So I have read and heard that the new JK has shift-on-the-fly into 4HI at speeds up to 55mph. But, I still have never once done this. My previous Jeep's (CJ, and Comanche love that truck) did not have this feature. I have had her offroad quite a bit, but I still stop every time I put it in 4wheel. I am pretty sure its quite a sophisticated system that is bulletproof, and I know I don't have to drive in reverse after 4wheel anymore, but I like to be extra sure that I can come out of my old-school tendencies. So...
1. Any problems/tricks I need to know about?
2. Can you shift into as well as out of 4-wheel? (I would think so)
3. How smooth is it?

 

Although I have never shifted into or out of 4hi at 55 mph, I have used it at much slower speeds like 5 or 10 mph. It shifts very smoothly both into and out of 4hi.

 

1. Nope
2. Yes
3. Very smooth

i just take my foot off the gas for a second when shifting.

 

Just let off the gas a little and put it in 4hi or back to 2hi. This isn't new to JK's, our old TJ had this same system. I pop mine back and forth a lot during the winter.

 

I have just purchased my first jeep. It is an 09 rubicon (4 door), automatic. Yes it does let you shift into 4 wheel drive while driving.

It shifts into and out of 4 wheel hi smoothly. Being new to 4x4 I thought they all did that. Truthfully it is as seamless as shifting from drive to one of the lower gears like 2

I have noticed it difficult to shift to 4 low. I believe the book says with the vehicle rolling forward slowly and in neutral, make the shift. I switched this procedure a little and now do the following.

I stop the vehicle, and with he transmission in neutral, make the shift. But sometimes the gears do not line up, and I will have to put it in drive and roll forward or backwards a few inches, and back to neutral to get it to shift in.

 

I have never shifted into and out of 4hi at 55 but I have done it fairly close to that. Like others said, just let off the gas pull the lever and you are good to go. It should be nice and smooth.

 

The only reason the CJ would not be able to shift on the fly is if the front wheels were locked out. You would have to stop, lock in the hubs, then proceed to shift into and out of 4wd on the fly.

The Comanche was also shift on the fly. The early models had a syncro in the transfer case to get the front drive shaft spinning, then a vacuum actuator would lock in the right axle, then as you continued to pull the lever, it would go into 4wd. The later models dropped the front axle disconnect. Since that made the front axle/drive shaft spin all the time the Jeep was moving, it remained shift on the fly.

Shift on the fly is not a "feature". It's the result of the manufacturers eliminating lock-out front hubs. The front axle's speed matches the rear, so there is no reason not to shift on the fly.

 

I go in and out of 4 wheel drive at around 55ish all the time, or at least I did when I lived where it snowed. No problems.

Just don't try shifting while your back wheels are spinning and your fronts are not. Could be tempting to do this when you are losing traction in the snow and don't want to stop.

 

i have shifted into 4hi at speeds of 45-50 mph if a standerd push in clutch then shift into 4wd . this should be very smooth, do the oppisite when shifting into 2wd

 

Have shifted hundreds of times in my KJ in and out of 4 hi and/or 4 lo. Just make sure to be
rolling a bit, 2 or 3 mph. Very smooth. Only problem is the time it takes to get into rear locker
mode, can take up to 5 minutes, but finally will. Then for the rest of the day in goes in and out
of locker mode within seconds. Don't know why, but it does work.