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On-The-Fly 4WD, Wrangler?

GrayT

GrayT

NAXJA Forum User
Location
CSprings
Alright, I've tried to tell my friend that his YJ has the same transfer case as mine, NP231, and that he can shift on the fly just like I can.

He is extremely reluctant to try it out while even rolling 1mph, he stops in the middle of traffic to turn his 4WD off when he leaves patches of ice on the road.

Can he do the same or am I just stupid? Does he HAVE to literally stop to shift into 2WD again?
 
When all else fails, read the intructions. LOL
Ditto on the owners manual. He'll soon see the he was wrong.
 
I had a 91 wrangler w/231 shift on the fly...IIRC the driver side sunvisor has a sticker on it that mentions something about this or maybe it was just the shift pattern or something...but then again that was 6 yrs ago.

I still have the manual if he wants it....
 
the owners manual states that you can shift from 2wd to 4HI on the fly at any legal speed (it doesn't directly say it, but was written with the intend of being 55mph or less). to shift into 4LO, you are supposed to be less than 3mph.
 
Cherokeelaredo said:
Do you need to put it in neutral to shift, or can you do it while in Drive.
Click to expand...

55mph or lower can be done from 2WD to 4HI

3mph or lower in NEUTRAL can be done from any gear to 4LO
 
your xfer case doesn't determine shift-on-the-fly status. all yj's come with a disco on the front axle. if you try to shift at 55 mph, you're going to have major grind. tj's came with non-disco axles anabling them to be shift-on-the-fly. be careful, your buddy has it right.
 
and you got it wrong...What year jeep do you have jeepdad?Do you have a jeep with the vac disco axle???Have you ever tried to shift one on the fly??I'm not being rude I'm just curious...
I've done it in my 89( np 231/vac disco) cherokee,a 91(np231/vac disco) wrangler,and another 86 cherokee with np 207 case.All three of which have syncronizers,just like a manual tranny,to allow shift on the fly.It doesn't matter if it's a vac disco or non....

although I haven't done it at free way speeds I have done it around 35-40 with no ill affect.The key is if it is a manual...shift into neutral and hold in the clutch while shifting into 4 wheel on the fly.I have no advice on how to shift on the fly with a auto,I've never owned one.

For christ sake,tell him to grow some balls and bang it into 4hi on the fly!!
 
Last edited:
jeepdeepfreak, i have a 94 yj, well maintained, and it does not like to be shifted into 4hi at any speed over 20. grinds like a mogator. i've replaced the shift motor and still have the same affect. doesn't sound like there's anything synchro'd going on there. it will come out of 4hi at any speed however without as much as a peep. you got me thinking now, maybe i have another issue. just my 2 cents.
 
there is no syncro on the disco collar, it's just a spline piece of steel tubing basically.
I've shifted my MJ on the fly into and out of 4Hi doing about 25. No issues.
87, 231, disco axle.
 
exactly. the splines get out of synch from each other due to wheel/axle rotation. the splines have to realign and mesh when the fork tries to push the collar over the outside axle. under 20mph seems to be ok, but any faster and that's when the grinding begins. to disconnect, the collar simply slides off the already aligned splines effortlessly. i'm not saying it can't be forced into submission, but it ain't pretty. just don't want to see anyone beat their s**t up needlessly.
 
Jeepdad, I wonder if your vacum pump that actuates the disco isnt losing pressure somewhere. All that disconnect does is start the front driveshaft turning so it will engage. There is no syncro in the t-case, it relies on the fact that the front and rear driveshafts are already turning at the smae speed, and then it just slides into gear. This is why if you are spinning tires it wont engage and just grind. Jeepdad, have you ever had the gears replaced in your Jeep? the reason they say you can shift at 55 or lower is that the gears in any 4wd vehicle arent exactly the same. There are usually 3.54 in the front of an XJ and 3.55 out back. Why? the 3.54's being ever so slightly taller pull the vehicle slightly faster than the rear. This keeps the front end straight. if you had something a little more different, like 4.27 and 4.30 then it might not be very happy shifting over 20 mph.

To answer the original question, if everything is working properly, he will be able to shift up to about 55mph without doing any damage whatsoever.
 
GrayT said:
Alright, I've tried to tell my friend that his YJ has the same transfer case as mine, NP231, and that he can shift on the fly just like I can.

He is extremely reluctant to try it out while even rolling 1mph, he stops in the middle of traffic to turn his 4WD off when he leaves patches of ice on the road.

Can he do the same or am I just stupid? Does he HAVE to literally stop to shift into 2WD again?
Click to expand...

Maybe your friend is confused. You can put it into 4WD just fine, but you either have to stop or be going really slow to put it into 4 low. Most my friends who have Wranglers stop to put it into 4 low, but I can put mine in when I'm going like 5 mph... So, maybe he is getting 4WD and 4 low confuzzled? lol
 
MIXJ:All that disconnect does is start the front driveshaft turning so it will engage.

huh? that's backwards. the energy goes the other way. the disco just connects the axle pieces together.

MIXJ:This is why if you are spinning tires it wont engage and just grind.

grind, that's what i'm saying. how does your jeep know the difference. don't the wheels "spin" when you're driving? the problem is that it is improbable if not impossible for the 2 axle pieces to rotate exactly the same. the collar has to grind until it happens to catch and align with the splines on the outside axle allowing it to engage. that's why it helps to be moving a little to encourage that to happen. moving too fast though and the process is hindered. this is only my opinion on what is happening to greyt's friend's yj. he is doing himself a favor to slow down when going into 4hi. coming out of 4wd is not an issue.

MIXJ:To answer the original question, if everything is working properly, he will be able to shift up to about 55mph without doing any damage whatsoever

famous last words. read 'em and weep.
 
Jeep01dad said:
MIXJ:All that disconnect does is start the front driveshaft turning so it will engage.

huh? that's backwards. the energy goes the other way. the disco just connects the axle pieces together.

MIXJ:This is why if you are spinning tires it wont engage and just grind.

grind, that's what i'm saying. how does your jeep know the difference. don't the wheels "spin" when you're driving? the problem is that it is improbable if not impossible for the 2 axle pieces to rotate exactly the same. the collar has to grind until it happens to catch and align with the splines on the outside axle allowing it to engage. that's why it helps to be moving a little to encourage that to happen. moving too fast though and the process is hindered. this is only my opinion on what is happening to greyt's friend's yj. he is doing himself a favor to slow down when going into 4hi. coming out of 4wd is not an issue.

MIXJ:To answer the original question, if everything is working properly, he will be able to shift up to about 55mph without doing any damage whatsoever

famous last words. read 'em and weep.
Click to expand...


Hmm, well he finally went ahead and tried it. First at 5mph, then 10mph, 25, 40, 55, then he stopped at that. All with no grinds.

Guess it just depends. Does the T-case not have synchros to help engage 4WD? Technically if it didn't it would grind going 1mph all depending on how fast you throw the shifter into 4HI.
 
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