Driveline clunk

Hi, folks. This is my first post, been lurking for a while. I've searched every driveline clunk thread I can find but haven't found an answer to a problem I'm having, so here goes.

I have a 90 XJ, 4.0L, AW4, NP242. Has 223,000 miles on it, I bought it a little over a year ago with 189,000 miles on it. Currently has BFG AT's, 215/75R15 on factory alloy wheels. Basically stock, but about 6 months ago I swapped in Grand Cherokee V8 front coils, and added two additional stock leafs to my slightly sagging original leaf packs. I cut the eyelets off the main leaf of the donor pack, and added that plus the second leaf to my original packs. Front wheel center to bottom of fender flare now 19.25", rear is 18.25 inches, so about a 1.5" lift. Had no problems after this lift, no noises or driveline vibrations.

About two or three months ago, during normal acceleration at about 25 or 30mph, I heard/felt a loud clunk, seems like from the rear driveshaft area. It sounded/felt like what I would expect if something like a ujoint bound up and then suddenly let go. It doesn't make the noise all the time, and I haven't been able to pinpoint it with any specific event, shift point, etc. It never makes the noise at freeway speeds, only normal, surface street driving around 25-35mph. Always happens driving straight, light normal acceleration. If I let off the accelerator, it stops, but will often but not always clunk again as soon as I press the gas. Again, not hard acceleration, but just normal driving. I've even tried to be as easy as possible on acceleration, and it still clunks sometimes. I've tried it in both 2WD and full-time 4WD, and it clunks in both modes.

My first thought was ujoints, so I dropped the rear shaft and could feel no play in either joint. I pulled the two accessible caps off the rear joint and could see no problems there. Reinstalled the drive shaft without replacing ujoints and clunk was still there.

As it happened rather infrequently I lived with it for a while since I didn't have time to work on it, even made a trip from CA to Wyoming with it. In the last month or so the clunk has been more frequent, and now sometimes does multiple clunks in succession, same speeds as before, same conditions. They are loud, banging clunks.

I've had a wrecking yard Dana 44 waiting to be installed, so last week I decided to swap that in. After install, still the same clunking. Old rear axle was Dana 35, open diff, 3.54:1. Replacement Dana 44 is 3:54:1, factory limited slip. I did not go through the 44 except a fluid change, but I got the same clunk with either axle, so don't think it's in the axle.

I then checked the posts here again, and checked my motor mounts. Saw cracking on both mounts, so replaced them and the trans mount. The left hand motor mount was in two pieces, the right hand had just started to crack. The trans mount was quite squished compared to the new one, at least an inch shorter than the replacement. Thought this was for sure the cause of my problem. Replaced all three mounts, clunk still there.

Today I replaced the ujoints on the rear shaft. I inspected the old joints after removal, still could not see anything wrong with them, but put the new ones in anyway. Clunk is still there.

I've checked the torque on the rear spring ubolts and they are tight. I have not yet replaced the rear shocks, but have inspected them rather closely, top stock bar pin mounts appear fine, not loose, bushing not loose, bolts tight.

Any ideas?

Sorry for the length of the post, but I wanted to get all the info out there.

Thanks in advance for your help.

Is this a stock driveshaft and does the clunk happen continously? Does it happen once when you come to a stop and once when taking off?

Yes, it is a stock driveshaft. No, the clunk does not happen continuously. It does not happen when coming to a stop at all and it does not happen when I take off, only on normal light acceleration when vehicle has reached about 25-35mph, in other words, not at initial startup, but after the car is rolling. And it doesn't do it every time I start off, either. For example, I just came back from a drive of about 15 miles, all stop and go on surface streets. It made the clunk noise on two or three separate occasions during that drive. Also, when it does clunk, it used to be one or two bangs. Now it seems to be getting more like 5 or six bangs in rapid succession, unless I back off the throttle, then it usually stops. Again, easy, normal acceleration and when the vehicle reaches about 25-35mph, it bangs. Not every time, probably about every ten startups.

