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Loud deep humming @ 70MPH on stock 99 XJ

C

Computerbob

NAXJA Forum User
Location
Maryland
I'm getting a loud deep humming right @ 70 MPH and on. I'm not getting pedal or steering vibration just a low frequency hum. The front drive shaft is brand new and the front differential and transfer case were replaced with relatively newer used parts. The tires are brand new on the stock "Snowflake" Limited rims. I was told I need a "Bearing Kit" for the front end and it was a common problem on XJ's.

If this is so what do you all think and where can I get a decent kit for around a $100?
 
Who did the work? I would check it.

Bearing kit you mean wheel bearings? You should check those. But they would make noise about about 30 or so.

Take a VERY good look at your tires, rotate them back to front and see if the noise changes.
 
This issue could be a million things, but I'd check the wheel bearings and balljoints first. I had a wheel bearing that would start making an extremely loud humming noise exactly like you describe at about 80MPH on my MJ. A few weeks after I replaced it, I got an even louder humming (to the point that it could be felt and heard) from a badly shot lower balljoint on the passenger side at about 75-85MPH.

As Skreed said, give rotating the tires a try, while you have the fronts off the ground, check the unit bearings, balljoints, and steering.
 
Yeah sorry, Its a shot in the dark considering all things involved!

I'm getting new rims and tires. If that doesn't fix it, ill get new ball joints then go bearings. That sound like the right steps?

The make a kit that has all the bearings in the differential I was told.
 
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I wouldn't bother with new rims and tires as a first step, unless you're just borrowing them from a friend. That's a pretty expensive thing to try.

I wish I could narrow it down more, just kinda tough to do over the internet :( You seem like you're on the right track though. Don't just replace stuff, check it first - balljoints and bearings are easy. Jack the wheel up, grab it at 12 and 6 oclock, try and shake it (in/out at top and bottom.) If it wiggles more than a little (use your judgement) your balljoints could be toast. Grab it at 3 and 9 oclock, if it wiggles here as well, your unit bearing is probably toast. Also try using a mechanic's stethoscope on the steering knuckle from the backside (right near the U-joint) while spinning the tire. If you hear significant grinding noises, you almost certainly need a new unit bearing.

If you need unit bearings, get Timken ones, accept no substitutes. Similarly, Spicer balljoints are about the only brand you should go with. Moogs used to be pretty good but I've heard from a lot of people recently that they are starting to suck and wear out quickly.
 
Bringing this back from a few weeks ago as I'm having a similar issues.

1998, automatic, 4WD, D30/8.25, stock. Once I get above about 65 I get a deep pitched humming sound that I think is coming from the back. It's not a constant, it's more of a repeating sound that comes and goes in rhythm. No vibrations. Sound is present both under acceleration and while coasting, up and down hill.

Help me develop a list of what this could be and the items to check for in each case. I have read enough of these posts to realize many have this problem and if we can get a checklist of what to look for that could help with process of elimination. This sound is driving me nuts and I feel bad for back seat passengers as it probably makes their head feel like it's in a pressure chamber.

Off the top of my head, these could be the issue.

Rear DS U-Joints - Can remove DS, if noise stops either bad u-joints or out of balance
Rear DS out of balance - Same as above
Rear Wheel Bearings - Not sure how to test
Pinion Bearings - Remove DS, test for play in the pinion shaft???
Carrier Bearings - Not sure how to test
 
Last edited:
BruceB83 said:
Bringing this back from a few weeks ago as I'm having a similar issues.

1998, automatic, 4WD, D30/8.25, stock. Once I get above about 65 I get a deep pitched humming sound that I think is coming from the back. It's not a constant, it's more of a repeating sound that comes and goes in rhythm. No vibrations. Sound is present both under acceleration and while coasting, up and down hill.

Help me develop a list of what this could be and the items to check for in each case. I have read enough of these posts to realize many have this problem and if we can get a checklist of what to look for that could help with process of elimination. This sound is driving me nuts and I feel bad for back seat passengers as it probably makes their head feel like it's in a pressure chamber.

Off the top of my head, these could be the issue.

Rear DS U-Joints - Can remove DS, if noise stops either bad u-joints or out of balance
Rear DS out of balance - Same as above
Rear Wheel Bearings - Not sure how to test
Pinion Bearings - Remove DS, test for play in the pinion shaft???
Carrier Bearings - Not sure how to test
Click to expand...

You're describing somtehing I've been hearing for a while.I'm curious about this as well......
 
my bet is on wheel bearings. My MJ does the same thing but only when I hit 87 or so. If I dare to take it to 95 (did it to see if it would get better or worse) the thrumming goes from repeating to constant.

I guess you could open the diff and remove the spider gears (leave the side gears in though) and then put the cross shaft back and take it for a drive, but by that point you are fairly close to just inspecting the bearings. They will be pitted if they are at fault for that kind of a noise.
 
I am going to replace my rear DS u-joints Saturday as that may be the issue. I can't feel any play so I'm not too optomistic about it.

If that doesn't solve it, I'm inclined to say screw it and throw in a D35 that I have laying around. May sound crazy but this XJ isn't for wheeling, only 4wd usage is for snow and forest service roads if they get hairy. Plus, it has an Aussie locker in it and that would get me the traction aid I'm looking for.

Chasing down a noise that could be coming from many places in a stock axle doesn't sound appealing to me when I could take 1 hour and just replace the axle.

