23 spline rear case question?

[nismo5]

hey guys im gettin ready to order stuff to run duals and i wanna run 21 spline front with stock 2.28 gears but in the rear case i would like to run 23 spline and 4.7's but what i dont understand is at what point do i convert it over to 23 spline ?? im sure i need 23 spline 4.7's but do i need a 23 spline dual adapter ?? will a 23 spline adapter work on the back of my 21 spline front case ??

thanks guys 

[bryanrz]

I also have wondered this, where the switch happens, I'm sure someone will chime in quick

[toe]

There's a 21 or 23 spline coupler that goes in the crawler box that connects to the transfer case.

[nismo5]

so if i order a 23 spline dual adapter it will still bolt up to the back of the 21 spline front case ??

[toe]

I'd talk to them to make sure everything is ordered correctly..............

[Jdlucasjr]

I'm pretty sure you can order a 23spline output for the crawl box..

[BigMike]

but what i dont understand is at what point do i convert it over to 23 spline

I also have wondered this, where the switch happens

Interesting... I've never thought to add this info to our website -- I will come up with something and add some useful info soon!

Here is a basic Marlin Crawler dual case drive train run-down:

Engine > Transmission > Transmission Output Coupler > Crawl Box Input > Crawl Box > Dual Case Coupler (aka Crawl Box Output) > Transfer Case Input > Transfer Case

The Crawl Box Input spline is determined by the transmission output coupler. The rest of the setup is determined by the installer: You can use 21- or 23-spline components anywhere downstream of the Crawl Box.

Here is the typical 1979-1995 4-cylinder Marlin Crawler dual case run-down (non-Turbo) including spline counts:

20R or 22R or 22R-E > Transmission > 21sp output coupler > 21sp Crawl Box Input > Crawl Box > 21sp Dual Case Coupler > 21sp T/Case Input > T/Case

If you wish to run a 23-spline transfer case in this 4-cyl setup, then it would look like this (I did this on my truck):

20R or 22R or 22R-E > Transmission > 21sp output coupler > 21sp Crawl Box Input > Crawl Box > 23sp Dual Case Coupler > 23sp T/Case Input > T/Case

Note how the 21-spline Crawl Box Input must be used because the transmission has a 21-spline output. But keep these two points in mind: 1) The torque is multiplied by the Crawl Box, so its more advantageous to place the stronger 23-spline input downstream or behind the Crawl Box -- In other words it's where you want it to be anyhow as nismo5 is requesting, and 2) from the factory Toyota designed it for 21-spline here so it is reliable enough.

Case in point, when you hear of someone breaking an input in a dual case setup, 99.999999% of the time its the input in the transfer case, not the input of the Crawl Box. In fact I'd boldly wager that none have ever broke a 21-spline Crawl Box input, short of the input failing unnaturally (such as ran low on oil, or rust from moisture causing a coupler strip out) or it was used improperly such as someone installing a 4.3-liter Chevy V6 with a 21-spline transmission, a HUGE no-no .

It is a little different when you talk about chain drive applications which require our Transmission-to-Transfer Case Adapters:

This is because chain drive applications have the first coupler attached to the transfer case instead of the transmission, like this:

Engine > Transmission > Chain Drive T/Case Coupler > Chain Drive T/Case

In this case, which applies to the G58-equipped 4-cylinder (used in some 2nd gen 4Runners), the big block 4-cylinder (2.7-liter 3RZ-FE found in 1994-2004 T100s, Tacomas, and 4Runners), and all 1988 and newer 6-cylinders, we have to supply an additional coupler which is shown at top center of the above image. The dual case setup here looks like this:

Engine > Transmission > Marlin Crawler Trans-to-T/Case Coupler > Crawl Box Input > Crawl Box > Dual Case Coupler > T/Case Input > T/Case

It's a bit different but the concept is the same. So, if a 6-cylinder Tacoma owner wanted to have a sure-to-fail 21-spline setup, it would look like this (don't do this):

Engine > Transmission > Marlin Crawler Trans-to-T/Case Coupler (which is only available as 23sp) > 23sp Crawl Box Input > Crawl Box > 21sp Dual Case Coupler > 21sp T/Case Input > T/Case

This is like the opposite of what nismo5 is requesting. It's possible, of course, as all you need to do is use a 21-spline dual case setup and a 21-spline transfer case. But consider the additional torque from the engine and the increased weight of the vehicle and you'll end up with a broken 21-spline transfer case input and possibly also a stripped out and damaged 21sp dual case coupler.

