The Growl of the NP231J - new member

Hello all. I’m a new member to as of today 7/17/20, but I’ve owned a ‘95 XJ since the day it was new on the lot. It was my company vehicle, then my vehicle, then my mom’s vehicle, and now it has been mine again since August 2016. My mom was hardest on it, putting 9000 miles on it in 14 years.

I have what seems like a minor problem at this time, but I know it will get worse if I don’t get it resolved. Plus, I want this thing to be as reliable as it can be...


So here’s the issue; 1995 Jeep Cherokee SE 4x4, 4.0L Auto Trans, NP231 Txfr case, approximately 170k miles. At least a year ago, I noticed if driving ON-road in 4wd HI, I have a growling noise during acceleration or deceleration that seems to be coming from the transfer case. If I’m just maintaining speed, it’s very slight. The growl in deceleration is not quite as loud as during acceleration. I can’t find any play in the front driveshaft, axles, or at the output shaft of the case going toward the front end. I did change the txfr case fluid, but the old fluid looked good. Used O’reilley’s DexIII / Mercon. I also get the growl when I accelerate in 4wd LOW, but the stress of acceleration is brief, so the growl is brief, but it’s still there.

I get no noise accelerating or decelerating in 2wd, so I know it’s the txfr case or something in the front end. I have not changed the front differential oil in the front end, but it’s not low and does not appear to be contaminated. I did put a new hub and axle shaft u-joint on the right front about two years ago. Left front hub and u-joint are original.

I’m afraid I may have an internal bearing In the txfr case failing, and I don’t know if I’m up to that level of repair. Anything else I should check for?

Thanks in advance.

Before you make assumptions remove the front driveshaft and drive in 4x4. If the noise goes away it's not your t-case and I would get the driveshaft serviced before looking at the diff. BTW, that's not high mileage for a XJ.

I have dropped the front driveshaft and performed a test drive. The growl is reduced a lot, but it’s still there. I’m guessing the same thing is growling, but not as loud because there much less torque stress without the front axle connected to the transfer case.

While I had the front driveshaft out, I decided to replace all three u joints since they were all original There was no noticeable play anywhere, but when I got to the inside Ujoint of the double Cardan, it did have a dry cup. I reinstalled the driveshaft and the Jeep is smooth a silk up to 75 mph with the driveshaft spinning (but not in 4wd), but I still have the rumble / growl under acceleration in 4wd.

It’s not terribly loud, but very easily noticeable especially from about 25 mph up to about 40 mph. It actually gets a little less noticeable faster than 40, but I think that’s because I’m not accelerating nearly as hard. I don’t run it much over 40 in 4wd. Once I’m at 35 - 40, I can back off the throttle just enough to maintain speed, and the growl almost goes completely away. When I let off the throttle, I can hear it again during engine braking deceleration, but not quit as loud as during acceleration.

The hardest part about doing a 231 is just finding good parts otherwise it's a simple job to replace anything (other than the sun gear).

Grab the front output yoke on the tcase and "wiggle" it. Is there excessive slop? The front output shaft roller bearing can cause this noise.

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Are you driving in 4x4 on dry pavement ?


The NP-231 does make a noticeable mechanical noise as it operates in 4x4. Have you compared your Cherokee to any other Cherokee ? Just because you hear a noise does not mean that there is a t-case malfunction.

Now that you have removed the front driveshaft and performed a test drive in the same manner that makes the noises, re-install the front, remove the rear driveshaft and repeat the test drive. Inspect the rear driveshaft u-joints.

What is the age and condition of the motor mounts and the transmission mount ? Are any exhaust hangers failed, or is any part of the exhaust torquing enough to make contact with the uni-body or the trans cross member ?

Open each differential and inspect for wear and fluid condition. Check the end-play on the pinion yokes. Inspect the D30 unit hub bearings for excessive wear.




My Cherokee #7 has +284,000 miles and no t-case issues. My "new" Cherokee #8 has 181,000 miles and no t-case issues.

checked the transfer case fluid level and condition?

Doesn't hold much.....

SlowXj said:

Grab the front output yoke on the tcase and "wiggle" it. Is there excessive slop? The front output shaft roller bearing can cause this noise.

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There is zero slack in the front output shaft. There is a tiny bit of slack in the splines of the slip yoke on the rear driveshaft. I don’t think the slack in the slip yoke splines are creating the noise since it’s not present in 2wd, but I’m not through testing on that yet.

Tim_MN said:

Are you driving in 4x4 on dry pavement ?

