Full-time 4wd conversion: NP241 to NP(NVG)242

[MPrichard]

I'm trying to figure out how complex it will be to drop a 242 (switchable full-time) transfer case into my '93 burb. The easiest ones to get are out of Jeep Grand Cherokees, and these also have the 2wd option which the Hummer ones don't, and that's a requirement. I know the max. torque ratings are lower, but I don't tow often, and only small trailers when I do (<3k lbs.) I'm wondering if I can mix and match compatible input and front shafts from a donor 241 which appears to share many of the same seals/bearings and shafts. Obviously the tailshaft (and housing) may require a rear driveshaft slip joint mod if I can't find one compatible with the GM one. Or should I just focus on getting the HD version out of a Hummer which may (should?) bolt-up, and then trying to add the 2wd mode to it?

Any insight would be welcome. It doesn't look like anyone's every done this, at least according to google, and that surprises me given the huge driving advantages to full-time when driving on mixed surfaces (snow/ice/dry) and making sharp turns on trails without binding the hell out of the driveline.

[HH]

Might want to check on the pirate 4x4 board. Most of the NV TCs are similar and some parts will interchange.

[MPrichard]

Thanks. I've pretty much combed the web out of info and have learned a lot about the case, mostly from the various Jeep groups. Sadly, there's a general pre-disposition against full-time t-cases in those groups, so it takes a bit to separate the real info from the chaff. I don't know why part-time cases ever became popular (other than cost) as they're so limited in usability. What's the point of lugging all of that 4wd hardware around if you can't enjoy the benefit except in the vary worst snow and off-road? The vast majority of 4wd vehicles in use today, I'd warrant, are frequently driven in the rain and/or slush (where part-time isn't usable) but only rarely off-road or in deep snow. It's crazy that all of those AWD mini-vans and cars are enjoying better traction and stability than most 4wd trucks and SUVs, most of the time.

The 242 offers the best of both worlds with 2wd as well as full-time 4wd, and when things get really sticky, 4wd-locked. I've noticed that the Hummer H1, Unimog, G-class, many Landrovers and some Land Cruisers all have lockable full-time t-cases, in addition to the few Jeeps/Dodges with the 242, so I'm surprised (and annoyed) that GM/Dodge/Ford gave up on full-time in their full-size vehicles after the NP203 from the 70s. I know that there are some weird electronic or viscous pseudo-full-time cases like the 247 and 249 (or 267?), but it doesn't look like these actually have a differential in the center, just some clutching contraption for "on-demand" 4wd.

Sorry for the rant, I'm just annoyed that I had to blindly blow $200 on a 242J to rip it apart and see what would fit from my 241, and after much reading and piecing together, it looks like I'll be able to use a 242 case with some (hopefully) minor drilling of transmission/t-case adaptor mounting holes (GM 241 clocked differently by around 5-10 degrees from Jeep cases), swapping in the 241 planetary and input shaft as well as the front shaft "yoke", replacing the rear slip yoke with a slip yoke eliminator kit and modifying my rear driveshaft to add a conventional slip yoke and mounting flange. We'll see if I can fit the larger chain/sprockets and what fabbing I'll have to do to get the GM speedometer sender into the Jeep case, or use one of those all-purpose electronic sender/ratio adaptors with the standard Jeep sender.

If anyone has any information on the encoding specs (pulses per rotation) of these various senders, that would be very helpful.

[93GMCSierra]

I understand your frustration, though I have been of only use 4x4 when needed variety I did have a 77 chevy with the fulltime 4 and like you say rain slush or just bad roads that gave great traction without the lurching that the part time gives on turns.