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Clunk/lurch into Drive, but not Reverse

Your transmission guy must not be a differential guy, 'cause that is where the clunk is coming from.
 
FOLLOW UP: Just got my XJ back from the transmission shop. It was in there for over 2 months, during which he completely rebuilt the transmission and the torque converter, replaced the valve body and the transmission control module and even the transmission case, and at the end he said that he and all of his fellow transmission shop owners on a network were all completely stumped as to why none of that fixed the problem. He did not charge me for any of this, because he said that he does not charge if he can't fix the problem. He was still pretty much 100% sure that the transmission would be the problem, but at that point he said the only thing that I could do would be to actually replace the entire transmission with a rebuilt one, and hope that doing that would solve the problem.


Wow, he did a lot of unnecessary work! Even replaced the TCM, he really thought it was an electronic issue? Can't fault him though, since he was incredibly honest and he didn't charge you for what would have been a very expensive bill at any other place even if they didn't fix the issue. The AW4 is pretty robust and probably didn't need a rebuild, btw
 
Have you actually been under the Jeep when someone is shifting to see where the noise is coming from? If it that loud and that noticeable, you will have no trouble ascertaining what is making the noise.

As far as the slip yoke "sliding down" due to gravity. It cannot happen! The rear driveshaft is a single piece with end one fastened to the axle differential pinion, the other end slides on the slip yoke at the transfer case. The only time the slip yoke "slides" is when the axle cycles up and down, changing the distance between the axle and the transfer case.

So, get under it and listen/feel and report back.
 
Have you actually been under the Jeep when someone is shifting to see where the noise is coming from? If it that loud and that noticeable, you will have no trouble ascertaining what is making the noise.

Mechanics have forever run vehicles in place, either held in place with blocks, up on jack stands or on a lift, so the problem or noise can be isolated.
Surprised this wasn't done at the transmission shop or, if they did, the location of the noise could not be determined.

Block all four wheels, front and back, and have a helper shift it back in forth, from Drive to Reverse, while you observe what is going on underneath, looking in from both the driver and passenger sides.
With bigger tires, I like 4X4 blocks.
 
OK... I took the XJ out to a wide boat ramp and tried every possible XJ orientation and ways to shift into Drive including in 4H and 4L, and the only thing that that will eliminate the violent clunk/lurch completely is if the XJ is traveling either in 2H or 4H at > 10 mph when shifted into Drive, or at > 5mph if in 4L.

I got under the XJ (again) while it was being shifted, and the ringy sounding "clunk" noise comes from the differential, and I noticed that the degrees of travel of the rear drive shaft when shifting into Drive is more than twice the travel as when it is being shifted into Reverse (all U-joints are tight, btw). So far I've been trusting that the veteran Master Jeep Mechanic (who has worked on hundreds of XJ's) and the veteran transmission guy (who rebuilt the transmission for free) knew what they were talking about when they said that it is the transmission that is the problem and not the differential, but now I'm starting to wonder if it might be the differential that is the problem.

The assumption up until now has been that the transmission is causing the violent engagement clunk/lurch, but maybe it is just that the forward direction function of the differential has SO MUCH PLAY in it that the drive shaft has enough free play to be able to build up speed before the play is taken up, and what I am experiencing is the HAMMERING of the gears against one another when the play runs out. (If you hit a bell with a hammer from 6" away, it will ring loudly, but if you hit it from 1/2" away, it won't).

If it IS the differential, I don't know why this Chrysler 8.25 would be in such bad shape after only 98K miles, with none off-road. My understanding is that if the previous owner operated the 231 transfer case in 4wd on dry pavement, it would never hurt the rear differential, because the rear differential doesn't even know whether the XJ is in 2wd or 4wd, correct?

Another theory I had about this problem was that maybe the transmission is starting out in a high gear instead of low gear when placed into Drive, but that theory got shot down when I affirmed that it only goes into 1st gear when it is put into Drive. Shifting directly from Neutral to 1st gear with the gear selector gets rid of the clunk NOISE (which I think is the differential "ring" gear actually "ringing", but the lurch is pretty much just as violent as when going from Neutral to Drive.
 
Your transmission guy must not be a differential guy, 'cause that is where the clunk is coming from.

I'm starting to think that you are correct (see my full post down below if you want details). Questions about Chrysler 8.25:

1. Should the rotational play of the drive shaft be about the same when shifting into Drive vs. into Reverse? Mine has more than twice as much play in the Neutral to Drive direction.

2. Ever heard of a Chrysler 8.25 failing like that with 98K miles, none off-road, on a very well cared-for XJ?
 
Just to add to the confusion (on my part, anyway), I just confirmed that despite the large difference in differential play when going into Drive vs. Reverse, if I MANUALLY rotate the drive shaft back and forth rotationally (U-Joints are tight, btw), the differential play is seems very minor to me:

With transmission and transfer case both in neutral, I'm measuring 4.5 degrees of play on the rear drive shaft (2.5 mm or .1", measured at outer surface of drive shaft).

(2.5mm play / 200mm circumstance) x 360 degrees = 4.5 degrees of play.
 
