By Dallas Wiebe (2caseB2)

‘A-case’ refers to the reduction unit you will be building

It is not an impossible thing to build your own dual transfer case setup using mostly stock parts.  I started with a BW1354 electric case that I got from the wrecking yard as a core for $60.00 (can). I put this custom case between a C5 automatic transmission and a BW1350 transfer case. The transmission and the rear transfer case were unmodified except for a sharp elbow on the transfer case vent and a slight notch in the trans adapter to clear the A-case shifter cable.  The transmission and dual case assembly ended up being only 1-1/2″ longer then my original A4LD – BW1350 setup, although it still requires driveshaft length changes.

Now to build the A-case (the reduction box)  

I started by by splitting the core case at the factory split down the middle.  You want to keep the front half (with the planetary and low range shift fork). The chain, the rear case half and all the 4wd shifter mechanism isn’t needed.  The factory split point on the rear of the front case half is of coarse nice and square, we need to adapt this to the front of the stock rear case.

I sawed off extra chain case area of the front case half, leaving enough area to work a shifter fork and a cable engage mechanism.  I used 1/2″ aluminum plate to enclose the chain area and make the back of the A-case.

The bolts that hold the front of the transfer case bearing retainer to the case body must be removed and drilled all the way through the case and the rear 1/2″ plate (which needs a very round hole in the middle which fits snuggly on to the front of the rear transfer case).  A long ready rod goes through the whole thing and threads into the bolt holes of the bearing retainer of the the rear transfer case.  Each of the four rods have two nuts, one at the front of the A-case bearing retainer and one at the front of the rear case bearing retainer.


These four rods and one bolt inside, near the shifter fork area were the chain used to run, holds the A case together and holds it to the rear transfer case. I got the machine shop to build the A-case output shaft by joining an old trans output shaft to the front section of the original A-case main shaft.


The shaft was made by boring the A-case stub out and using 50 tons of pressure  to press the machined trans output shaft into the middle.  Using the custom A-case output shaft for alignment I stacked the A-case on the Rear transfer case with the 1/2″ adapter plate between.  The adapter plate was already drilled for the ready rod, the alignment dowel pin, and had a well fitting 4-1/8″ hole in the middle (hole saw a die grinder and lots of patience).  With these pieces all aligned I welded the A-case to the adapter plate.  Yes you can put all the A-case guts in from the front.

After welding plates over the opening in the side where the chain used to run I had a basic case built.

Note- I am not a professional aluminum welder, but I had a very hard time getting a good bead between the cast aluminum case and the aluminum plate. I am told this is because of the very high magnesium content in the cast case.

To shift this beast………

The rail that the shifter fork rides on must be shortened and a hole must be drilled in, but not through, the rear 1/2″ adapter plate.  The shifter fork was modified to accept the end of a vacuum operated shifter cable as used in a Chevy S-10 front differential lock.


A hole was drilled in the front of the A-case and a fitting was tapped and sealed into place which would accept the S-10 cable housing.  A spring, which used to be on the other side of the shift fork, was placed between the front inside of the A-case and the shifter fork.  The fork was ground down a little so the spring goes over the area where the shifter rail goes through the fork.  The spring of coarse moves the shifter fork in the opposing direction of the vacuum cable.  The vacuum pot was screwed to the firewall and is operated by an EGR vacuum solenoid used in carbureted operated Rangers and the like. The rear case shifter will have to be secured to the side of the A-case and modified to reach your stock shifter hole (If you use the A4LD 4×4 shifter your only 1-1/2 inches short).


There is lots more little stuff to it, like drain and fill plugs, a vent, and actually getting the dang thing to hold oil.  But if your into this kind of fabrication these things are fairly obvious to figure out.

UPDATE 05/11/2002 – From 2caseB2

The shaft between the 2 cases which was made form 2 pieces pressed together snapped. Shaft needs to be made of one piece.

UPDATE 07/16/2002 – From 2caseB2

The input shaft for the dual case did break, I just welded the stub onto the input of the second transfercase. It is stronger than before and is still working, but if the input brg. of the second case ever goes I’m screwed because the shaft I welded on is bigger than the id. of the brg.  The machine shop wanted over $500 to make a hardened shaft from scratch with no warranty, so for that price I can buy 10 transfercase input brg assemblies.  So It is still working great but it is not in the bolt on department in any way shape or form. Bottom line, hard to make, marginal strength, leaks a little oil, AND ROCK CRAWLS LIKE NO TOMORROW!!

To spline the shaft would be a good idea, but they are actually hollow, once the shaft was machined to the correct diameter it would be very thin wall.  Interesting point is that the shaft didn’t break back into the two pieces, but instead broke just where the spline on the small part of the shaft ended.  The actual press fit between the 2 pieces didn’t slip.


More Articles: