Thought I'd share some info on how to Twinstick a T-case for independent axle operation by grinding shift rails and therefore still maintaining the interlock. Bronchole this doesn't really fit in your Dana-20 sealing thread, not sure if this info will be useful to you.
There's several write-ups on how to do this (Ref-1, Ref-2). It takes a bit to orient yourself with how the shift rails travel and the relationship to the interlock pins & detent balls. The guiding principal here is that each interlock pin must have at least one end in a pocket on a shift rail at all times to operate correctly. You cannot move (shift) a rail into a position that will result in at least one side of an interlock pin not sitting in a pocket. This is how the interlock system works and prevents you from shifting into undesirable combinations such Front-Low + Rear-High.
When you twinstick a T-case, some folks simply remove the interlock pins allowing each rail to shift as instructed. Obviously in doing this you remove any safeguard preventing undesirable combinations. As an alternative, you can maintain the interlock safeguard by modifying the rear shift rail to allow for independent operation but continue to have interlock safety preventing the undesirable combinations.
[Side Affect] When you remove the interlock pins or grind the rails to allow the pins more movement, you introduce an undesirable side affect that can result in Rear-Low popping out of gear. This is due to the way Low Gear detent ball pocket on the rear shift rail is notched from the factory with a ramp allowing easier movement. Under stock configuration, one of the interlock pins nestles into a pocket on the rear shift rail which when combined with the detent ball keeps the TC in Rear-Low without issue. The side affect here is that the grinding required to allow independent axle operation modifies the interlock pocket essentially removing the interlock from helping to keep the rail in Rear-Low. As a result the detent ball has a tendency to "pop" out of its pocket due to the ramp. The way to overcome this is to add on material (weld) to the Rear Low detent ball pocket essentially removing the ramp and making a nice solid pocket instead. See pics 7 & 8 for this modification.
First a little familiarization with the shift rails. In each pic, Front axle rail is on the left, rear axle rail is on the right. Interlock pins are in the middle, pin 1 is on the top, pin 2 is on the bottom. Detent springs and balls are on the outsides and control which gears are selected on both rails. High gear is on the Top, Neutral is in the Middle, Low gear is on the bottom.
Original Stock Rails
First lets look at the original stock rails. Looking at the rear rail (right) you can see that two original interlock pockets exist. You can also see in black sharpie where I ground in order to expand those pockets.
On to the modified rails:
Pic-1 Neutral
In this pic you see both axles in the neutral position. Notice the detent balls are in the Neutral pocket on each rail. Notice both interlock pins have at least one pocket to rest in.
Pic-2 Front High, Independent
In this pic you see the front rail has shifted into High gear with the detent ball nestled in its pocket. This forces Interlock pin #1 out of the inside pocket on the front rail and into the newly ground pocket on the rear rail. Creating this pocket on the rear rail has allowed for this combination where it doesn't exist in stock form. In this combination the rear rail can only be shifted into 2 positions, either Neutral (as pictured) or Rear-High. It is not possible to shift the rear rail into Rear-Low as interlock pin #1 would have to overcome the ridge on the rear rail between the two inside pockets (remember each interlock pin must have at least 1 side in a pocket at all times). Interlock pin #2 is irrelevant in this combination as it always resides in a pocket on the Front rail.
Pic-3 Front Low, Independent
In this pic you see the front rail has shifted into Low gear with the detent ball nestled in its pocket. This forces Interlock pin #2 out of the inside pocket on the front rail and into the newly ground pocket on the rear rail. Creating this pocket on the rear rail has allowed for this combination where it doesn't exist in stock form. In this combination the rear rail can only be shifted into 2 positions, either Neutral (as pictured) or Rear-Low. It is not possible to shift the rear rail into Rear-High as interlock pin #2 would have to overcome the ridge on the rear rail between the two inside pockets. Interlock pin #1 is irrelevant in this combination as it always resides in a pocket on the Front rail.
Pic-4 Front & Rear High
In this pic you see your typical Front & Rear High. Both interlock pins have at least one end in a pocket.
Pic-5 Front & Rear Low
In this pic you see your typical Front & Rear Low. Both interlock pins have at least one end in a pocket. With stock rails, interlock pin #2 would help lock the rear rail into Low. However since the inside pocket was expanded to support independent operation, pin #2 no longer provides that support. As a result the detent pocket for Low on the rear rail was modified (see additional pics below).
Pic-6 Rear rail grinding
This is the expanded interlock pockets on the inside of the rear rail. The ridge in the middle prevents one axle from being in a High gear while the other is in a Low gear.
Pic-7 Rear rail modification to Low Pocket
This is the rear rail detent ball pockets. You can see where material was added to the Low pocket to remove the ramp, then ground smooth to make a nice pocket for the ball to rest in.
