T-shift Dana 20 Exploded (edited)

T-shift Dana 20 Shifter Pill Modification

This isn't my photo - I collected these pics off the net for reference, but I'm not sure I'll be doing this mod.

Half the reason for rebuilding the t-case is that we can't get the shifter to move into 4H. When we had the body completely blasted, repaired, painted, & Rhino-Lined, the tunnel was completely closed up so the shifter hole could be cut precisely. But the guy in Baton Rouge who did some (crappy) work on the truck butchered it out worse than it was before.

This is half the reason for rebuilding the t-case; the shifter won't move into 4H, and it's an internal problem.

With the rubber bumper installed at the back of the crossmember, it's impossible to get to the lower L nut. And it takes a 4-way wrench to get to the middle L (almost visible above the upper shift rail).

The adapter required clearancing of the crossmember in several spots, and 1/2" of washers on each trans mount. See the NEXT pic...

Because I had installed the factory crossmember bumper, I had to lift the trans tailhousing (Advance Adapter) off of its mounts to access the lower L nut. But I'm not putting it back, so next time, it'll be fairly easy to drop the t-case.

I'm also replacing the stacked washers with a single shim on each side.

This t-case IS as simple as the schematics suggest. The front output gear (upper L) is centered, putting the front in neutral. The rear gear (upper R) is forward (down), putting the rear in hi-range (2H).

The Aluminum sleeve & stub shaft at the lower R are for the Advance Adapters kit for the AOD. Removing that shaft from the t-case allows about a dozen roller bearings to fall loose into & out of the t-case. Finding & re-installing them is a challenge.

Power comes in to the lower L gear from the transmission. The rear fork can push the rear output gear forward (for rear 1:1 high-range) or backward to engage the smaller central gear for rear low-range. If it's centered as shown, the rear is in neutral. The upper L gear is an idler spinning the same speed as the input, so the front (upper) output gear performs the same functions as the rear (lower) one.

But the pills between the shift rails prevent the front & rear from being in different ranges.

The output gear (lower R) is slid rearward on the output shaft to engage the smaller center gear (upper L) providing low-range.

The output gear (lower R) is slid forward on the output shaft to engage the splines of the input gear, providing hi-range.

With both output gears slid rearward, the t-case is in 4L.

The Aluminum sleeve & stub shaft at the lower R are for the Advance Adapters kit for the AOD. Removing that shaft from the t-case allows about a dozen roller bearings to fall loose into & out of the t-case. Finding & re-installing them is a challenge.

The front shift rail has position detents in its L side and pill grooves in its R.

The frear shift rail has position detents in its R side and pill grooves in its L.

This is the rear output gear.

This is the rear shift fork & rail.

This is the front output gear.

This is the front shift fork & rail.

4WD High
Both sliding gears (and the shift rails) are full forward, locking both outputs to the hi-speed (1:1)set of gears at the front of the case. The pills prevent the rear output shift rail from moving; only the front can move rearward to neutral.

The Aluminum sleeve & stub shaft at the lower R are for the Advance Adapters kit for the AOD. Removing that shaft from the t-case allows about a dozen roller bearings to fall loose into & out of the t-case. Finding & re-installing them is a challenge.

2WD High
The front output sliding gear is centered (neutral) and can only move forward (front high). The rear output is engaged to the input (1:1) and can move rearward to neutral.

The Aluminum sleeve & stub shaft at the lower R are for the Advance Adapters kit for the AOD. Removing that shaft from the t-case allows about a dozen roller bearings to fall loose into & out of the t-case. Finding & re-installing them is a challenge.

Neutral
Both sliding gears (and the shift rails) are centered, UNlocking both outputs. The pills prevent the front output shift rail from moving; only the rear can move either direction.

The Aluminum sleeve & stub shaft at the lower R are for the Advance Adapters kit for the AOD. Removing that shaft from the t-case allows about a dozen roller bearings to fall loose into & out of the t-case. Finding & re-installing them is a challenge.

2WD Low
The rear output sliding gear is full rearward (low-range). The pills prevent the front output shift rail from moving forward (to high) but allow it to move rearward to front (4) low.

The Aluminum sleeve & stub shaft at the lower R are for the Advance Adapters kit for the AOD. Removing that shaft from the t-case allows about a dozen roller bearings to fall loose into & out of the t-case. Finding & re-installing them is a challenge.

4WD Low
Both sliding gears (and the shift rails) are full rearward, locking both outputs to the small end (low range) of the center idler gear. The pills prevent the rear output shift rail from moving; only the front can move forward to neutral.

The Aluminum sleeve & stub shaft at the lower R are for the Advance Adapters kit for the AOD. Removing that shaft from the t-case allows about a dozen roller bearings to fall loose into & out of the t-case. Finding & re-installing them is a challenge.