Originally Posted by demuresjeep
I have the 94 zj and I was told by a mechanic that the trani was worn out and I would have to replace it. Okay, he failed to mention that it wasn't the original transmission, or that it was a trani off of a 4WD, not AWD. Went to a junk yard and low and behold there was a 94zj AWD sitting there with a good trani. Jumped on it pulled it out, got it home and began the work. Called in my uncle to help. we get both out and he realizes that these trani are not AWD. We stuck in the new one anyway and it works! Does any one have thoughts or advise on this?
The transmission is the same between 4WD and AWD - no real reason for it to be different. Any transfer case with the proper mounting will bolt right to it.
The transfer case is an auxiliary transmission that gives you 4WD/AWD capability (I believe the AWD is typically the NP249.) These may be swapped freely, as long as the mounting stud pattern and input gear are correct. There are a number of models of transfer case used across Jeep vehicles, with most of them in the last 25-30 years being made by New Process/New Venture/New Venture Gear (all the same company.) You'll usually see these listed here as "NPxxx" or "NVxxx", the "xxx" being the model number.
For instance, the "NP231" is a basic part-time four-wheel-drive transfer case with ranges of 2WD-4HI-N-4LO, and the 4LO range includes an extra 2.72:1 reduction step.
The "NP242" is a fairly basic full-time 4WD transfer case, modes of 2WD-4FT-4PT-N-4LO. The low range is 2.72:1 (as with most NP transfer cases,) and the "4FT" mode may be run on dry pavement for some time without binding - try that with a PT4WD case, and you'll blow the chain. And probably the case itself.
The "NP249" is, I believe, a typical AWD transfer case (no 2WD mode,) although I don't know that much else about it offhand.
- 4HI: This engages all four wheels as drive wheels, without an extra gear reduction step.
- 4FT: This is a 1:1 4WD mode that allows a 50/50 torque split between front & rear axles (to prevent binding in the case. I would typically use 4FT if I'm expecting foul weather or conditions, but I'm not there yet.)
- 4PT: Also a 1:1 4WD mode, this has a 52/48 torque split between front & rear axles, usually front-biased ("pull mode.") This allows for better steering control in 4WD, but this mode is not
to be run on dry pavement or firm surfaces!
- 4LO: A four-wheel-drive mode, 52/48 front-biased, that includes an extra gear reduction stage (increases drive torque/reduces drive speed.) Ratios on production cases have run from 1.85:1 through 4.0:1, with some aftermarket cases going even lower (I think the Atlas gets to about 4.2-4.3:1.) Also not to be used on dry/firm surfaces - and you'll blow up your case even faster this way! On-road, as a test, I won't go more than a half a block - just to make sure the mode actually works (realistically, I might
drive 100 feet on pavement. Maybe
- AWD: A fully-differentiated 4WD mode, which may be used anywhere
. The differentiation between front and rear outputs is the key here - similar to the differential in each axle (that allows the wheels to turn at different speeds without binding,) the differential in the AWD transfer case allows the axles to turn at different speeds - but is still set up to allow a very slight front bias (usually) to improve control. If you have a production AWD transfer case, you do not
have a two-wheel-drive mode.