NP242 noises and output shaft play?

My NP242 is making some odd noises and I'm wondering how concerned I should be about them. First, when I have spin the front driveshaft/front input shaft by hand with the case in 2wd I can easily hear what sounds to me like the chain moving inside the case. The noise seems normal enough, other than the fact that I can hear it so clearly. It sounds like a very big bicycle chain spinning. My alignment shop first pointed this out to me as something that may not be a normal noise, but they're not drivetrain guys so they weren't sure.

Secondly, when driving below 10 or 15 mph I hear a kind of "chuff-chuff-chuff" sound that seems to correlate to each turn of the driveshaft. I thought it was a front wheel bearing or u-joint going out until I noticed the sound had vanished when I had to move the Jeep with the rear driveshaft removed the other day. I just drove it around the block in 4-hi part time so I could pull it into my other driveway and the sound was gone.

Finally, I've recently noticed my rear output shaft can move in and out (back and forth) about 1/8". I have IRO hack-n-tap SYE installed, otherwise I probably wouldn't have been able to notice this. I'm just speculating but it doesn't seem like it should move quite that much.

I've been fighting driveline vibes since I lifted the Jeep 4.5" and am starting to wonder if my t-case may be causing or at least contributing to them. When I bought the Jeep with 145k on it I changed the fluid and it was filthy, as black as ink. It doesn't make any odd noises in 4WD as far as I've noticed. The Jeep is my daily driver so 99% of my driving is in 2WD but I usually put it in full time mode on extremely rainy days when the streets are slick. It's a bit tricky to shift into 4-hi full time and back into 2WD, usually wants to shift into 4-hi part time and stay there, but I use 4WD so infrequently I haven't checked if maybe the linkage just needs adjusting.

The Jeep is a '91 and I'm running a stock front shaft in the rear along with the aforementioned SYE. It's been making both weird noises since I got it bone stock a year and a half ago. I've put 20k miles on it since then. Any thoughts?

the shaft moving in and out isn't too much cause for concern. Does it have side to side play is the more important question.

How's the joints in your shaft look. you say you did the hack and tap, stock front DS in the rear? Did you rebuild it before you swapped it in if so?

the shifting thing might be the pads on the shift fork. It's common. Cheap and easy to fix. The T-case is a good first time driveline project, other than some big c clip tools there aren't any odd things required to rebuild one.

I don't see or feel any side to side play in the yoke. But the in and out play seems like a lot more than what I'd expect to be normal. Maybe I'll see if I can put a dial indicator on it and measure it.

I replaced u-joints in the DS with no change. Could be that the DS is not perfectly balanced? I may have a local shop check it out soon.

Red91Laredo said:

.... Secondly, when driving below 10 or 15 mph I hear a kind of "chuff-chuff-chuff" sound that seems to correlate to each turn of the driveshaft. I thought it was a front wheel bearing or u-joint going out until I noticed the sound had vanished when I had to move the Jeep with the rear driveshaft removed the other day. I just drove it around the block in 4-hi part time so I could pull it into my other driveway and the sound was gone....

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Sounds like your chain is stretched and is rubbing on the case. That would explain why the sound vanished when driving in 4-hi... It kept tension on the chain, preventing it from rubbing.

I think you're right. The noise is kind of like a scuffing sound. Also I stuck my finger in the fill plug the other day to check the fluid level and noticed some very tiny pieces of metal in the fluid. It had kind of a shimmer to it. The noise is getting louder too. For the longest time I thought I had a brake drum out of round, then I swapped to rear discs and it didn't go away.

Looks like a t-case replacement is in the works for this weekend. I'll report back if that solves the issue. I'm just going to swap it out so the Jeep isn't down for too long but I'll be tearing down the old case as well to see what I find. If it's not too bad I'll rebuild it for a spare or to sell, if it's in bad shape I guess I'll have a new 70 pound doorstop.