Hummer NP242 Transfercase vs. Jeep
Updated April 15, 2009
This is going to be a continuing learning experience. It started because I was told that the Jeep has the same transfercase as the H1 Hummer. I also heard that the Jeep has a 2wd and possibly a low unlock which would allow you to drive in low gear without winding up the drive train when driving in places like Moab Utah where the slick rock is anything but slick. I was directed to a photo gallery by Michael Rollins who has allowed me to use his excellent photos on this site.
The hot setup for a Jeep is the Hummer transfercase due to it's increased strength. Michael has adapted the Hummer case to work in a Jeep. According to Michael The Jeep t-case (242J) has a 2wd position that disengages the front output. There are aftermarket companies that make a 2wd low kit for the 231 t-case. It should be possible by modifying the gear selector to make a 242J have 2wd low but I haven't done this.
The parts that allow for 2wd are the differential, shift collar, and selector. Basically inside the diff where the collar goes in has a clear area of splines. The diff housing on the collar side is also bevel cut to allow the collar to bottom out inside the diff. So when the collar is pushed all the way in it disengages the diff.
The photo gallery shows pictures of the parts and how the Hummer / AMG transfercase differs from the one used in the Jeeps.
I am still learning that New Venture is still changing this t-case. I just recently saw a KJ (Jeep Liberty) 242 apart which has yet other differences. It has a bigger 32 spline output with I think it was the smaller chain. These later t-cases also use a slip yoke that is greased and external to the case unlike older (on Jeeps 95 and older) which have a internally lubricated slip yoke like the modified AMG I have or even my original 88 242J.