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This is the first thing to not do to a 231

Tim_MN said:

Are you driving in 4x4 on dry pavement ?


The NP-231 does make a noticeable mechanical noise as it operates in 4x4. Have you compared your Cherokee to any other Cherokee ? Just because you hear a noise does not mean that there is a t-case malfunction.

Now that you have removed the front driveshaft and performed a test drive in the same manner that makes the noises, re-install the front, remove the rear driveshaft and repeat the test drive. Inspect the rear driveshaft u-joints.

What is the age and condition of the motor mounts and the transmission mount ? Are any exhaust hangers failed, or is any part of the exhaust torquing enough to make contact with the uni-body or the trans cross member ?

Open each differential and inspect for wear and fluid condition. Check the end-play on the pinion yokes. Inspect the D30 unit hub bearings for excessive wear.




My Cherokee #7 has +284,000 miles and no t-case issues. My "new" Cherokee #8 has 181,000 miles and no t-case issues.

Click to expand...

Noticed the noise on dirt, driving on a smooth section between big mud holes. I’ve been testing the acceleration noise on a gravel road nearby. I’ve done some slow rolling in a straight line on a section of new asphalt near my house to see if I can hear anything just rolling, not accelerating or decelerating.

I haven’t compared it to anything except its former self, since I started driving it with about 5 miles on it and stopped driving it with 151k, then started driving it again with 160k. It definitely did not make this noise in its past, but it’s not an extreme noise. It’s just a rumble / growl.

Motor mounts and transmission mounts are original / 25 years old, but don’t seem to have any excessive play. It does not appear the exhaust has ever touched the cross member. I’ve been under there enough to have noticed . I have changed out the lubricant in both differentials. The rear D35 howls a little, which has been the case for at least 18 years / 20K miles. Right hub & axle u-joint has been replaced since Aug 2016. Left hub is original.

The one thing I have not done is drop the rear driveshaft and drive it with the front doing all the pulling. It did occur to me that the front driveline might have less slack than the rear, and when I accelerate with the front end engaged, it takes most of the load and allows the slack in the rear driveline to to remain “unloaded” , which allows it to rattle around some. I may het do that today.

Fluid level?

On a 95, you'll need to find a way to seal up the tcase output before doing that, the rear shaft's slip yoke is part of what keeps the fluid in.

cruiser54 said:

checked the transfer case fluid level and condition?

Doesn't hold much.....

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Changed a couple months ago whenI first started noticing the noise, but it was full and what I drained out was clean. I think I had previously changed the fluid in fall of ‘17.

cruiser54 said:

Fluid level?

Click to expand...

All good & fresh.

Rob Mayercik said:

On a 95, you'll need to find a way to seal up the tcase output before doing that, the rear shaft's slip yoke is part of what keeps the fluid in.

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Found out the hard way. Didn’t lose much, didn’t have to go far to know the growl is still there. Took about 1/2 quart to refill.

With the rear driveshaft out, the noise is different, and slightly worse. It’s also worse when decelerating. It’s still not extreme, and might be normal for the wear. It also seemed to have more slack in the driveline when running on front only. Accelerating and letting up on the throttle came with a very noticeable clunk as the the front driveline changed load.

It’s definitely much more noticeable than in the past, but the rig probably wasn’t put in 4wd more than 3 or 4 times in 14 years. It was driven about 10-15 miles a week (beauty shop & grocery store) by my mom until she passed away. I bought it back from my siblings.

I have seen some mention about running lightweight synthetic engine oil in NP 231’s to mitigate some noise, but I’m not convinced anything going on in this txfr case is related to the lubricant in the case. It could be related to lack of use, but it’s always been full of fluid when checked / changed.

I may have to live with it a while.

Sorry about the rear driveshaft and the fluid, I forgot that the older 231 have the seal on the driveshaft yoke. IRRC the temporary quick fix is a plastic OJ or Lemonade can.

Since you know the entire maintenance history, the sounds are likely just age/mileage and IMO monitoring the sounds is probably all that is necessary.

Noise is probably the front output bearing. The front yoke is right behind the drivers tire, so it picks up all the road trash. It goes out pretty quick relative to everything else in the transfer case.

ehall said:

Noise is probably the front output bearing. The front yoke is right behind the drivers tire, so it picks up all the road trash. It goes out pretty quick relative to everything else in the transfer case.

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Might be the rear roller bearing on the front output shaft, but it’s not the ball bearing at the front end of the front output shaft. It has zero play / slack in any direction.