YJ vs. TJ 4WD question

[JasonS]

I know (or at least I think) That a YJ engages 4WD via vacuum. But how does a TJ engage/disengage.

It seems to me that the front driveshaft on a TJ would be turning all the time. but how does the 'hubs' lock and unlock if this is the case?

[Chris S]

Their are no hubs on either rig. YJs have a 2 piece axle shaft on the passenger side that is locked together by a vacuume operated shift fork. No vacuume+ open dif= no front wheels driving. If you have a front locker and lose vacuume you still have the driver's tire powered.

On TJs Chrysler got rid of the axle disconnect. The front axle is turning all the time.

[JasonS]

On TJs Chrysler got rid of the axle disconnect. The front axle is turning all the time. [/B][/QUOTE]

That's what i had thought, but what is the 'thud' you hear when you go back to 2WD while still driving?
ie: 'Shift on the Fly'

[Chris S]

The thud is the front driveshaft disconnecting inside the t-case. It should be very quiet, but if there is binding on the drive train (like if you have been driving on paved roads, or just turned sharp on hard pack dirt) then it can be hard to disengage. Under these conditions it can take a few seconds (or even a couple of minutes) until the t-case will release the front shaft.
I always make sure I am driving on a soft surface just before I disengage 4wd. If I hit dry pavement before I shift out of 4wd then I drive slowly with 2 tires on the shoulder while I shift the t-case in order to release any binding.

[Lauti]

I always completely stop when engaging and disengaging 4LO, although my owners manual says the vehicle can roll at 2-3kph. But I experienced once or twice some major grinding when doing that.

If shifting directly from 4LO to 2HI, I usually drive my TJ in the opposite direction for a few meters in 2HI, than just before in 4LO. Then usually hear the click in the t-case and know that I am in 2WD again.

If I was just in 4HI on a gravel road or on a snow covered road, then I shift on the fly. I also press the clutch during that process, or after the process for just a few seconds. While the TJ is rolling along the road, I wait for the click again, then it goes on without a worry.

[Chris S]

Right, I forgot to mention that you should always be off the gas when shifting the t-case.

[JasonS]

Thanks Chris S. Makes sense to me. I appreciate your knowledge. Guess it takes some getting used to I remember the old days getting out and locking / unlocking the hubs.

[sparky]

In the good Old, Old days the MB's were like TJ's, permantly locked in.

So don't feel bad, the TJ isn't designed for new lazy SUV owners, it's just based on 1940's technology.

[Colo.TJ]

When shifting on the fly try letting off the gas and reappling the gas a couple of times to get the drive shaft to disconnect.