Teraflex Manufacturing Dana 20 Low Range Kit

Part 2 of the Uber-20 project
(Building the ultimate low geared transfer case at home)
By BillaVista

Page 2 - Dana 20 Teardown Part 1

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Dana 20 Teardown

You're on your own for removing the Dana 20 from your vehicle, as there are endless possible configurations.  For example, here you can see my custom transfer case doubler removed from the Wolf and consisting of:

  1. NP 203 low range gearbox
  2. Custom machined aluminium doubler adapter
  3. Dana 20 ('79 Jeep CJ7 variety)
  4. Advance Adapters Dana 20 output kit

For orientation, the blue arrow in the pic indicates the shift rods of the Dana 20.

 

In my case, the first task was to separate the Dana 20 from the rest of the transfer case components.  From left to right we can see the NP 203 low range box, the doubler adapter, and the separated Dana 20.

This shot shows the Dana 20 input gear attached to the doubler adapter via the output shaft of the custom machined (shortened and re-splined) 203 output shaft.

In non-doubler installations, this D20 input gear will be on the transmission's output shaft.

Front view of the removed Dana 20
Rear view of the Dana 20
Right side view of the Dana 20
To begin the teardown of the transfer case, place it on a sturdy bench, upside down with the lower cover facing up, as shown here.
Begin by removing the bolts that hold on the lower cover...
...and remove the lower cover.

 

Inside the stock Dana 20 we have:

  1. Rear output shaft (in this case, not stock, but Advance Adapters 32 spline kit)
  2. Rear sliding gear
  3. Intermediate gear
  4. Intermediate gear
  5. Front output shaft
  6. Front sliding gear
  7. Front output gear

*not shown in this view is the main drive gear (input gear) which is still attached to the doubler adapter at this point (see above)

 

As above, from greater distance
Remove rear output shaft housing assembly.  Procedure is similar whether output housing is stock or aftermarket.
Once the rear output shaft assembly is removed, disconnect the rear sliding gear from the jaws of the rear shift fork (blue arrow)
Next,on the front of the case, remove the transfer cases tag (if it's still present) and the lock plate for the intermediate shaft.
From the front of the case, and using a brass or other soft drift, drive the intermediate shaft to the rear of the case...
...and then remove it from the case.
Wiggle the rear sliding gear out of the way (now that it is released from its shift fork) and then lift the intermediate gear from the case.
Be careful when removing the intermediate gear, as their are 3 silver bearing spacers (one on each side (blue arrow) and one in the middle seperating the 2 rows of needle bearings) in the gear that sandwich the large roller bearings.  Remove the gear, and then remove the bearing spacers and roller bearings and store them carefully out of the way. 
If you are not careful - and you drop or bobble the intermediate gear - this is what you get.
Once you have removed the intermediate gear, there will be 2 thrust washers left in the case (yellow arrows).  Make a careful check for any loose needle bearings still in the case (blue arrow)
Take note of the orientation of the thrust washers for reassembly time.  Each has a small tab (blue arrow) that indexes with a slot in the case (yellow arrow).
This shot shows the inside face (i.e. the side that faces towards the middle of the case) of the thrust washer.  This is the side that goes up against the intermediate gear on installation.
Once the intermediate gear is removed, you have room to reach in and wiggle out the rear sliding gear.
Next remove the nut retaining the front output yoke.
Remove the nut, washer, yoke and shim washer from the shaft and you are left with this.
Next remove the bolts that hold the front output housing to the case.

Tap or pull both shift rods to their centre (Neutral) positions. Next, remove the caps covering the detent balls and springs (also called "poppet balls" - these springs and round ball bearings are those that keep the shift lever(s) in the gear you select.)

I found the easiest way to shift the rods was to insert a small punch through the hole in the end and use it for leverage.

This shot shows the poppet ball and spring in relation to the housing.

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Contact Info:

Tera Manufacturing, Inc.

5251 South Commerce Dr.
Murray, UT 84107-4711
phone/801.288.2585 -- fax/801.288.2571

http://www.teraflx.com/

 


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