Trail-Creeper TM  Dual Transfer Case
Install Instructions
 

Dual Adapter   Dual Adapter Parts List:
  • 23 or 21 Spline coupler
  • Adapter plate with bearings installed
  • Bearing spacer
  • 11 Studs and nuts
  • Drain plug
  • Rear transmission output seal
  • 2.28 Shift knob
  • Snap Ring
  • Shifter keystock
  • Detent plug
  • Three paper gaskets
 

 

Tools Required:

  • Ratchet, 12mm, 14mm, and 30mm sockets
  • Air Wrench
  • Needle Nose Pliers
  • Hammer
  • 3/16 Diameter Pin Punch
  • Snap Ring Pliers
  • 6mm Allen Wrench
  • Gasket Scraper
  • Flat Blade Screwdriver
  • Adjustable Wrench
  • Locktight thread locker
  • Axle Grease

 

 

 

 

What is the difference between 21 and 23 spline gears?

The transfer case input gear is the gear that slides in to the transmission. V6 and Turbo transmission use a 23 spline gear that is slightly larger then the 21 spline gear used on 4cyl transmissions. On a single transfer case you must use the gear type that matches the transmission.

If you are building a dual transfer case assembly, the front case input gear must match the transmission output gear. The rear case of a dual transfer case can be set up with either 21 or 23 spline gears. When purchasing a dual transfer case adapter you can choose to purchase a 21 or 23 spline version. The only difference between a 21 and 23 spline dual adapter is the coupler that connects the front and rear case. It is important to match the dual adapter and rear gear set. If your rear case is going to run the stronger 23 spline gears you must also run a 23 dual adapter coupler. If your rear case is going to use 21 spline gears then the dual adapter coupler must also be 21 spline.

In a dual transfer case with 21 spline gears in both cases the weak spot and most common failure point is the input gear to the rear case. A dual transfer case built with 21 spline gears in the front case and 23 spline gears in the rear case is stronger and now the most likely point of failure becomes the rear output shaft. If your purchasing both a dual adapter and 4.70 gears for the rear case, order both in 23 spline. There is no cost difference building with 23 spline parts if you order both the dual adapter and gears in 23 spline configurations.

If you have questions about setting up your gears or dual adapter, please call us at 559-252-4950.

To build a dual transfer case crawler you will need most of the parts that make up high/low section of a gear-driven Toyota transfer case. Below is a photo showing the factory parts that you will need from a stock case.

 

 

 


 Step 1: Weld the provided key stock to side of shift fork as show above. This prevents the front transfer case shifter from going side to side and only allows it to shift front and rear.

Step 2: Using a brush, apply axle grease to the base of the coupler.


Step 3: Slide the coupler bearing over the coupler.

Step 4: Grease the coupler bearing.


Step 5: Slide the 2.28 low speed gear over the coupler bearing.


Step 6: Slide the provided bearing spacer on to the coupler, above the low speed gear.

 


Step 7: Hold the bearing spacer with one finger and flip the assembly upside down. Slide coupler (with spacer, bearing and low speed gear) in to place on the dual adapter as shown above.


Step 8: Turn adapter over so that the coupler is under the adapter. Apply provided snap ring to coupler.
 


Step 9: Turn dual case adapter over so that the low speed gear previously installed is again facing up.


Step 10:  Place collar into shift fork groove.


Step 11: Slide high/low shift rail, fork and collar on to coupler. Note position of the shift rail going into the dual adapter.


Step 12: Fully seat the shift fork assembly on to the low speed gear. This may require turning the shift hub slightly.

 


 Step 13: . Apply grease to the dual case needle bearing.


Step 14: Install counter shaft in to adapter plate needle bearing.


Step 15: Grease pocket bearing from original transfer case.


Step 16: Install pocket bearing in to coupler.


Step 17: Slide input gear in to coupler pocket bearing


Step 18: Seat input gear all the way down so that it meshes with the counter shaft gear.
 

 


 Step 19: . Place gasket on to face of dual adapter as shown.


Step 20: Install five of the new studs in to empty reduction housing.


Step 21: Slide reduction housing on to dual adapter plate.


Step 22: Install two stock bolts in passenger side of dual adapter


Step 23: Install nuts and tighten


Step 24: Slide snap ring in to place over counter shaft bearing.

 

 


 Step 25: . Install snap ring over input gear bearing.


Step 26: Place original detent ball in to hole on passenger side of the dual adapter.


Step 27: Place original detent spring in to hole on passenger side of the dual adapter.


Step 28: Place a drop of lock tight on to detent ball plug and install in to adapter using Allen wrench.


Step 29: Install drain plug and gasket (provided with kit) in to bottom of dual adapter. Tighten using 10mm Allen wrench.


Step 30: The shift rail that was located on the driver side of the reduction housing is no longer used. Install provided plug in to the driver side detent hole. Apply Locktight to threads to prevent plug from coming out.

 

 


 Step 31: . Your crawl box is now ready for installation on your transfer case.


Step 32: Install six studs (provided with kit) in to the face of the rear transfer case.


Step 33: Two gaskets are provided for mating the front and rear units together. Choose the gasket that best fits your model of t-case. Slide gasket over studs previously installed in to rear case. Slide front dual case on to studs in rear case until the mating surfaces contact. Install nuts to connect cases together.


 

 

Gasket Warning: Please use only Trail-Gear provided or factory Toyota gaskets. You can easily tell the Toyota gaskets as they have green lines on one side. Some aftermarket gaskets do not have the proper oiling holes. Use of these gaskets in any dual adapter will result in failure, sometimes in as little as 5 miles. The result of this failure is that the bearing melts down and the drive train suddenly locks up after just a few miles of driving. This could easily cause an accident. Please don't use gaskets you have hanging around your shop or gaskets from other brand kits, unless you see the factory green stripes.
 

After installing transfer case, use the rear fill plug and fill transfer case(s) with 80/90W GL5 gear oil. Once oil starts leaking out of the fill hole, the transfer case case is full. Transfer case oil should be replaced after 1,000 miles, then at every 30,000 miles thereafter. Conventional or synthetic oil may be used.

These instructions are designed as a general installation guide. Installation of Trail-Gear Products requires specialized skills such as metal fabrication, welding and mechanical trouble shooting. If you have any questions or are unsure about how to proceed, please contact our shop at 559-252-4950 or seek help from a competent fabricator. Using fabrication tools such as welders, torches and grinders can cause serious bodily harm and death. Please operate equipment carefully and observe proper safely procedures.

Rock crawling and off-road driving are inherently dangerous activities. Some modifications will adversely affect the on-road handling characteristics of your vehicle. All products sold by Trail-Gear Inc are sold for off road use only. Any other use or application is the responsibility of the purchaser and/or user. Some modifications and installation of certain aftermarket parts may under certain circumstances void your original dealer warrantee. Modification of your vehicle may create dangerous conditions which could cause roll-overs resulting in serious bodily injury or death. Buyers and users of these products hereby expressly assume all risks associated with any such modifications and use.

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