Question on Command-Trac

I have a 88 Cherokee with AW4 and Command-Trac with a stock vacuum motor actuated front-disconect axle. I always stop to shift into 4WD and have never had any problems.

However, I have read that Command-Trac can be shifted "on-the-fly". If the car is in 2WD, the front driveshaft is not turning and the ring gear in the open differential is stationary. Since the driver-side wheel is splined to an axle and the axle is splined to the differential side gear ( inside the open-differential), and the side gear is meshed with one spider gear(pinion). This spider gear is also meshed with the side gear on the passenger-side. Since the ring gear is not moving, the two (2) spider gears and two(2) side gears(inside the differential ) rotate in opposite directions. Likewise, the passenger-side intermediate axle shaft (before the vacuum disconnect housing) is rotating backwards, while the passenger-side axle shaft from the passenger-side wheel is rotating forward. So if the car is moving forward and I attempt a shift "on-the-fly" the splined shift collar(in the axle shift motor housing) will attempt to couple two axle shafts rotating in opposite directions. This is not good! What am I missing here? Is there some type of vacuum delay that allows the ring gear to start rotating first to drive both side gears in the same forward rotational direction, before the shift collar attempts to couple the intermediate axle shaft with the passenger-side wheel axle shaft?

Best regards,

CJR

Quoting the 1990 xj owner's manual on Command-Trac: "To engage, shift the transfer case lever from 2H to 4H while the vehicle is moving at any legal speed."

here...read through this thread...maybe it will answer your question...

http://naxja.org/forum/showthread.php?t=950080&highlight=front+drive+shaft

You can safely shift into 4wd up to 55mph, anything higher is at your own risk.

joe_peters said:

Quoting the 1990 xj owner's manual on Command-Trac: "To engage, shift the transfer case lever from 2H to 4H while the vehicle is moving at any legal speed."

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So am i to believe from this that i can shift into 4wd on the fly with my 1991 laredo with an np231?

i have a 2000 4.0 4wd with the command trac with the np 231... and i shift into 4 high on the fly... but never done it at high speeds... now 4 low... i do it at a dead stop, t/c in neutral and gear box in neutral, then pull it into 4 low, if it wont slide in. i release the brake and let it roll just a little bit and it slides in no problem

awesome_xj said:

So am i to believe from this that i can shift into 4wd on the fly with my 1991 laredo with an np231?

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No. For 1991 and later models you can only shift from 2H to 4H while moving in reverse.:roflmao:

joe_peters said:

No. For 1991 and later models you can only shift from 2H to 4H while moving in reverse.:roflmao:

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:bs:...that aint really funny...

Some newbie is going to believe you...

joe_peters said:

No. For 1991 and later models you can only shift from 2H to 4H while moving in reverse.:roflmao:

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All jokes aside...it's the muffler bearings that allow it to shift on the fly. Also make sure your blinker fluid is full.

Shift at will from 2 to 4 hi on slippery conditions. I did it with my 98 w/231 this winter (so far) and has been a life saver. Yes best done at lower speed though like 55 or under.

McQue said:

:bs:...that aint really funny...

Some newbie is going to believe you...

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You might be right, and with my luck they would run over my foot when doing it--Karma.:hang:

awesome_xj said:

So am i to believe from this that i can shift into 4wd on the fly with my 1991 laredo with an np231?

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CORRECT!

If you shift on the fly, make sure the front and rear wheels are turning at the same speed. Shifting while the rear wheels are spinning and the fronts are stopped can ruin your whole day. Used to make good money from the owners of Exploders that did that in winter, but they usually just grenaded the hubs. Our XJs cad do internal damage. Never had to fix any so it must not be to big of a problem. I wouldn't take any chances though.

jamiemac said:

If you shift on the fly, make sure the front and rear wheels are turning at the same speed. Shifting while the rear wheels are spinning and the fronts are stopped can ruin your whole day. Used to make good money from the owners of Exploders that did that in winter, but they usually just grenaded the hubs. Our XJs cad do internal damage. Never had to fix any so it must not be to big of a problem. I wouldn't take any chances though.

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Yeah...It makes a cringing clunk...done it a few times but I haven't been left stranded yet.- Usually it's when I'm trying to make it somewhere in 2 wheel and suddenly realize that if I have to stop or let off the gas to lock in (and lose momentum) that I might not make it.

jeepman121 said:

Yeah...It makes a cringing clunk...done it a few times but I haven't been left stranded yet.- Usually it's when I'm trying to make it somewhere in 2 wheel and suddenly realize that if I have to stop or let off the gas to lock in (and lose momentum) that I might not make it.

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thats why you dont wait to use 4wd =D... i always stop on a hill if i know im not going to make it... or let off, pull up wait a second and get back on the throttle lol

I can't answer the why of shifting on the fly, but I can tell you that I have, on multiple occasions, shifted from 2hi into 4hi at speeds around 35 mph with no problems. I find that my np 231 actually shifts better if I am moving at a decent speed than it does at a stand-still. When shifting into 4Lo, I've found it is best to be rolling forward at 2-4 mph with the transmission in neutral and then make the shift into lo.