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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
I have read different things about this online, and I'm still confused. What is the difference between part time and full time on a 242? I know you can drive a 242 in 4WD full time all the time, unlike the 231. If you don't have a rear driveshaft installed and you put it in full time you won't move, and could damage something, but I don't know why.
Part time with a 242 is the same as part time with a 231. Slick conditions only. Deep snow, for example. Do not use it on dry pavement. Full time with a 242 is just that. You can use it all year round no matter what. As for driving around without the rear driveshaft in full time, i do not know. Never tried.
That didn't answer my question. I know what the different modes are used for, I want to know how they are different in operation. What does full time do that part time doesn't to allow use full time on the road? I know that you can't drive in full time without a rear driveshaft, because I tried before I installed the new transfer case output shaft and shims.
To answer your question simply put the part time case mechanically connects the front and rear axles with no slippage between the two, as for the full time case there is a set of clutches connecting the front and rear axles allowing for slippage needed between the two needed to run down dry pavement. If you pull rear driveshaft on a full time case it will burn up those clutches causing damage. Think of a full time case a a limited slip differential they are very similar in how they work.
To answer your question simply put the part time case mechanically connects the front and rear axles with no slippage between the two, as for the full time case there is a set of clutches connecting the front and rear axles allowing for slippage needed between the two needed to run down dry pavement. If you pull rear driveshaft on a full time case it will burn up those clutches causing damage. Think of a full time case a a limited slip differential they are very similar in how they work.
Actually it's planetary gears, not clutches, but the operation is similar.
To answer your question simply put the part time case mechanically connects the front and rear axles with no slippage between the two, as for the full time case there is a set of clutches connecting the front and rear axles allowing for slippage needed between the two needed to run down dry pavement. If you pull rear driveshaft on a full time case it will burn up those clutches causing damage. Think of a full time case a a limited slip differential they are very similar in how they work.
The NP242 dont have any clutches.. it has a set of planetary gears that act like an open diff when set to fulltime..
NP242 planetary gears
When in part Time the front and rear axle are locked together 50% front 50% rear.
In full time the np242 engages the planetary gears and splits the torque 48% front, 52% rear.. The planetary gears kinda act like an open diff in the T-case..
I would expect that functionality-wise since full-time 4WD is an open diff, if one tire loses traction the Jeep will sit there and spin that one tire. AMC Eagles used a similar setup in 1986 only with as I recall the NP128 transfer case. (Other years used a viscous coupling.) I had an '86 Eagle years ago and found that as a practical matter that kind of slippage rarely happened. With the 242 you of course would be able to switch into part-time 4WD, which the Eagle lacked.
..... If you don't have a rear driveshaft installed and you put it in full time you won't move, and could damage something, but I don't know why.
Why would you not have a rear drive shaft?
The way i understand and i could be wrong, if you don't have a rear drive shaft installed, the entire 4W full time system acts as an open diff. between the front and rear axles. All the torque goes to the least resistance, in this case the rear Tcase output (minus the rear diff. of course).
Similar as with an open rear diff., all the torque goes to the spinning wheel.
I would expect that functionality-wise since full-time 4WD is an open diff, if one tire loses traction the Jeep will sit there and spin that one tire. AMC Eagles used a similar setup in 1986 only with as I recall the NP128 transfer case. (Other years used a viscous coupling.) I had an '86 Eagle years ago and found that as a practical matter that kind of slippage rarely happened. With the 242 you of course would be able to switch into part-time 4WD, which the Eagle lacked.
The way i understand and i could be wrong, if you don't have a rear drive shaft installed, the entire 4W full time system acts as an open diff. between the front and rear axles. All the torque goes to the least resistance, in this case the rear Tcase output (minus the rear diff. of course).
Similar as with an open rear diff., all the torque goes to the spinning wheel.
I figured that out when I realized I was in part time on the road and thought I was doing something wrong, so I tried to shift on the fly to full time and go, but the only thing that sped up was the speedometer. I didn't have a rear driveshaft installed temporarily a while back because the transfer case output shaft was bent and the pinion angles were off causing bad vibrations.
The NP242 dont have any clutches.. it has a set of planetary gears that act like an open diff when set to fulltime..
NP242 planetary gears
When in part Time the front and rear axle are locked together 50% front 50% rear.
In full time the np242 engages the planetary gears and splits the torque 48% front, 52% rear.. The planetary gears kinda act like an open diff in the T-case..which allows the axles to go different speeds around corners without binding up and bucking.
How would your wheels be "locked" in part time if you have open differentials front and rear? Why 48% front 52% rear in full time, are they arbitrary numbers?
Last edited by chilipepper; 01-09-2017 at 05:02 AM.
How would your wheels be "locked" in part time if you have open differentials front and rear? Why 48% front 52% rear in full time, are they arbitrary numbers?
they're locked at the transfer case, not the differential. so if you turn on pavement in part time, the front axle and rear axle's wheels won't turn at the same speed, causing binding at the TC. full time allows slippage in the TC so you can use it whenever you feel like.
and why are the numbers so important? just put in your head the power is split at the transfer case 50-50 and stop thinking about it.
transfer case output shaft speeds are the same in Parttime. In Fulltime, there is a differential in the case to allow the output speeds to vary as needed.
transfer case output shaft speeds are the same in Parttime. In Fulltime, there is a differential in the case to allow the output speeds to vary as needed.
To think of it another way, FT 4WD is basically like AWD, at least how it would appear to the driver. The center diff does all the work of keeping things turning at different speeds on different surfaces. PT 4WD is just regular old-school 4WD where the two driveshafts are locked together. You can think of this as similar to having a locking center diff, though it's actually a transfer case.
By the way, what happened to the little clickable dropdown in each person's avatar showing the year, engine, trans, etc. of their XJ? That was very handy, but I've not seen it for a few weeks.
By the way, what happened to the little clickable dropdown in each person's avatar showing the year, engine, trans, etc. of their XJ? That was very handy, but I've not seen it for a few weeks.
01-07-2017, 09:06 PM
242 Transfer Case Modes