Pic-8 Rear rail modifications
Here's a top view of both rear rail modifications. The grounded out and expanded inside interlock pockets (bottom) and the modified/removed ramp for the Low detent pocket (top).
There's several write-ups on how to do this (Ref-1, Ref-2). It takes a bit to orient yourself with how the shift rails travel and the relationship to the interlock pins & detent balls. The guiding principal here is that each interlock pin must have at least one end in a pocket on a shift rail at all times to operate correctly. You cannot move (shift) a rail into a position that will result in at least one side of an interlock pin not sitting in a pocket. This is how the interlock system works and prevents you from shifting into undesirable combinations such Front-Low + Rear-High.
When you twinstick a T-case, some folks simply remove the interlock pins allowing each rail to shift as instructed. Obviously in doing this you remove any safeguard preventing undesirable combinations. As an alternative, you can maintain the interlock safeguard by modifying the rear shift rail to allow for independent operation but continue to have interlock safety preventing the undesirable combinations.
[Side Affect] When you remove the interlock pins or grind the rails to allow the pins more movement, you introduce an undesirable side affect that can result in Rear-Low popping out of gear. This is due to the way Low Gear detent ball pocket on the rear shift rail is notched from the factory with a ramp allowing easier movement. Under stock configuration, one of the interlock pins nestles into a pocket on the rear shift rail which when combined with the detent ball keeps the TC in Rear-Low without issue. The side affect here is that the grinding required to allow independent axle operation modifies the interlock pocket essentially removing the interlock from helping to keep the rail in Rear-Low. As a result the detent ball has a tendency to "pop" out of its pocket due to the ramp. The way to overcome this is to add on material (weld) to the Rear Low detent ball pocket essentially removing the ramp and making a nice solid pocket instead. See pics 7 & 8 for this modification.
First a little familiarization with the shift rails. In each pic, Front axle rail is on the left, rear axle rail is on the right. Interlock pins are in the middle, pin 1 is on the top, pin 2 is on the bottom. Detent springs and balls are on the outsides and control which gears are selected on both rails. High gear is on the Top, Neutral is in the Middle, Low gear is on the bottom.
Original Stock Rails
First lets look at the original stock rails. Looking at the rear rail (right) you can see that two original interlock pockets exist. You can also see in black sharpie where I ground in order to expand those pockets.
On to the modified rails:
Pic-1 Neutral
In this pic you see both axles in the neutral position. Notice the detent balls are in the Neutral pocket on each rail. Notice both interlock pins have at least one pocket to rest in.
Pic-2 Front High, Independent
In this pic you see the front rail has shifted into High gear with the detent ball nestled in its pocket. This forces Interlock pin #1 out of the inside pocket on the front rail and into the newly ground pocket on the rear rail. Creating this pocket on the rear rail has allowed for this combination where it doesn't exist in stock form. In this combination the rear rail can only be shifted into 2 positions, either Neutral (as pictured) or Rear-High. It is not possible to shift the rear rail into Rear-Low as interlock pin #1 would have to overcome the ridge on the rear rail between the two inside pockets (remember each interlock pin must have at least 1 side in a pocket at all times). Interlock pin #2 is irrelevant in this combination as it always resides in a pocket on the Front rail.
Pic-3 Front Low, Independent
In this pic you see the front rail has shifted into Low gear with the detent ball nestled in its pocket. This forces Interlock pin #2 out of the inside pocket on the front rail and into the newly ground pocket on the rear rail. Creating this pocket on the rear rail has allowed for this combination where it doesn't exist in stock form. In this combination the rear rail can only be shifted into 2 positions, either Neutral (as pictured) or Rear-Low. It is not possible to shift the rear rail into Rear-High as interlock pin #2 would have to overcome the ridge on the rear rail between the two inside pockets. Interlock pin #1 is irrelevant in this combination as it always resides in a pocket on the Front rail.
Pic-4 Front & Rear High
In this pic you see your typical Front & Rear High. Both interlock pins have at least one end in a pocket.
Pic-5 Front & Rear Low
In this pic you see your typical Front & Rear Low. Both interlock pins have at least one end in a pocket. With stock rails, interlock pin #2 would help lock the rear rail into Low. However since the inside pocket was expanded to support independent operation, pin #2 no longer provides that support. As a result the detent pocket for Low on the rear rail was modified (see additional pics below).
Pic-6 Rear rail grinding
This is the expanded interlock pockets on the inside of the rear rail. The ridge in the middle prevents one axle from being in a High gear while the other is in a Low gear.
Pic-7 Rear rail modification to Low Pocket
This is the rear rail detent ball pockets. You can see where material was added to the Low pocket to remove the ramp, then ground smooth to make a nice pocket for the ball to rest in.
Pic-8 Rear rail modifications
Here's a top view of both rear rail modifications. The grounded out and expanded inside interlock pockets (bottom) and the modified/removed ramp for the Low detent pocket (top).
