part time 4wd=locked diffs?

[lussenden]

so i was looking around this forum and i read that part time 4wd, as opposed to full time, on my 1990 cherokee means that the front and rear are locked. is that really true? i do know that when it is in part time and i try to turn sharp on asphalt, the front wheels hop. so does part time 4wd= locked diffs?

[lussenden]

nvm. i misread it. it says it locks the front and rear wheels together. so what is the real diference between part time and full time 4wd?

[fredjacksonsan]

In a part time system, the center differential in the transfer case is locked when in 4wd, turning the front and rear at the same speed. You should never drive on dry pavement with your part time system in 4wd! Eventually you WILL break something on the Jeep, necessitating an expensive repair.

In a full time system (and all wheel drive type vehicles) the center differential in the transfer case is not locked, and allows the front and rear to turn at different speeds.


Think of your vehicle in a very sharp left turn. The RF tire moves MUCH further than the LR tire.

[lussenden]

so which one is better for off-roading? i normally used full time 4wd.

[fredjacksonsan]

Full time is fine if you're doing some mild things, but for maximum traction you'll want part time. Imagine spinning your wheels in mud....if there's a differential in the middle that's open, you could end up just spinning the front or the rear. With the middle locked together(part time) then you will be spinning both the front and the rear.

[AlohaBra]

Are you talking about the Command Trac vs. the Selec Trac?

The Selec Trac is the full time 4 WD and can be run in 4WD all the time (at a cost of less gas mileage) because of a diff unit in it so the transfer case will not get jammed.

Some of the newer full times and all wheel drives, not the XJ, use electronic locking of the center diff for off the road and heavy snow conditions. The Selec Trac does not do that.

Just wondering, isn't the low range in the Selec Trac fully locked? (I haven't had the full time in about 10 years.)

[lussenden]

i forget if mine is command trac or selec trac. but i have the NP242 transfer case which has the option of full time, part time, and low range 4wd.

[AlohaBra]

OK, the NP242 is a Selec Trac. I use to have one of these also. The ranges with the Low lever down is 4wd full time or 2wd. With the low lever up it is in 4WD low and the transfer case is locked and considered part time, so off-the-road this is the range to use in the rough stuff. Otherwise 4WD full time (or high range) is used anywhere else including fire trails or anywhere where you don't need low. I used two wheel drive on highways to save gas and wear and tear on the front tires.
To answer your first question, don't use the 4wd low or Part time on pavement because the front and rear are locked.