Dana 300 transfer case rebuild and flip

This Dana 300 transfer case will be the final stage behind a Toyota reduction box through a couple of adapters. The best part about this case is it's ability to shift the 2 axles independently. i.e. a shifter for each axle that can go low-neutral-high range. This gives me "turn'n'burn" ability, locking the rear axle and using the front to drag the nose of the truck sideways. This is just one little trail trick that can be done with this setup. The following steps were taken to flip the case for a passenger side front drive shaft. The mounting of this case makes rotating it fairly easy allowing me to get it up flat against the floor for max clearance.

The final setup:

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Marlin Crawler adapter info(#27-AT)     OTT D300 adapter info

 

I started disassembly by removing the countershaft and gear. Just make sure you get all the goodies that are going to fly once it's all loose. The shaft is held in place by a bolt down tab on the backside of the case. Note there is also an O-ring on the shaft too.

With the counter gear out of the way you can get to the allen setscrews that hold the shift forks to the shift rods.



With the forks released the front output/shift housing can be wiggled out. The long rear fork needs to be flipped over. The short fork will just swing up into the new position.



With the front shift rod pushed in to it's last detent, the rear rod can be worked out. Be ready to catch the detent balls and springs as the shafts are pulled.



Next we extract the lockout pills. They just won't fall out the shift rod bores, you have to knock out 2 little plugs to let them out. The plugs are a soft aluminum sitting on a step in the hole. I used a flat punch about half the diameter of the plugs to just drive them through. Then shake accordingly.

And now we get creative. The shifter housing and front output housing need to be surgically seperated.


The first cut is on the machined side but I only went as deep as the flange shown by the arrow. The yellow box shows the area I'm trying to save, it's the pockets for the detents. If the pockets die I have a back-up plan.



These shots show how i took the perpendicular cuts as close as I could to the detent pockets.



After my Sunday power nap I decided the only way to cut all the way was with a second cut at 45deg to the original. As you can see I only shaved the very bottom of one of the detent pockets.



A little chunk of tape and some JB Weld takes care of the exposed detent pocket. And the plug holes for the lock pill removal are drilled and tapped for 1/4" pipe plugs.



Driving the big gear and rear bearing off the front output shaft so I can get them all the way out. Then I pulled the rear output housing. I only use the puller to put some pressure on things then hammer the puller bolt, take up the slack, hammer again, take up the slack.....



Now carefully extract the %#&)*#$%#@^% pressed in factory vent since it will be in the wrong place. It's hole gets tapped for a 1/8" pipe plug, no drilling needed.



Popped the shift rod cups out. (almost fell out) Found some 3/4" brass freeze plugs to cap the holes.



I bought 4 of the 3/4" freeze plugs but the front holes were a little smaller, they fit now. Some bling saftey red bakin' in the halogens.  Mmmmmm, bacon.
Also notice I've rounded all the sharp edges where the casting has been machined. FWIU this reduces "stress risers" in the casting reducing the chance of a crack starting. Does it work, I donno, but why not at this point.



Here I'm using some straight edges to help align the cover. Then I placed the partially built adapter in position and used transfer punches to mark some holes. With a couple bolts in place and the all the input/output shafts in place I can guesstimate where the shifter housing is going to land. With the forks engaged with the collars I slide everything towards the input/rear output end (yellow) leaving it on the original case housing (green) then mark the position. (blue) When I actually drill these holes they are centered on the square tube vertically, this is so the forks are not bottomed in the collars as they were when we marked the holes.



Ok, with the holes drilled on the front part I can temp. assemble and check one last time. When I'm happy with the shifter housing position it's clamped and I use my transfer punches to get it aligned accurately. Once the front end is done the rear section of the adapter can be welded on. Then the shifter housing bolted on to mark the backside shift rod holes. Note: All the holes going through the adapter for the rods are drilled oversize to allow for "adjustment"



Things are starting to take shape. I welded in some 3/4" steel tube for the back end of the rods, this was tricky and took lots of cross tacking to control warping. With a little filing the rods worked smoothly. Then I just brazed some sheet metal caps on them. Now everything goes back in the case to fit the forks. With the detents in the middle on the rods (neutral), put the forks in the neutral position, check your slop at the collars making sure it's even on both sides, then lock them with the original setscrews. (the one for the front sucks, it's upside down) Then with the forks attached, it all comes back out and new holes from the top are drilled. I start with a pilot hole making sure I do go into the rod a little to start the new setscrew divot.



The forks were drilled and tapped for 3/8-24 for the setscrews and the divots are made with ~3/8" drill bit.
The adapter is finished for paint. notice a few things were added: a case vent tube, a tube for the top end of a sight level gauge, shift housing studs welded in, and oil deflectors.

Here you can see it's starting to look whole again. All new seals are installed along with a new input shaft bearing. Sorry I've missed a few photo steps here but if you've made it this far it shouldn't be an issue.

On the right is the electronic speed sensor that adapts to the original D300 mechanical speedometer drive. It's from Dakota Digital part# SEN-01-1 . This sensor is interfaced to the engine/transmission control with the SGI-5 also from Dakota Digital. The SGI-5 was originally purchased to compensate for tires and gearing and a perfect candidate for the upgrade.

The final product behind a Marlin Crawler reduction box made possible by an adapter from OTT.

So I get this box from Marlin today:

Weee, time for box 2! On to Toyota reduction box assembly.

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