Samurai Transfer Case Spine



In anticipation of installing a set of the new 8:1 gears in my Samurai transfer case I set out to reinforce the mounting system and find a way to spread the loads on the case itself out amongst more than just the stock 8 mounting bolts. 

I decided to give the case a spine.  First I made a cardboard template using the middle section of a Samurai t-case.  The plan was to make a plate that had 8 mounting tabs to hook into 8 of the mounting bolts that hold the case together.  The plate would then be bolted to a pair of blocks, one on the short side mounting arm and one on the long side.   The spine was cut from 3/16 steel by my friend Scott at A-1 Fabrication.  Scott is a wizard with anything involving sheet metal or welding.

I left excess material along the top and sides with the plan of whittling it down to get a close fit.  Once I had transfer punched and drilled the holes in the spine, I attached it to the transfer case.  Next I test fit in into my rig.  There were a few interferences.

After several more test fit/grind operations, this is the shape I ended up with.  I also used a hammer to clearance the transmission tunnel corners slightly, nothing really noticeable from the inside of the rig.

Once I knew I could slip the whole assembly into position under the rig, it was time to fabricate the mounting points for the spine and transfer case bucket.  On the short side I welded a block to the meaty part of the arm, transfer punched the holes from the spine and then bolted it to the spine.  I could then weld it.  It's very important to have everything bolted together before welding to avoid any warpage due to heat.

In the first picture you'll notice the two case bolts are recessed approximately .31" back from the other case bolts. I simply made two small mounting tabs about 2" long, drilled a hole, then bolted them to the case.  Next I made two small 1" spacers out of 1/8" material, slid the spacers between the spin and mounting tab, then welded the three pieces together. The second picture shows the mounting tab that I welded to the long side arm for the spine.  I also reinforced the section of the long side that transitions from thin material to thick material near the transfer case mounting flange.  Once again I bolted everything back together before welding on the bucket with the exception of the small reinforcement plate.  Unfortunately the bucket warped slightly so I ended up having to cut the short side mount off, bolt everything together and then weld the short side arm back on.    I think if you do 1" beads and then let the bucket cool you could avoid this. 

Here's the completed case complete with spine. 

You'll notice I also drilled and tapped the PTO mounting holes on the backside of the transfer case for M8 x 1.25 mounting bolts.  I then added an arm that bolted to the short side arm and wrapped up and around to grab two of the PTO mounting holes.   This was done when I was having problems with my case bolts working loose.  It did stop the short side case bolts from working loose as often as they did but it didn't seem to do much for the long side.  The ultimate solution was to replace the back half of my transfer case or helicoil the mounting holes since the threads had been flattened out from the bolts working loose.

Update 11-04

After several months of hard usage I believe the t-case spine did what I wanted it to do.  I did not have any more issues with the t-case bolts working loose and the case itself held up to some fun full throttle assaults at the Avalanche Ranch, a trip to johnson Valley and many trips to local trails.  I think the biggest downfall of the divorced t-case in the Samurai is the fact that as the chassis twists, some of that twist is also transferred thru the t-case, with the spine tying both sides together I think the t-case did see less distortion.