Jeep Cherokee Roaring Drone Noise

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Nick1994

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Prepare for a long one!
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This is on my grandfather's 1996 Jeep Cherokee 4.0L 4x4 136k miles with the trac-lock limited slip rear-end (Dana 35). The noise is a roaring, droning type of noise. It sort of had a pulse to it. The pulse of the roaring noise fades in and out and each pulse has about 3-4 seconds in between. It's also a vibration that doesn't shake the Jeep but it sounds just like there's a subwoofer in the back just playing pure bass. The noise starts at about 60 mph and stays throughout any speed faster than that. I'm not sure where the direction of the noise is coming from but it sounds louder when in the back seat. It has brand new U-joints for the rear driveshaft (originally thought that was the problem). I changed the front differential oil to Mobil 1 75w90 and the rear to Mobil 1 75w140 (incase the Jeep tows, I found it recommended online). Both oils have the limited slip additive. At the same time the transfercase and transmission were drained and filled with MaxLife ATF. I changed all of these oils 1 month ago. The noise started probably 1 1/2 years ago and it seems to be getting louder, the new fluids made no difference. The noise seems to get louder after driving a long distance on the highway, Saturday we drove it about 110 miles out to the desert and when leaving at the gas station I did a u-turn and there was a howling noise in the rear although it is possible it could be the drum brakes in the rear are over-adjusted and rubbing on the turn(my brothers jeep did this). I will adjust them tomorrow to be less.

I'm thinking it is the rear axle, Perhaps some bearings are worn or something. When replacing the diff-fluid, it didn't look too out of the ordinary, it was quite dirty in the rear but it didn't seem silver to me. The front was pretty clean.

Another thing I need to add is that when doing U-turns it seems like the rear end locks up both wheels and activates the limited slip. I'm also wondering if it is stuck or activates on the limited slip while driving straight down the highway, thus creating the noise.

Tomorrow (Monday) I will get out the jack stands and jack and do some tests. I will check for play in the front wheels to check for wheel bearing play and will adjust the rear brakes to not be so tight (not sure how to word that lol). I'm also going to put the rear on jack stands and put it in drive to see if a tire is wobbling.

I want to make sure it is reliable and safe as when driven on the interstate out of town every 2 months or so it is at 80 mph for 200 miles round trip on the interstate.

This Jeep was owned from new to 100,000 miles by the Arizona Department of Transportation, not sure what they did with it but it has a faded circle on the roof and screws to where a round orange siren was. I assume it was maintained fairly well. My grandfather has owned it since April 2007 and the last 36k miles and has had it's oil changed every 3,000-3,500 miles and maintained well. It does go offroad on some rough dirt roads and does some 4-wheeling. It has always had matching sets of tires since he has owned it, and it currently has a set of 1 year old BFGoodrich All Terrains with about 4,000 miles on them in 235/75-15 size. I have had them rotated and balanced and it made no difference.

Any help is greatly appreciated.
 
Originally Posted By: crazyoildude
How are the tires? I had an suv that sounded like the rear was shot very loud and it was a bad tire
Tires are 1 year old BFG All Terrains. 4k miles. After rotating and balancing the noise didn't change at all. The noise was also on the old set of tires as well.
 
My friend had a Cherokee that had a droning noise. It was the rear end. He put a Ford 9" into it and the noise was gone.
 
The trick question is:

Does the noise go away for a split second with you jerk the steering wheel left or right?
 
Please clarify: you added the correct amount of limited-slip additive, or you're assuming the Mobil 1 has it? Anything I'm reading online says you need to add the friction modifier to a Trac-Loc Dana 35 no matter what lube you use. That probably wouldn't explain the droning noise at speed but it sure would explain the U-turn behavior.
 
I had a similar issue w/ my 97 Jeep Grand Cherokee. The rear diff was grinding badly. Had to replace the rear diff and axle with a used one.

But mind was more of a constant, loud, sound mixed w/ a bit of a grinding noise.
 
I just used the Mobil 1 gear oil since its supposed to already have the limited slip additive in it. I can get the additive from the dealer though. It doesn't make a difference in city driving and turning onto streets or at a light so that's another point off for a front wheel bearing possibly. My brother has a spare Dana 35 axle if this one is toast, unfortunately it isn't a limited slip but oh well. I really don't feel like swapping axles but if that's the issue I'll do it.
 
What Olas said> Get car in the air and listen to each wheel. Sounds like it could just be a bad wheel bearing.
 
Pop the cover off the housing and remove the small hex screw on the carrier, pull the c clips and remove the axles shafts slightly. The outboard bearings are right there behind the backing plate. If the axle shafts have any marks such as pitting or wear then they need to be replaced along with the bearing and seal.

I think you can visually inspect the clutch pack with the cover off also. Don't remember as it's been a while since I had a trac loc apart. Most times a bad clutch pack will also cause odd wear on the spider gears so look at those closely to.

Is this a 249 or 242 transfer case? If it's the 249 (no selectable 2wd mode) then are you sure the tight u-turns aren't just the viscous coupler locking up and causing driveline bind? This is a typical indicator that the viscous coupler's fluid is done (usually done at around this mileage).
 
Originally Posted By: gomes512
Pop the cover off the housing and remove the small hex screw on the carrier, pull the c clips and remove the axles shafts slightly. The outboard bearings are right there behind the backing plate. If the axle shafts have any marks such as pitting or wear then they need to be replaced along with the bearing and seal.

I think you can visually inspect the clutch pack with the cover off also. Don't remember as it's been a while since I had a trac loc apart. Most times a bad clutch pack will also cause odd wear on the spider gears so look at those closely to.

Is this a 249 or 242 transfer case? If it's the 249 (no selectable 2wd mode) then are you sure the tight u-turns aren't just the viscous coupler locking up and causing driveline bind? This is a typical indicator that the viscous coupler's fluid is done (usually done at around this mileage).
It's the 231 transfercase.
 
Well, bad news. I jacked up the rear, removed the tires and brake drums to eliminate any noise that can come from them and started it up and put it in drive. I drove it up to 75-80 mph and that's where it started doing the vibration bass noise. It also has an annoying whine to it as you can hear in the video. I recorded it with my iPhone right underneath the jeep while doing this so the audio isn't the best and I don't think it can pick up the vibration bass noise. All I know is there's something wrong in there. It's out of commission for interstate driving for now until we swap another axle under there.

And just for the heck of it I put the 02' Trailblazer on jack stands too and did the same thing as took it to the same speed. It had a little whining noise but I think that's normal and it had no
vibration or bass noise at all.

http://youtu.be/k51cPwiYqMM
 
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