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Unread 02-05-2009, 08:42 AM   #1
89SAFARIXJ
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NP242 Transfer Case: Full Time and Part Time, What's The Difference?

What is the difference between the full time 4x4 setting and the part time 4x4 setting on the 242 transfer case? what exactly is happening to make it "full" or "part" time?

-Sean

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Unread 02-05-2009, 08:48 AM   #2
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I believe that in "Part" time, your front and rear driveshafts are mechanically "locked" (i.e. they will always spin at the same rate... period), where as in "Full" time, they are allowed to rotate at slightly different rates (something synonymous with a limited slip differential). The "Full" time setting allows you to run in 4WD while on pavement and won't grenade your drivetrain as you make turns.
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Unread 02-05-2009, 08:48 AM   #3
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In the full time setting it lets the front and rear driveshafts spin at different speeds, kinda like a limited slip differential. This allows you to turn without binding, from the wheels traveling at different speeds. In the part time setting the front and rear shafts are locked so that there is no sliping. which will cause binding when turning. unless you are on a slippery surface. So fulltime can be used all the time on any surface, but parttime is to be used only when on snow/ice or dirt/mud, and so on. TheNerd beat me by a second or two.
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Unread 02-05-2009, 08:54 AM   #4
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Full time means you can use it any time, or all the time beucause the transfer case allows the front and rear axles to turn at different rates (like a differential in an axle does from side to side).

Part time locks the front and rear axles together at the transfer case so they are turning at the same rate all the time. This means you cannot use it on pavement because the axles will move at different rates, for instance, when you turn to go around a corner. The front axle takes a longer path than the rear and in turn has to move slightly faster. This works off road because there is enough of a lack of traction so wheels can spin at the rate they need to without binding up the transfer case.

Edit: I'm too slow...
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Unread 02-05-2009, 08:58 AM   #5
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Just to remove any confusion here as one reply mentioned viscous coupling and another reply mentioned limited slip. The 242 case contains an open diff that allows the front and rear driveshafts to rotate at different speeds in full-time, There is no viscous or limited slip! Selecting part-time effectively locks that diff, just like a mechanical axle locking diff.

In full-time if you chocked 3 wheels and jacked the remaining wheel off the ground then tried to drive away you wouldn't go anywhere but would simply spin the raised wheel.
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Unread 02-05-2009, 09:04 AM   #6
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Quote:
Originally Posted by sprintagogo View Post
The 242 case contains an open diff that allows the front and rear driveshafts to rotate at different speeds in full-time.
I did not know that. Good info!
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Unread 02-05-2009, 09:06 AM   #7
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okay thanks guys. just wondering how it worked "tehcnically".

-Sean
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Unread 02-05-2009, 07:23 PM   #8
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Originally Posted by sprintagogo View Post

In full-time if you chocked 3 wheels and jacked the remaining wheel off the ground then tried to drive away you wouldn't go anywhere but would simply spin the raised wheel.
tried to drive up onto ramps in FT, just slid ramps,had to use PT to pull front wheels up, FT works great on mixed pavement,much more stable
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Unread 02-05-2011, 01:54 PM   #9
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so then in part-time its just like a locker? all the wheels spin the same distance regardless of the torque they are putting out? why not just use full time all the time then unless your stuck?
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Unread 02-05-2011, 02:23 PM   #10
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so then in part-time its just like a locker? all the wheels spin the same distance regardless of the torque they are putting out? why not just use full time all the time then unless your stuck?
Well.. no, unless you have lockers in the axles as well. But one front and one rear tire will spin the same speed when in 4hi or 4lo.

You can use 4ft all the time, there's nothing to prevent from doing so. It can be used well over legal speed limits so no problem there either. But you get slightly better mileage in 2wd, and also won't have the front pulling so tires, u-joints etc. won't wear out as quickly.

I preferred using 2wd when during summer or if it was a warm in the winter (wet roads), but if it was below freezing, snowy or slippery I usually kept my XJ in 4ft. In deep snow I always used 4hi or 4lo. I really wont to swap the 249 on my Grand to a 242, I want the ability to run 2wd and locked 4hi.
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Unread 02-05-2011, 02:47 PM   #11
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but if 4x4 part time locks the wheels so they all spin the same then its just like a locker. where as 4x4 full time allows the front wheels to spin faster then the rear. and if i had a 249 and switch with a 242 and put it into 2wd will the front tires still spin?
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Unread 02-05-2011, 02:53 PM   #12
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Originally Posted by Darman View Post
but if 4x4 part time locks the wheels so they all spin the same then its just like a locker. where as 4x4 full time allows the front wheels to spin faster then the rear. and if i had a 249 and switch with a 242 and put it into 2wd will the front tires still spin?
Technically correct.

The 249 is 4wd all the time with a viscus coupler to act like a limited slip.

I do not believe it is ever "locked" even in low.

A 242 in 2wd will still have the front tires axle and driveshaft spinning, but it will be disconnected inside the transfercase and will not be "pulling"
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Unread 02-05-2011, 03:10 PM   #13
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Originally Posted by Darman View Post
but if 4x4 part time locks the wheels so they all spin the same then its just like a locker. where as 4x4 full time allows the front wheels to spin faster then the rear. and if i had a 249 and switch with a 242 and put it into 2wd will the front tires still spin?
Yes, and no to the first one. If you have the front and rear driveshafts spinning the same speed and locked together, but have open diffs in teh axles, you won't have all four wheels spinning the same speed. Think about a situation when you have one front and one rear wheel in the air, and two on the ground - the ones in the air will spin and you're not moving anywhere because of the open diffs. But yes, front and rear axles are locked together.

If you put a 242 or 231 in 2wd, it's in rear wheel drive so of course the fronts won't be pulling.


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Technically correct.

The 249 is 4wd all the time with a viscus coupler to act like a limited slip.

I do not believe it is ever "locked" even in low.
Depends on the age, later model 249s have a tru lock (like 231 or 242) in 4lo. The older ones rely on the viscous coupling in 4lo also, which make it suck big time when wheeling.
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Unread 02-05-2011, 03:51 PM   #14
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so in part time 4x4 it locks the drive shafts together so they spin at the same speed however that doesnt get transferred to the tires because of the open diff? allowing the tires to spin at different speeds even tho the front and rear shafts are locked together? where as in 4x4 full time the front and rear drive shafts spin at different speeds?
So with my jeep, 95 zj 5.2L v8 orvis edition quadratrac 249 tc, my front wheels are "locked" to the axle so even if i had a 242 tc in it and put it in 2wheel drive the front wheels would still spin the axle it just wouldnt be connected to the transfer case? so i could lift the front end and spin the tire by hand?
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Unread 02-05-2011, 03:52 PM   #15
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In Part Time and assuming open differentials, one front shaft (l or R) will be locked with one rear shaft (l or r). The differentials still do their part in allowing the shafts to move independently, let and right, but the full-time TC locks one front shaft to one rear shaft.
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