To summarize:
Therefore, the spline count of the dual case adapter and its matching transfer case is entirely up to the installer. For instance, I am running a 21-spline transmission and a matching 21-spline Crawl Box but I immediately upgraded to the larger diameter and stronger 23-spline input at my transfer case by using a 23-spline Marlin Crawler dual case adapter kit.

You might be thinking why doesn't everyone with 4-cylinders just do this, and the answer is simple: It's an unnecessary added cost. The 23-spline input was only used for two years and on the least popular option - the 1986 & 1987 Turbo 4-cylinder - so its by far more difficult to find and wrecking yards charge more for it ... or you'd have to purchase an aftermarket 23-spline "Turbo Input" gear and hence the added cost. Moreover, 4-cylinder applications in my opinion do not need a 23-spline drive train. With our Total-Spline technology and Chromoly material, our 21-spline inputs are more then up to the task even when used behind the big block 3RZ. The reason to upgrade to 23-spline as mismo5 is looking to do is for insurance: If the upgrade is available and its much stronger, why not just do it?

We could even make a 21-spline Lefty transfer case and put it in a dual cased 5.7-liter iFORCE V8 Tundra towing a houseboat up I-80 if the customer wanted. We wouldn't warranty it of course

Regards,
BigMike

[bryanrz]

Thank you clears so much up!

[nismo5]

sweet!! thanks bigmike!!!  thats exactly what i wanted to know

[TimberlineBryce]

Circle the bases again Mike! Good info!! ...so in my case(punn intended) on my 3.0 2nd gen 4runner, if I go dual cases this is why I would need an extra 23 spline input gear? Then my setup would be 23 trans output/23coupler/23input/23dual adapter/23tcse input 4.7?

[BigMike]

Then my setup would be 23 trans output/23coupler/23input/23dual adapter/23tcse input 4.7?

This is correct Sir! You could use a 21-spline dual case coupler with a 21-spline 4.70:1 t/case input, but I strongly discourage this with your more powerful V6 and heavier 4Runner platform. Get a 23-spline dual case kit and use a 23-spline transfer case. It's the only way to go in my opinion.

BigMike

[locked 4x4]

I believe this makes sense to me but pictures are worth a thousand words.  Is there any way we could get some pictures to illustrate this?

[BigMike]

I don't have any proper images for this, but here are a couple that come to mind from my first build thread, reply #807:

modified 4-speed total-spline 21-spline input > 23-spline coupler > 23-spline Turbo MC Total Spline 2.28:1 input > 23-spline coupler > 23-spline MC Total Spline 4.70:1 Input.

So this is the most bullet proof setup possible with a 21-spline transmission output. Also both adapters are billet, MC08 and then the new MC08-R10

This is what we call a "Triple Case" which is comprised of two dual case adapters with a total of Three low range reduction gear sets. So there are two dual case couplers here and each coupler is contained in the shiny billet aluminum MC08-type adapters.

Not sure if this helps but maybe it does just a bit

BigMike

[RickerRicker19]

Just out of curiosity.....is your front driveshaft at more of an angle or your rear driveshaft with triple boxes? Each box is about 6" or so....that makes 12" added on to the tranny and t-case. You could almost swap your driveshafts or they would be very close to the same length. Also....how do you run the shifters for that?

[BigMike]

Hello RickerRicker19,

Good observations. You are correct, my front drive line does hang down more due to its extended length. I am running a FJ80 High Pinion front differential which helps but ideally I should use a carrier joint. It's never bothered me and I've never had a front drive line clearance issue before. I am running a heavy duty 0.190-inch thick front drive line from High Angle Drive Line for added insurance.

As for the drive line lengths on my short bed wheelbase, my front drive line is about 2-inches longer than my rear. So yes, they are interchangeable and I use this safety net instead of carrying around a spare drive line

As for the shifters it is nothing fancy. Just two Crawl Box levers and my MC Twin Stick levers atop my t/case. I have bench seats so there is more than enough room in there.

For reference, here is maybe the only interior photo I have from my build 3 threads:


What my drive train looks like being installed:


And here I do see some scratches on my front drive line but they are just minor, I've never "candy-caned" my drive lines before. Using a carrier bearing would have prevented this. I have no plans to change the setup I've got


(These images were lifted from my Return of the Project's page 4.)

BigMike