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how to engege 4x4?

M

mitsumotors

NAXJA Forum User
Location
Winnipeg
okay, I have a NP242 and the AW4 and was just wondering, on icy roads:
1 - can i engage/disengage part time(4hi) at highway speeds?
2 - can i engage/disengage full time at highway speeds?
3 - can i drive in part time while in overdrive?
4 - can i drive in full time while in overdrive?
also, what is the difference between part time and full time? if i'm allowed to use full time on any conditions and part time on only icy roads why would i ever use full time? i could just use 2wd on regular driving and if the roads are icy i could use part time.

thanks:roll:
 
Do you have the owners manual for your jeep? Find the material in there on the Selectrac

what is the difference between part time and full time?
Click to expand...

In 2WD only the rear driveshaft gets power, while the front driveshaft is turned by the axle. In "part-time" 4WD, both driveshafts get power, and they are locked together. In "full-time" 4WD, the transfer case uses an open differential to move power between the front and rear driveshaft as needed. Basically the "full-time" mode is an All-Wheel-Drive mode that you can use all of the time. Meanwhile the "part time" mode locks the shafts together, which causes binding on turns and other situations where one of the shafts wants to spin faster than the other, thus it can only be used some of the time (when you are on dirt or some other slippery surface) and cannot be used all of the time.
 
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1 - can i engage/disengage part time(4hi) at highway speeds?- Yes; the verbiage in the manual is 'any legal speed' personally i try to keep it under 60 when i do it.
2 - can i engage/disengage full time at highway speeds? - Yes, same as above

3 - can i drive in part time while in overdrive? Yes
4 - can i drive in full time while in overdrive? Yes

also, what is the difference between part time and full time?
Part time locks the front and rear drive shafts in sync and doesnt allow any slippage in the t-case; it is true '4 wheel drive'. You will notice your jeep bucking (which is the driveline binding )in turns if you engage it on the street when dry.

Full time allows for difference between the front and rear, re-distributing power front or rear (via the path of least resistance); it is more like 'all wheel drive'. It drives smoothly in any conditions on any surface. I used it in any on road conditions short of snow or ice. I found on one of my jeeps (stock) that full time got me an extra mpg or so in around town driving, but others have not had the same experience, and that was the only jeep i ever dd'ed long enough to experiment with so ymmv.
thanks:roll:[/QUOTE]
 
Experiment with it and see what you're most comfortable with.
For ice I prefer full time, for snow part time. But thats snow and ice in the southeast US your canuck winters may be different. :wow:
 
mitsumotors said:
so part time is better on icy/snowy highways? even if i'm driving at highway speeds?
Click to expand...
No. When you make any kind of turn at all the front and rear driveshafts will want to spin at different speeds. Since the transfer case is locked up they cannot do that, so the point of least resistance is the wheel/ground surface, IE the front or rear axle WILL rotate at different speed than it wants to, and the tires on that axle will break surface contact and spin freely. If you are driving down an icy highway and breaking surface contact what happens? The jeep goes out of control

You MUST be on slippery ground when using part-time 4wd so that the wheels CAN break surfact contact. That is not the same thing as WANTING to use 4wd on slippery ground...

Part-time 4WD above 30 MPH really only works on dirt/gravel roads but is not at all suitable for winter highway speeds
 
ehall said:
No. When you make any kind of turn at all the front and rear driveshafts will want to spin at different speeds. Since the transfer case is locked up they cannot do that, so the point of least resistance is the wheel/ground surface, IE the front or rear axle WILL rotate at different speed than it wants to, and the tires on that axle will break surface contact and spin freely. If you are driving down an icy highway and breaking surface contact what happens? The jeep goes out of control

You MUST be on slippery ground when using part-time 4wd so that the wheels CAN break surfact contact. That is not the same thing as WANTING to use 4wd on slippery ground...

Part-time 4WD above 30 MPH really only works on dirt/gravel roads but is not at all suitable for winter highway speeds
Click to expand...

Wow, I may have screwed up my transfer case then.

