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Rear end humming

M

MG2000XJ

NAXJA Forum User
Location
Salt Lake City, UT
So last week the jeep started humming. My friend and i have come to the conclusion thats it coming from the rear somewhere. Im thinking its either the pinion bearing or a wheel bearing. Its a 2000 w/ 29 spline 8.25. Im running 33's and have a cv shaft but I drove it on the stock shaft for a while before I got the cv. It only hums from 55 up. MY question is what should I be looking for? I was going to take out the rear shaft and see if it still does it. I have to drive over 8 hours at the end of the week (perfect timing right) so any help would greatly appreciated! Thanks guys, Morgan.
 
So last week the jeep started humming. My friend and i have come to the conclusion thats it coming from the rear somewhere. Im thinking its either the pinion bearing or a wheel bearing. Its a 2000 w/ 29 spline 8.25. Im running 33's and have a cv shaft but I drove it on the stock shaft for a while before I got the cv. It only hums from 55 up. My question is what should I be looking for? I was going to take out the rear shaft and see if it still does it. I have to drive over 8 hours at the end of the week (perfect timing right) so any help would greatly appreciated! Thanks guys, Morgan.
 
Check for any visible leaks from the pinion or axle seals. Also check for play at the pinion and axle the axle shafts. My bet would be on the axle shaft bearings. You're sure it's not the tires, right?
 
Possible pinion bearings going out. Remove the shaft and check for and play up and down, and in and out(sounds perverted, huh).

Another thing is it could be the ring gear. Remove the cover and make sure the carrier adjustment nuts are tight.
 
Before tearing into the rear end, I would pull the rear drive shaft and check the U-joints. If the joints are fine, have a driveline shop check it for balance. This is far more likely to be the problem since it is speed related. Pull the shaft to check the joints. You can't do a good job on the vehicle. My bet is that the centering joint in the dual cardan joint is going bad, with a second being an out of balance shaft.
 
What Tom said. A bearing noise normally starts sooner than 55. I have a bad carrier bearing, and it starts at about 10 mph. When the pinion bearing went it started about then too, but changed pitch when on acceleration vs deceleration.

Neal
 
I read the post on driving without a rear shaft, from what I read I couldnt drive on the front shaft in 4 wheel full-time on the highway for very long without negative affects. I will pull the shaft and check the U-joints and the pinion bearing. I dont have much in the way of automotive knowledge but I have some friends here that are willing to help. I have the basic hand tools and what not so I think I have what I need. It only starts 55 and above and will only stop below 55.
 
The negative effects would be driveline binding. This occures only if you have both drive shafts in, so removing your rear shaft to test is safe from the binding problem. You will need to put it in 4x4 HI to engage the front axle to get it to move, so you will at that point have only front wheel drive. Still take her easy though since you are placing full power through components that only assist the normal "2 wheel drive", drive line in 4x4 mode. It's all safe, but play it safe and don't go crazy on acceleration, just gradually get to the speeds and find out if it still hums or not and get it back together. I'm only ruling on caution because my xj has a very strong throttle response after boring my TB, and can imagine easily spinning tires if I removed the rear shaft. I would first check tire balance and go from there. Good luck on the hum, I hope your friends can get you back to quiet speeds.
 
So I pulled the rear shaft today. U-joints are fine, no leaks around pinion bearing, Sye still tight (hnt style), Drove down the highway got to about 70 without the humming. Im thinking the shaft is out of balance now. Is there anyway to check this myself? Im somewhat new to the area and dont know of any driveline shops. I am going to go on the search for one and talk to some other shops and locals. Thanks for everyones input, I really appreciate it.
 
If you pulled the rear shaft and it stopped humming, then its like to be your ujoints as mentioned. Otherwise your pinion angle on the 8.25 is pointed too far up. I had a bad hum and removed my 4 deg shims and it stopped because my pinion was pointed up a little too high.

should go ahead and replace Ujoints since the shaft is out and they are cheap
 
I dont have any shims and it just started a week ago, if it was the pinion angle wouldnt it have happened way before this? The u-joints are less than 6 months old also.
 
Made the 500 mile drive with the humming the whole time. Took it to the local place I go to today and he said he thought it might be the transfer case. Then he preceeded to talk about swapping cases and re-building them. Is this a possibility?
 
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