Explain 4x4

[NS-jeeper]

Can some one explain what part time 4x4 is and what fulltime 4x4 is and what the difference is, my Cherokee has a light that says "part time" when you engage the 4x4, and how this compares to  say an old CJ7's 4x4.

[fug]

In fulltime 4x4 power is transmitted equally to the front and rear wheels, while in part-time there's some kind of mechanism that allows some slippage between the front and rear wheels.  The slippage in the part time makes it suitable for use on-road as the front & rear wheels aren't linked together allowing the vehicle to turn corners etc.  Full time 4x4 can't really be used on-road as there's no slippage between the front and rear wheels so you get "drive line bind"... which breaks stuff in hurry. (If you've ever tried turning on a hard surface with fulltime 4x4 engage you'd feel the front end hopping and lurching... thats driveline bind and it's really hard on parts).

Fug

[FeatherFoot]

In fulltime 4x4 power is transmitted equally to the front and rear wheels, while in part-time

You've got the correct answer, except that that from my recolection Jeep phrases the wording from a drivers point of view.  Part time by their definition means you only can drive it  some of the time (part time) in that position because the front and rear diffs are locked together.

Full time means you could drive the vehicle all the time (full time) if you wished, because the transfer case uses a center differential to split torque equally from front to back.

Full time is good for highway ice and snow because it drives very much like a rear wheel drive and all wheels can find their own speed on corners or if you back off the accelerator in a skid. Part time on ice is sketchy in corners and can get pretty dicey if you should get out of control on the highway.

The negative of full time is that the centre diff limits the torque to that of the wheel with the least traction, so if one wheel is off the ground, you have no torque to any of the wheels.

In my view (select trac) has been one of Jeep's best kept secrets.  There is no automatic clutching etc, just good ol predictable mechanics, yet by moving the lever to part time you have the same operation as a conventional (command trac) Jeep.  A good daily driver set up.

I don't know if it was always true, but when I bought new, select trac was only available with an auto tran.

[NS-jeeper]

my transfer case is a np231 command trac part time only. but which system is better for offroading..... I miss my dana 300!

[FeatherFoot]

Generally speaking for off-road, the more locked up the better, starting with the transfer case.  Select trac offers that functionality, but generally you're in two wheel to the trail and then locked up as much as possible. Command trac offers exactly that.  The necessary functionality with fewer parts to break.

[BlackYJ]

The cherokees with the full-time option also have a part-time option.  Part-time is the way to go.  Like featherfoot has already said the fulltime option just allows you to use 4wd on any road conditions with out fear of damaging the driveline because everything is locked up.

[cLAY]

my transfer case is a np231 command trac part time only. but which system is better for offroading..... I miss my dana 300!

The 4wd system on the NP231 is the same as a D300. When in 4WD front and rear axles are locked together and power is transmitted equally.

The NP242 t-case offered only on Cherokees equipped with the Select-Trac 4WD system offers an EXTRA 4wd position called fulltime 4WD.  It would have been better named All Wheel Drive as you can drive in this positon all of the time. There is no binding when doing tight parking lot manouvers like in reguallar 4WD.

The NP242 and NP231 are equally good for off-roading but there are more aftermarket parts available for the NP231.

[NS-jeeper]

Thanks guys this was all very informative.

[Wif]

my transfer case is a np231 command trac part time only. but which system is better for offroading..... I miss my dana 300!

The 4wd system on the NP231 is the same as a D300. When in 4WD front and rear axles are locked together and power is transmitted equally.

The NP242 t-case offered only on Cherokees equipped with the Select-Trac 4WD system offers an EXTRA 4wd position called fulltime 4WD.  It would have been better named All Wheel Drive as you can drive in this positon all of the time. There is no binding when doing tight parking lot manouvers like in reguallar 4WD.

The NP242 and NP231 are equally good for off-roading but there are more aftermarket parts available for the NP231.

As does my Durango. It has AWD (full time 4x4) and 4WD (part time 4x4) .. selected electronically on the dash. I also have a LSD in the rear.
You cannot select 2WD as per the YJ/TJ.
AWD delivers equal power to all 4 wheels under normal (stress normal) driving. This allows for predictable driving even in the rain as long as you drive normally.
But, if you're standing still and you hit the loud pedal hard, the rear will break away as if you're in 2WD .. and continue to do so as long as you apply power .. let off the gas (as long as the vehicle is moving) and allow the power to be distributed equally again and it will drive as a AWD (4x4). I find this a little unpredictable at slow speeds on snow. I can actually have the front wheels on dry grippy ground and have the rears spinning on ice and it will sit there doing it.
4WD locks the rear and fronts up .. and you can really feel it bind on corners if the surface under you isn't slippery.