I've used it before on slushy highway roads.

And if you have the 231 it's not supposed to by engaged when turning? Only when going straight on super slippery stuff?
 
JoshRountree said:
Wow, I may have screwed up my transfer case then.

I've used it before on slushy highway roads.

And if you have the 231 it's not supposed to by engaged when turning? Only when going straight on super slippery stuff?
Click to expand...

No, I don't think that's what "e" meant at all.

He meant that with the 242, when you have the option of a "full-time," it performs better in snow than the "part-time."

But since part-time is all you (and most of us have), it'll do just fine.

And as long as there's a little "give" in the surface traction, you won't hurt a thing...

Robert
 
i might be wrong but use full time all year round rain, snow, ice, etc. and part time if you absolutly arent going to be on anything other than loose surfaces you could use part time on snow but why would you if you come to an intersection where you need to turn and its been cleared of snow and its just wet your going to get binding going round the turn and even if you say to yourself while your sitting still at the light im going around a turn better take it out of part time its not going to shift right out of p/t since your not moving and youll get binding hope this makes sense
 
I looked into a little bit and I'm not sure if I use part-time like it's supposed to be. Are you only supposed to use it on super slippery roads, and only in a straight line? I've gone around a curve in mine at a very low speed in 4hi part time and felt it jumping, am I not supposed to do this?
 
I'm not sure I quite understand how the front and rear wheels turn at different speeds. I know that the front axle outside wheel turns faster during a turn than the inside but it seems like they should balance out with the open diff. Seems like the front and rear axle should turn at the same speed, but the power split appropiatley by the diff.
 
yes your not supposed to do this if you hear binding your doing damage its the differance between front and rear wheel speeds not side to side axles are locked togeather in part time so they bind on other than slippery surfaces
 
JoshRountree said:
I'm not sure I quite understand how the front and rear wheels turn at different speeds. I know that the front axle outside wheel turns faster during a turn than the inside but it seems like they should balance out with the open diff. Seems like the front and rear axle should turn at the same speed, but the power split appropiatley by the diff.
Click to expand...

Same theory, different direction.

When you turn in an arc, each front wheel traces a larger circle than its trailing rear wheel. Since each front is travelling faster than the same-side rear, the front average has to be faster than the rear average.

Thus, the axles want to spin at different speeds.

Make sense?

Robert
 
Looks like my transfer case is where my driveline slop is the. Time for a rebuild. Sounds like you don't need to use 4wd unless you're going in a straight line and traction is crappy
 
WrenchMonkey said:
No, I don't think that's what "e" meant at all.

He meant that with the 242, when you have the option of a "full-time," it performs better in snow than the "part-time."

But since part-time is all you (and most of us have), it'll do just fine.

And as long as there's a little "give" in the surface traction, you won't hurt a thing...
Click to expand...
Let me clarify here

The only appropriate use of part-time 4WD (shafts locked together) is with LOOSE surface like dirt and gravel, and some kinds of snow. If you drive it on hard road the wheels will not be able to break surface contact very easily and you will likely damage something else (something has to give, whether it is driveshaft or differential or transfer case--hopefully it is the wheels!). Similarly if you drive it on slippery surface (rain, ice, some kinds of snow), the wheel under power on one of the axles will absolutely break surface contact, and if the road is slippery enough the wheel may not regain traction (the same principle as why you do not want to spin the wheels in rain or ice on a regular 2WD car).

A 242 has an open differential that allows the front and rear shafts to be powered independently. One wheel will always have traction and the others will just follow along without breaking surface contact. This can be used on dry, loose, or slippery surfaces as you please.

For a 231 on ice/rain highway, 2WD is the smart thing
 
When I pull the gear selector from 'N' to 'D' i get a very noticable buck. Could that be a stretched chain as a result of running it in 4wd part time when I shouldn't?
 
Think of it like bicycle gears. You can change at a stand still, but it won't fully engage unless you are moving. If it only partially engages it may bind up, or it may pop back out when you do start moving. You really need to be in motion for the shift to fully engage.
 
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