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Operating Your 4WD System

For Late Model FSJs

2WD > 4WD high and 4WD high > 2WD

Put the vehicle in neutral, flip the SelecTrac switch, and if the 4wd green lite doesn't come on, let off the brake. If that doesn't do it, put the vehicle in reverse, then neutral, then drive. By this time the vehicle should be in the desired drive mode. If not, try rolling it forward or back a tiny bit.

While driving
You can also shift to/from 4wd: I flip the switch after letting up on the gas, normally that does the trick, otherwise, shift into neutral. I've shifted anywhere from 0-55mph with no problem.

4hi > 4lo and 4lo > 4hi -- must be in 4wd already (see above)

Shift while moving 0-2mph and be quick about it. I prefer shifting stopped. If you grind, that's life — stop the vehicle, turn it off, leave in neutral and then shift. If you've got new fluid and you get some practice you can shift while slowly rolling or when stopped. Best not to be uphill or downhill when doing this or you're sure to have to stop and turn off and maybe let the vehicle roll a bit then stop and try again. If you shift and get the tcase in neutral instead of the range (lo/hi) you wanted, at this point you might as well shut it off to shift.

When to use 4lo or 4hi?
In 4hi you can drive on any condition of road, pavement, dirt, etc. Slick conditions such as snow or ice may warrant 4hi, if you need to maintain highway speed. Off road if the trail is smooth, flat, and wide where faster speeds can be safely achieved. Never drive over 25mph on a tight trail with blind curves.

Only drive 4lo off-road. Absolutely no dry pavement in 4lo!! Use 4lo for climbing and descending steep hills. The low gearing actually helps as a brake for descending steep inclines.

What is Selec-Trac and Quadra-Trac?
QuadraTrac is what Jeep called the Borg Warner 1339 transfer case (and the 1330-something whatever the one was with no lo-range). They also gave this label to the New Process 219. Both are full-time 4wd systems. The BW1339 uses a viscous limited slip that transfers powers from slipping wheels to gripping wheels whereas the NP219 I believe is just a limited slip that uses a cone to prevent excess slippage.

SelecTrac is what Jeep labeled the vehicles with NP228 and NP229 transfer cases (probably others in the other models?) which shift gears by way of a vacuum switch under the dash. These systems can operate in 2wd mode or full-time 4wd mode (i.e: drive on dry pavement in 4wd). The NP228 (1986) has no limited slip; the NP229 uses a limited slip similar to the NP219.

You may also have heard of CommandTrac and QuadraTrac II, the former being associated in my own pea brain with baby Wagoneers and Cherokees and is a shift-on-the-fly part-time setup operated by a single lever (anyone know what tcase?) The QuadraTrac II is the cool tcase optional in the brand new Grand Cherokees — the vehicles some of us will be driving afford in 10-15 years when they become affordable and our FSJs are rotting down to the frame.

The only relation "SelecTrac" has to differential operation is this — at some point in the early 1980's (83? 82?) Jeep started using a vacuum actuated axle disconnect in the D44 front axles, along with SelecTrac in the form of the NP229. You couldn't shift on the fly; you had to wait for the front axle to engage or disengage which coincided with selecting 2wd or 4wd. I'm not sure on the details of which models have this vacuum front diff. I am pretty sure this went away in 1984 and certainly by 1985.