Front end humming

[-AINOKEA-]

Hey all. So my JT recently started humming, seems to be coming from the front end somewhere. Figured it would be unit bearings due to 3.5 BS wheels and 37s but they seem to be alright. This sound is the only thing I could find. It’s coming from inside the front diff. Definitely doesn’t sound normal, but maybe it is. Idk much about this type of stuff with FADs and all that. Anyway, here’s a video of the sound when the front driver tire is spinning. Any help identifying the issue would be greatly appreciated.

edit: front axle is still stock with factory 4.10 gears.

Front Diff Rattle

youtube.com

 

[Disciple Off Road]

From the video it just sounds like the normal noise from the side gear and spider gears spinning. Like you mentioned, you won’t hear this on the passenger side due to the FAD.

If you are hearing a hum or noise while driving at higher speeds or feeling a harmonic vibration, it couldn’t hurt to to pull the cover and inspect the gears. It could also be a sign of a failed or failing bearing.

 

[-AINOKEA-]

From the video it just sounds like the normal noise from the side gear and spider gears spinning. Like you mentioned, you won’t hear this on the passenger side due to the FAD.

If you are hearing a hum or noise while driving at higher speeds or feeling a harmonic vibration, it couldn’t hurt to to pull the cover and inspect the gears. It could also be a sign of a failed or failing bearing.

Thanks! I’ll dive into it this weekend. I’ve been putting off a regear for a couple years now…. Might be time.

 

[kevman65]

You might try pulling the fill plug on the diff and dipping a pinky finger to check level and then smell if it smells burnt.

 

[-AINOKEA-]

You might try pulling the fill plug on the diff and dipping a pinky finger to check level and then smell if it smells burnt.

Thanks. Yeah this is kind of a weird one for me… it sounds/feels like my JKU did but that was due to some play in the front driveshaft. The front DS doesn’t spin on this thing… gonna dive in this weekend and see what I can find. Thanks!

 

[nevrnf]

I had one do the exact same thing after we installed a lift kit. Made the noise for about 20 miles then just stopped. Never happened again in the last year.

 

[sunnysideup]

I remmeber someone early on- with a JT say that they had a bushing go out inside the FAD that then allowed the coupler to "buzz" or "make a growl on the highway... because it did not disconnect enough... so it would make noise as it would slip back against the shaft. I don't remmeber where I read it... but it was a note I put in the back of my mind to consider it the noise ever came up. If remmeber right it was plastic when he found the worn out part.

 

[Lperdue]

I remmeber someone early on- with a JT say that they had a bushing go out inside the FAD that then allowed the coupler to "buzz" or "make a growl on the highway... because it did not disconnect enough... so it would make noise as it would slip back against the shaft. I don't remmeber where I read it... but it was a note I put in the back of my mind to consider it the noise ever came up. If remmeber right it was plastic when he found the worn out part.

Had that happen to me at one point you can remove the fad and pull the shaft and inspect the secondary shafts bushing. You can also put it in 4 Hi and see the sound goes away.

If that is the issue can by a replacement bushing or upgrade to a different shaft. I went to a two piece RCV shaft with a brass bushing and never had the issue again.

 

[jeeeep]

Hey all. So my JT recently started humming, seems to be coming from the front end somewhere. Figured it would be unit bearings due to 3.5 BS wheels and 37s but they seem to be alright. This sound is the only thing I could find. It’s coming from inside the front diff. Definitely doesn’t sound normal, but maybe it is. Idk much about this type of stuff with FADs and all that. Anyway, here’s a video of the sound when the front driver tire is spinning. Any help identifying the issue would be greatly appreciated.

edit: front axle is still stock with factory 4.10 gears.

Front Diff Rattle

youtube.com

I've been fooled that a unit bearing is good because the unweighted spinning tire does not put all the forces of being on the road does.
Grab both sides of the tire and wiggle it, there should be no movement.
Also, remove the wheel and rotate the hub left and right with your hand, you will be able to feel the grinding sandy feeling vs the smooth rotation of a good hub.

 

[-AINOKEA-]

Well.. I don’t have very trained eye but I might know a few things from what I’ve learned here over the years. Everything in the diff seemed to be alright from what I could tell. Think I’m just gonna get a regear done and swap both unit bearings. I’d imagine it’s gotta be the unit bearings with 40k miles on 37s. We’ll see. If that doesn’t work, gotta convince the wife to get me UD60s for Christmas