NP242 Front Output bearing loose

Ok. So I've had these issues for a while.
I have a 99 XJ NP242.
I replaced the front output bearings due to a very slight up and down movement. There was a bad vibration above 65mph with the 3.55s and 30s.
I noticed that the vibration was gone immediately folliwng the bearing replacement, however it returns soon after about 100 miles.
Now that I have 5.13 gears, the vibration is very noticeable after 55 mph and very intense at 70+mph.
I KNOW that something with the transfer case is messed up because the driveshaft has been replaced, and then sent to a shop, where it was balanced and trued. The front gears were replaced by a skilled shop here in Phoenix.

How can I fix this problem? It seems that even a very very small amount of play in the front output yoke on the transfer case will cause huge vibrations at highway speed. I've resorted to removing the front shaft altogether for the time being.

I've read other threads that suggest replacing the front output shaft due to excess wear where the bearing seats. I can't find a part number for that shaft. It is shown in quadtrac's breakdown of the NP242 but there is no part number.

Has anyone else had this problem? What did you do to fix it?
Thanks!

Are you using a good bearing, ie Timken or SKF? Are you torqueing it to proper level, about 125-150 ft/lb depending on transfer case

I torqued it to 130 ft-lbs.

I used a rebuid kit off ebay. When I noticed some slop in the bearing out of the box, I went to Autozone to look at a Timken bearing, and it had even more slop so I used the one from the kit.

The bearings do not press tightly into the transfer case. Even brand new with a good SKF bearing there is going to be some up and down movement attributed to the way the bearing sits in the case. Not all driveshaft shops do good work. Sometimes they can't balance them very well, or the splines are worn. I have found if you have one driveshaft with worn splines and one with tight splines, the vehicle has more vibrations than if you have two driveshafts with worn splines.

Thanks. Ok so I guess I should get the rear shaft balanced and such also. Maybe both together cause the vibrations. I should just drive the Jeep with the front only in and see if there are vibes?

I would do more inspection and testing before paying for work. If your driveshafts are interchangeable you could try the front in the rear and see how that works (only running one at a time). Unless the rear shaft is obviously bad I would hold off paying for work to it. You might bring both down and explain that you have a vibration, thought it was the front, so I had you go through this one, and it's not any better (or worse), so you've come to them to help you identify and solve the problem. Is there something else in the driveline that could be causing it? Are your driveshaft angles and u-joints all good? And I'll say it again, not all driveshaft shops do good work.

md21722 said:

Are your driveshaft angles and u-joints all good?

Click to expand...

Too much front pinion angle can cause vibrations.
Going from 3.55s to 5.13s multiplies the issue, since the driveshaft is spinning much faster at any given speed.
When I regeared my 2001 XJ to 4.56s, it developed a very noticeable vibration, starting at about 50 MPH. Adjusting the pinion angle to less than 1 degree eliminated the vibration.

I also noticed that when the transfer case is in part time or fulltime 4x4, there is a loud grinding scraping noise. It gets worse the more throttle you give it and the faster you go, and it goes away when you let off the gas. In 2wd the sound goes away.

Desert4x4 said:

I also noticed that when the transfer case is in part time or fulltime 4x4, there is a loud grinding scraping noise. It gets worse the more throttle you give it and the faster you go, and it goes away when you let off the gas. In 2wd the sound goes away.

Click to expand...

That sounds like a stretched chain.

i had a similar noise and vibration on mine when i put a 3 inch lift on it. ended up dropping the transfer case with hockey pucks and the noise and vibration vanished.

maybe try running it with no front shaft on it and see if the vibration and noise are gone.

Thanks for being the impetus for me to validate my suspicion. Due to the full time mode components in a 242, the distance from the face where it bolts to the transmission to the front u-joint centerline is ~5/16" greater than on a 231, extending your front driveshaft by that amount. I suspect this is the reason that people have more vibration issues with a 242 than they do with a 231. They are the same with regards to the front output bearing being a slip fit retained by a ring. The 242 front output bearing is larger diameter and slightly wider, thus it should perform better than a 231, "all things being equal".

You didn't mention your lift height or LCAs, but on my 94 at 4" with a 242 and aftermarket fixed length LCAs, the front driveshaft installed-length is 32.5". Compared against the OEM 30.66" and what I "hear" is a 3" slip joint, the 1.84" longer installed-length is significant. I wince when I think about where the other end of that shaft is in relation to my family jewels and just how little spline engagement there was.

If you decide to replace the front yoke, Crown 4798138 is what you're looking for for a 99...

Not sure why my previous response didn't go through and I'm not much for retying it, but long story short, make sure that your front driveshaft is long enough.