4WD high thumps 1/4 mile after disengaging

96 4.0 XJ 4wd Sport 300K miles Part Time 4WD system

I didn't have any luck searching for a similar topic.

We got our first serious snow of the season today. I drive twenty miles one way to work and I got plenty of use out of the 4WD today.

The roads were covered this morning so I used 4-high the entire drive. When I went home only a few parts of the road were slick enough to use 4WD and since it is a Part Time system I wound up engaging and disengaging the 4WD three times on the trip home.

The first time I shifted from 4WD to 2WD I felt a "bump" and heard a "thump" after about a quarter mile of driving in 2WD. I thought I had hit a little pot hole. I was driving around 40mph. It happened to me two more times under the same circumstances and I realized I wasn't hitting pot holes.

I pulled into my driveway and used 4-high one more time and everything seemed to work properly. I don't feel anything or hear anything unusual when I engage the 4WD. When I got to my parking spot I put it back in 2WD and backed up about twenty feet then pulled forward again to see if I would feel or hear it disengage with the same "thump/bump" but I didn't.

Is it taking my 4WD a quarter mile to disengage and why does it feel like I hit a pot hole? I know this can't be normal. Has anyone else experienced this and should I be concerned?

What you describe is not normal, but not abnormal either. Drive line binding from different diameter tires or from worn axle shaft u-joints will cause that. Transfer cases that do not get used regularly or have worn shift fork tabs are sometime stubborn to shift back to 2wd. The 242 also does that very often as a side effect of the Full-Time mode.

Some people say that synthetic ATF makes the transfer case shift more smoothly.

Tim_MN said:

What you describe is not normal, but not abnormal either. Drive line binding from different diameter tires or from worn axle shaft u-joints will cause that. Transfer cases that do not get used regularly or have worn shift fork tabs are sometime stubborn to shift back to 2wd. The 242 also does that very often as a side effect of the Full-Time mode.

Some people say that synthetic ATF makes the transfer case shift more smoothly.

Click to expand...

I appreciate your reply.

My axle u-joints are fairly new. I had them replaced back in July with Precision brand when the XJ started "limping". My tires are all the same size except the rear set are newer than the front and studded. I only occasionally use the 4WD and when I do I don't leave it in very long.

I'll see if the synthetic ATF helps. So long as nothing snaps in the driveline I'll be happy.

Thanks again!

My best guess is that your shift linkage is probably worn out after 300k miles.

It is doing the job shifting to 4wd but I feel like it is only getting you 95% out of 4wd. It takes a lot of force sometime to get out of 4wd and with the oem linkage it may have a tiny bit of slack that isn't getting 4wd completely disengaged.

I believe the thump is the driveline finally kicking the tcase the rest of the way out of 4wd back into 2wd or it almost getting reengaged to 4wd.

I have an upgraded shift linkage in my off road XJ but an oem shifter in a stock XJ. The difference between the upgraded, more direct shifter is night and day. With the stock shifter I am always doubting if the shift actually engaged anything.

It is possible to lay underneath the jeep and inspect it. I believe that there is a way to adjust the stock shifting mechanism to get it back to a tight shift feeling.

Have Fun in the snow!

Disengagement of the mode fork in a 231 is spring actuated. When you move the lever from 4wd to 2wd, all you are moving is the linkage. Spring pressure returns the fork to 2wd. So, if there is any pressure on the driveline from an odd size tire or other source, it will stay in 4wd mode until it unwinds enough for the spring to return it to 2wd.

inspect the detent spring for the shift fork, fluid level, swap out tranny mount, replace u joints, and see if it continues.
Inspect motor mounts too.

If its still doing it, drop the tcase and see whats going on internally.

Thanks everyone.

I'm sure I have more worn parts than good parts. :explosion waiting to happen. It sure does run good though.

It probably doesn't help things that the torque converter is stuck unlocked. RPMs are always greater than they should be.

I wonder if it would help to shift the tranny to neutral before shifting from 4 high to 2WD. That would relieve any pressure on the driveline, right?

Forgive my ignorance. I envy those of you with mechanical knowledge.

Are you shifting it like this?

Here's how the factory suggests you shift the transfer case and I've been doing this since these things were new and I worked at the dealership. Quoted from the owner's manual. The suggestions in CAPS are mine.

"To engage, shift the transfer case lever from 2H to 4H while the vehicle is moving at any legal speed". I LET OFF THE GAS, THROW THE LEVER, TAP THE GAS AND LET OFF.

4L position: " To engage, slow the vehicle to 2-3 MPH , shift the transmission to Neutral, then shift the transfer lever to the right and pull firmly rearward to 4L".

TO SHIFT OUT OF 4L, SHIFT THE TRANSMISSION INTO NEUTRAL WITH THE VEHICLE STOPPED, SHIFT THE TRANSFER CASE LEVER TO 2H, THEN THE TRANS TO D IF YOU HAVE AN AUTOMATIC, OR INTO FIRST GEAR WITH A MANUAL, AND CONTINUE ON.

Revised 11/20/2014

cruiser54 said:

Are you shifting it like this?

Here's how the factory suggests you shift the transfer case and I've been doing this since these things were new and I worked at the dealership. Quoted from the owner's manual. The suggestions in CAPS are mine.

"To engage, shift the transfer case lever from 2H to 4H while the vehicle is moving at any legal speed". I LET OFF THE GAS, THROW THE LEVER, TAP THE GAS AND LET OFF.

4L position: " To engage, slow the vehicle to 2-3 MPH , shift the transmission to Neutral, then shift the transfer lever to the right and pull firmly rearward to 4L".

TO SHIFT OUT OF 4L, SHIFT THE TRANSMISSION INTO NEUTRAL WITH THE VEHICLE STOPPED, SHIFT THE TRANSFER CASE LEVER TO 2H, THEN THE TRANS TO D IF YOU HAVE AN AUTOMATIC, OR INTO FIRST GEAR WITH A MANUAL, AND CONTINUE ON.

Revised 11/20/2014

Click to expand...

2H - 4H I let off the gas but I don't tap the gas after shifting.

Any time I shift to 4L I put the tranny in neutral and come to a full stop before putting it in 4L. I can see how having a little forward movement would be beneficial but it isn't always practical. Living in the mountains there is minimal room to get off on the shoulder (if there is a shoulder). There are many, many miles of guardrail around here. Slowing down to 2-3 MPH on a snowy highway is a good way to get hit by some idiot coming over a hill or around a curve too fast. If I need 4L in the mud it's usually to get up or down a mud slicked rocky hill and with the lack of level ground here you aren't going to have the 'runway' to maintain 2-3 MPH while in neutral most of the time. Having a part time 4WD system complicates that even further because you have to wait until you are where the tires can already slip before engaging the 4WD. Try riding the brakes down a muddy or icy hill while maintaining 2-3 MPH with no anti-lock brakes to shift to 4L and it might just get away from you first.

What is your suggested method for shifting from 4H to 2H? That's the only time it hangs up - and only on the snow/ice covered highway. I have no issues with it off road. I normally let off the gas and just push the lever forward.

Same as 2 to 4 and AT SPEED.

The 242 is much more sensitive to shifting problems, by design, than the 231.

Check this out.

https://www.youtube.com/watch?v=u0Lk2r6OmDw