My 4runner’s dual transfer cases exploded on the highway

As I was heading from Monterey to Forked Meadow with my built 1986 Toyota 4runner, the transfer cases ripped themselves apart outside of Los Banos on the highway. The truck went from running fine to everything is broken in about 30 seconds. I was able to limp into a pull-out and get a tow truck to take me back to Monterey. I had the truck dropped off in a friend’s driveway so I could start repairs.

Upon closer inspection, the adapter plate (a very early Marlin Crawler / Advance Adapters dual transfer adapter plate) had ripped in half and the rear drive shaft’s double cardan joint had destructed.

I called up Marlin Crawler and Advance Adapter to discuss the situation. Neither had heard of a transfer case adapter plate tearing in half like this. After calling around to the various companies who make adapter plates, I ended up ordering a replacement from Advance Adapter because they actually had it in stock and could ship soon versus other companies that were quoting 8-12 weeks before one would be available.

The damage to the truck is pretty impressive. But interestingly the gears and bearings are perfectly fine with zero damage. It was just the aluminum transfer case adapter and one of the aluminum t-cases that broke. Plus the double cardan joint. And also the Sky MFG driveline e-brake took some damage. I wonder if the driveline e-brake could have caused the problem to begin with.

I ran into some fitment issues with the new coupler and the 4.7:1 Marlin Crawler full length spline gears in the rear t-case. Design changes in the new adapter plate from Advance Adapter means that it doesn’t fit full length splines on the rear t-case input shaft. The options I had available were either to 1) buy an adapter from Marlin Crawler, 2) buy 4.7:1 gears from Advance Adapter, or 3) grind off material on either the adapter or the input shaft. I chose the last option and set to work grinding off some material on the input shaft. If I had anything other than an anemic 22RE motor, I would not have chosen this option. At some point I’ll be getting back into this t-case to do something different with this configuration because I’m a bit worried that this is the new weak point on the entire drivetrain now.

I got the t-cases back up into the truck and installed the new driveline from South Bay Driveline. I told them to pick a fun color so I got teal as a result! Looks great!

While I was working on everything, I decided to inspect the rear axle to see if any damage happened to the differential or the axle outers. I did replace some seals but the bearings were all good. The gears looked great. I’ve got a suspicion this axle has a slight bend somewhere that misaligns everything ever so slightly.

In the end, it took me from mid February until mid June to repair most everything. I still need to come up with a new e-brake solution (that old driveline e-brake never worked right), I discovered damage to the fuel lines that needs to be repaired, and the hard lines for the brakes on the rear axle need some attention. I’m out of energy to do that work so I might end up seeing if the local 4×4 shop is willing to take on those projects. Someday this truck will be back on the road…