Marlin’s Dual Transfercase Adaptor
	Category:	Drivetrain
	Author:	toy4fun
	Date:	April 28th, 2005

With the addition of significantly bigger tires, gearing changes almost always come into play, especially when your 3700 lb. vehicle sports a 4cyl. After changing my ring and pinion to 5.29 and running 35” tires I still felt the need to go slower through the nasty stuff. If you run a Toyota and want to go slower then a dual t-case setup may be the answer you’re looking for.

There are lots of different adaptors and gear sets out there, everybody has to decide how they want to get to there desired crawl ratio, after a lot of reading, questions and internet chat room discussion, I decided Marlins dual transfer cases was the route I needed to take.

Here’s a quick look at what we’re talking about.

NOTE: Adding a second transfer case reduction unit using Marlins adapter lengthens your tranny/t-case assembly by 6 5/8 “, requiring the lengthening of your front driveshaft and the shortening of your rear drive shaft. Most of you probably know that drive shafts are “timed”, so when you get them back from the shop if you haven’t already done so you should mark it so that when you install u-joints etc. you can match the splines in the timed position.

Because Marlin has a great staff, great product and good instructions there’s no need for me to repeat what’s already written. Rather I’d like to provide an overview, some pictures and some “heads up” tips for the difficult sections. So here goes.

First make sure you’ve got all the parts, including seals that may be leaking, a clutch that needs replacing etc., cuz you’re going to be there anyways. After getting your parts, including that all important donor transfer case and adapter, go ahead and assemble your crawler unit before parking your rig for a day or two.

Here’s the Toyota gear reduction unit that you get from your donor t-case (on the left) and the mating surface of the Marlin adapter on the right.

Starting from left to right with the red circles I’ll mention some pointers.

• Install the FIVE studs provided with the adapter using blue locktite, short threads into case.
  
  NOTE: You’ll have ONE empty threaded hole at the very top center of your case, DON’T put a stud in there.
  
  
• Make sure the 4WD shifter rod assembly is removed and the plug provided is installed in the side of the case with some sort of sealant. You can’t see it in this picture but make sure you weld the tab onto the 2WD shift fork so that the shifter is captured.
  
• Make sure to put a lubricant (grease or gear oil) on the small needle bearing on the input shaft. This bearing will end up inside the new shaft Marlin provides.
  
• Don’t forget to install the drain plug from your donor case in the bottom of the adaptor.
  

The output shaft on your donor box may need to be slightly modified with a grinder. The new shaft that Marlin provides should be able to slip on (like the picture below). Remove material that would restrict this, make sure to protect your bearings etc. from the grinding dust and small particles of metal.

Once you’ve got these mods done it’s time to make the donor reduction box and the adapter one piece. Remember to lube all the parts so that everything can spin up with oil on it. Don’t forget the ¼” ball bearing that locks the spacer in place on the new Marlin shaft! Also make sure that the heavy duty snap ring is seated on the new shaft.

NOTE: Once you have the gears lined up properly the two cases should slide together without any force. Make sure and use your favorite glue between the cases- you don’t want an oil leak!

Okay you’re ready to drop your tranny assembly from the rig now. Good time to get a friend, one that likes lifting weights, or perhaps a friend with a tranny jack! Once the basic deed of getting the assembly out from under the rig, you may want to take the time to clean it up. Mine was a mess, with a couple of shot seals and some other issues it needed a cleaning bad.

Yes, that’s a can of degreaser. A wire brush, scraper and high pressure washer and an hour or so later it looked much more presentable. If you haven’t drained the oil in your t-case (I forgot to) when you separate the t-case from the tranny you will have an oil slick.

Once the two are split you want to replace the rear seal with the one supplied in Marlins kit and then glue a gasket on the back so you can mate your new extra t-case up to it.

Once you’ve got that taken care of, install the six studs provided using loctite onto the front of your old t-case, glue a new gasket on and bolt the two together.

• If you ordered the speedometer extension, now’s a good time to put it on.
  
• Don’t forget to splice in 6-7” of wire in your 4WD indicator wire if you want to light on the dash to work.
  
• This is also a great time deal with that pesky t-case cross member. Marlin sells a beauty for about $200. I fabbed one with dual mounts from a piece of steel I got at the junk yard.
  

We mounted the tranny & t-case assembly to the cross member loosely and then installed the whole thing. You’ll need to modify the tunnel and we ended up making a really funny looking custom shifter for the t-case from an old 3/8” drive extension. You’ll figure it out. Here’s the goal.

Make sure you put oil in the tranny and new t-case assembly. Your transfer case takes 3 quarts of oil now with the extra gear reduction and adapter. Have fun.