super-low. But I don't
have to use all that gearing. It just affords me a lot of options. Plus, I'm not obligated to use 1st gear in the R151F.
I suspect (but don't know for sure since I bought the R151F second-hand) that the transmission has the 3.83 1st gear option based on what the Seller told me.
So these are the final drive options I will have in 1st gear if I keep the 4.10:1 diff gears:
Front Case High, Rear Case High = 15.7:1 Final Drive
Front Case Low, Rear Case High = 35.8:1 Final Drive
Front Case High, Rear Case Low = 73.8:1 Final Drive
Front Case Low, Rear Case Low =
168.3:1 Final Drive
With the OM617 diesel, 33" tires, and 4.10 diff gears, I will have a wide variety of options - from keeping everything in high and getting great mileage on the highway, to fully low-low and being able to crawl over anything at diesel idle. Plus all the options in-between.
Overall, I'm pretty excited about how this is going to turn out. With a rear locker the 4Runner should be unstoppable. But I've got some other maintenance items to address first (brake master cylinder, rear axle seals, tires, etc).
Right now I'm just waiting on the dual case adapter to ship from Marlin, then I can start tearing into the dual case build.
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