When I last had the driveshaft out, I did move it around quite a bit with the front yoke in the transfer case and the rear ujoint unattached, to see what angles the front yoke/ujoint reached it's travel limit. I think the rear suspension would have to be pretty close to full droop when the front ujoint hits the yoke, so I don't think that's what's causing it during normal street driving. Since this is now a Dana 44 rear axle, and this is the original shaft from the original Dana 35, I also checked the front yoke bottoming. I understand the stock Dana 44 driveshaft is shorter than the Dana 35 shaft, but in my inspecting it looks like with my slight lift that's not a problem. Regardless, I had the same banging with the Dana 35 in it.

It sounds to me like you've pretty much done everything yet I don't remember any discussion of the transfer case. It sounds like you could have a loose and/or slipping chain that tweaks out when you accelerate, but when the torque is off it stops because it straightens out at non-torquing pull and stops "jumping" gear teeth (the operative being that the jumping of gear teeth could be the clunk). If your shaft is good, u-joints good, diff good, suspension components good, brakes not messed up, the only thing left in the driveline past the trans is the T/C.

The T/C being right under you as you drive can sound like it's coming from the rear end especially if it's affecting the pull of the driveline. Check it out. I could be wrong (as I've been wrong at least once) but it's woth checking out.

ParadiseXJ,

Thanks for the help. Your suggestion of the loose transfer case chain sounds logical, but if I understand the 242 transfer case internals, 2wd is straight through shaft drive. While I've had a fair amount of shop time I've never been inside a transfer case, just looked at the pictures. So let me go out on a limb here (possibly embarassing myself) and describe how I think the 242 works. In 2wd, there's straight shaft drive from the input shaft of the transfer case to the output shaft. There is no front axle disconnect in a 242 XJ, so the front axles are turning during 2wd just from the front wheels rolling. The front pinion is driving the front driveshaft, which is driving the chain assembly inside the transfer case, but the mainshaft in the transfer case is uncoupled in 2wd from the chain, so in 2wd the chain is just freewheeling, with no load on it. Not sure if I have that correct or not, and maybe not because what you describe sounds logical and the banging occurs in both 2wd and full-time 4wd. If the chain is freewheeling in 2wd I'd expect the banging to either not exist or be less magnitude than in 4wd. But I may be wrong on how the 242 works. Can you or anyone straighten me out on this?

I've heard a 231 do that in my jeep in 2wd and 4wd. The chain was so
loose I think it was just kinda wadding up under the front output gear and
binding when in 2wd. When in 4wd the chain was just jumping and binding.
This was on a 92 xj without the front axle disconect and a 231.
One of those tcases( I can't remember 241 or 242, maybe both) can
brake a snap ring allowing the output shaft to move in and out and make
that noise.

Well, here's the latest on my driveline clunk. I got under it and split the transfer case and replaced the chain. First thing I noticed inside was the plastic filter screen pickup at the end of the oil pump pickup tube was missing. Then I noticed all the very tiny pieces of black plastic. Looks like the chain rubbed through the rubber tube between the steel pickup tube and the plastic pickup filter, and the filter came loose and was ground into very small fragments by the chain. So I cleaned out all the debris, replaced the chain and the oil pump pickup filter. I drove it about 45 miles with no banging, where before it would have banged numerous times in that distance. The next day I drove it from LA to San Diego and back, about 225 miles, with no banging. Over this weekend it, however, I felt what appears to be the same or similar noise, but much less frequent and much less severe than before. So there is a marked improvement since the chain replacement, but something is still going on in the driveline, or else I have a different problem that might have been masked by the first one. The clunking I heard this weekend was on a freeway interchange under acceleration around 45-50mph when it clunked a couple of times. I also noticed at steady 60mph speed some slight rpm fluctuation or pulsing, almost as if the torque converter was unlocking and locking, but it only did it for a few minutes. I think the loud banging is handled but maybe I also have a trans problem. It's an AW4 with 223,000 miles on it, so maybe it's getting tired. Guess I'll seach the forum for trans issues.

Thanks to those who replied with suggestions.