Since the differential spends 99.99 % of its life in forward drive, one might expect more wear on the forward motion side of the differential internals. The cause of any measurable excess wear is a good question. A teenaged male doing neutral drop burn outs would be a good suspect.

Chrysler Clunk is a commonly heard description of the symptoms. Have an experienced differential technician check/measure the ring and pinion backlash, the condition of the spider gears, the condition of and pre-load on the differential bearings, and the ring/pinion engagement pattern.
 
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98K doesn't seem like much - I'm still on the original 27-spline version of that with my '92 and it's got 256K miles on it with no issues.

Could whatever holds the pinion into the diff housing be loose (crush sleeve? yoke nut?), causing something that normally shouldn't rotate to have to spin a little before you start taking up the R&P mesh slack?

In other words, is the amount the rear driveshaft twists when you put it into Drive and it clunks equal to or greater than the amount you can twist it by hand? If putting it into drive gets more rotation, perhaps there really is something "else" rotating under the greater torque of the engine/trans that shouldn't be?
 
There are too many weird things going on here. I'm no master mechanic but I'm smart enough to know a clunk pretty much will never come out of an automatic transmission directly. I most certainly would not rebuild one,especially if I was a transmission expert. There are several things that could cause a clunk,most common is bad u-joints(most people grab the driveshaft,while the vehicle is on a slight incline,in park with tension on the drive train) and say feels tight,same with the rear gears or possibly even the t-case. I like to put them on fairly level ground, a tire chock both for and aft of a wheel of your choice. Put the transmission in neutral and grab the rear driveshaft and twist back and forth.
You should find it fairly quick.
Good luck
 
With transmission and transfer case both in neutral, I'm measuring 4.5 degrees of play on the rear drive shaft (2.5 mm or .1").

(2.5mm play / 200mm circumstance) x 360 degrees = 4.5 degrees of play.

I've had a friend switch between reverse and drive while I was under the rear end, and the only thing for certain is that it never clunks/lurches going into reverse and always clunks/lurches going into drive. It's AS IF the idle was at about 1500 RPM and then of course there would be a clunk/lurch, but the idle is only 740 RPM which seems to be normal for an XJ...AND, it NEVER does it in Reverse.

I'm going out right now to video the differential area so I can post exactly how violently it clunks/lurches when put into Drive.
 
That's a lot of play in the ring/pinion.
 
After watching your vids, defiantly in the diff. I know you did a static test to get your 4.5* but to me it looked like a little more than that. Combo of r & p plus side gears worn? You might have play in the thru shaft too. Found it interesting that it would back off a little bit when put into N and I don't think you can generate that much force by "hand" that you would be able to go up against it as it were and have it spring back a degree or two. Pull the cover and have a look, curious to know what you find!
 
Have a knowledgeable technician inspect the differential and spider gears, check the ring and pinion gear pattern, check the carrier bearings, and measure the pinion preload and backlash.
 
The 4.5 degrees (0.1") was by hand using a lever as hard as I could, with trans & tc both in Neutral. I can only guess that although the diff obviously has enormous play, that enormous play only occurs when an enormous (engine driven) jolt is applied.
I'll post a video of a hand/lever test today, so readers can see the huge contrast.

After watching your vids, defiantly in the diff. I know you did a static test to get your 4.5* but to me it looked like a little more than that. Combo of r & p plus side gears worn? You might have play in the thru shaft too. Found it interesting that it would back off a little bit when put into N and I don't think you can generate that much force by "hand" that you would be able to go up against it as it were and have it spring back a degree or two. Pull the cover and have a look, curious to know what you find!
 
After watching your vids, defiantly in the diff. I know you did a static test to get your 4.5* but to me it looked like a little more than that. Combo of r & p plus side gears worn? You might have play in the thru shaft too. Found it interesting that it would back off a little bit when put into N and I don't think you can generate that much force by "hand" that you would be able to go up against it as it were and have it spring back a degree or two. Pull the cover and have a look, curious to know what you find!
 
98K doesn't seem like much - I'm still on the original 27-spline version of that with my '92 and it's got 256K miles on it with no issues.

Could whatever holds the pinion into the diff housing be loose (crush sleeve? yoke nut?), causing something that normally shouldn't rotate to have to spin a little before you start taking up the R&P mesh slack?

In other words, is the amount the rear driveshaft twists when you put it into Drive and it clunks equal to or greater than the amount you can twist it by hand? If putting it into drive gets more rotation, perhaps there really is something "else" rotating under the greater torque of the engine/trans that shouldn't be?

At this point, my amateur guess would be that something is seriously loose in the differential, but, as you say, such that it is only really noticeable under engine force.

Videos:

'99 Jeep Cherokee XJ differential play (TC & Trans in Neutral). Much less visible play when doing manually - when not using engine power and sudden transmission engagement into Drive to jerk the drive shaft around:

https://www.youtube.com/watch?v=WRZI...ature=youtu.be

https://www.youtube.com/watch?v=yLV5XDG1J90&t=36s

https://www.youtube.com/watch?v=99t7lKHlUqw
 
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