One more thought that I didn't mention in my earlier post, is it possible the noise could be coming from the wheel/tire? I would think I would gradually hear the noise build as opposed to coming on around 65 mph.
 
kastein said:
I guess you could open the diff and remove the spider gears (leave the side gears in though) and then put the cross shaft back and take it for a drive, but by that point you are fairly close to just inspecting the bearings. They will be pitted if they are at fault for that kind of a noise.
Click to expand...

What is that gonna do?

Wheel bearings will still turn...?
 
kastein said:
my bet is on wheel bearings. My MJ does the same thing but only when I hit 87 or so. If I dare to take it to 95 (did it to see if it would get better or worse) the thrumming goes from repeating to constant.
95 in a Jeep......lol.

Is there a way to test wheel bearings other than just replacing them?
Click to expand...
Click to expand...
 
I would not put a d35 in for any reason, but hey, if you want to...

It's pretty easy to inspect the bearings. Pull the axleshafts, look at the wheel bearings. Replace if bad. While they're out, try spinning the carrier, if you can feel a bit of grinding or uneven resistance, look at the bearings. Try moving the pinion yoke, if it has appreciable play replace the bearings. Put it all back together.

EDIT:
MoparManiac said:
What is that gonna do?

Wheel bearings will still turn...?
Click to expand...
yeah, but the carrier and pinion bearings won't. So if the noise goes away, it's one of those, if it stays, it is the wheel bearings.

As for 95 in a jeep... yep, done it. I've had mine up to 120 (straight, flat, open highways with very light traffic late at night ONLY) and it isn't really that bad. No way in hell I would do that kind of speed without having an absolutely empty road I know like the back of my hand though.
 
It could be a number of things. My first guess is either tire balance/wear or rear driveshaft out of balance.

Pull the rear driveshaft and run in 4wd. If the noise goes away, it is the driveshaft balance. Also when the driveshaft is out, check the rotational lash in the pinion.

NEVER just start thowing parts at the problem. Take it to an alignment shop and have them check the balance all the way around. Pay for a diagnosis, then if they do the repair, hold them to it. If they don't fix it, don't pay for it. Around here we look for a shop that uses Bear Alignment tools. If you don't have a locker, they can do an on vehicle spin balance. It will allow them to find the problem easier. If they run Bear equipment, they probably don't have a teenager doing the diagnosis.
 
Good idea on rotating the tires. Like you said, it sounds like a bad ujoint in the rear driveshaft based on my experience.
 
kastein said:
I would not put a d35 in for any reason, but hey, if you want to...

It's pretty easy to inspect the bearings. Pull the axleshafts, look at the wheel bearings. Replace if bad. While they're out, try spinning the carrier, if you can feel a bit of grinding or uneven resistance, look at the bearings. Try moving the pinion yoke, if it has appreciable play replace the bearings. Put it all back together.

EDIT:

yeah, but the carrier and pinion bearings won't. So if the noise goes away, it's one of those, if it stays, it is the wheel bearings.

As for 95 in a jeep... yep, done it. I've had mine up to 120 (straight, flat, open highways with very light traffic late at night ONLY) and it isn't really that bad. No way in hell I would do that kind of speed without having an absolutely empty road I know like the back of my hand though.
Click to expand...

Actually I'd probably go to the JY and pickup another 29 spline 8.25 before I put this D35 in.

I'm going to run by a local tire shop as soon as I leave work and have them check the wheels/tires for balance. I'd like to pull the rear DS and drive it but the noise is happening above 55 and I didn't think you were supposed to drive it in 4wd over 55. Not to mention, don't you need some sort of plug for the tailshaft to prevent it from spewing fluid?
 
Skreed said:
Rotate your tires see if the noise changes or moves.



Sounds like u joints or DS out of balance.
Click to expand...

Just had this thought, because if it was the wheel bearing wouldn't the noise be more constant instead of in and out?
 
BruceB83 said:
Actually I'd probably go to the JY and pickup another 29 spline 8.25 before I put this D35 in.

I'm going to run by a local tire shop as soon as I leave work and have them check the wheels/tires for balance. I'd like to pull the rear DS and drive it but the noise is happening above 55 and I didn't think you were supposed to drive it in 4wd over 55. Not to mention, don't you need some sort of plug for the tailshaft to prevent it from spewing fluid?
Click to expand...
4hi you can drive "any legal speed" in, as long as there is sufficient slip in the road surface. Without the rear shaft you don't have to worry about only driving on loose surfaces, but don't do it a lot and try to avoid heavy throttle usage to keep from stretching the chain.

4lo you are restricted to (iirc) 45-50 and under.

You can simply pull the shaft on a 96 or newer, but yes you need a 1L coke bottle and some duct tape to keep the fluid in on 95 and older cases.
 
Just rotated the tires and the noise now seems to have moved towards the front of the vehicle. The guy at the tire place said if I wasn't experiencing any vibrations than he would be completely shocked if they were out of balance causing that noise. He looked at the tires and said they looked old due to the dry rotting and cracking and told me that if the noise moved up front he thinks the tires are just bad. Either replace them or ride it out he said.

Well I guess I have bad tires. I'm probably still going to replace the u-joints in the rear DS on Saturday just b/c I already have them but I think I've eliminated the possibility of bad wheel bearings.
 
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