Rear axle replaced, now humming under light throttle

[merc3065]

As the title says…
2021 rubicon diesel. 48500km at time of original problem, currently at 55500km still under warranty.

bit of back story…
Driving down the highway in 2wd when the service 4wd light started flickering on and off. Had the rear axle locker system fail on the rear axle saying service 4wd system. First problem the dealer found was a bad wiring harness in the cab behind the rear seats being pinched, chafed and damaged. Replaced the harness and the issue went away. Second time this happened, I used the rear locker once in a bad snow storm to pull my wife’s car back onto the road. Worked well even at idle. Disengaged the locker and service 4wd came up again. Knowing about the sensor problem being contaminated with diff oil, I brought the TSB to the dealer and asked if they would check it for that issue. Mechanic diagnosed it as a failed solenoid. And told me that the only way to repair this was to replace the whole axle assembly. Wouldn’t even humour me on the sensor issue.
So the axle was replaced with a new one at 48500km.

About 5000km added on (53000km) regular hwy driving no issues until I started to hear a loud hum but only in town around 55-65kph. At 55000km I started to notice it getting louder at the above speeds, but quieter the faster you go. Very noticeable with light throttle. If you coast, the hum goes away immediately. Give it harder throttle, the hum is not as noticeable or drowned out by the engine noise. Shift car into neutral no hum, forced downshifts/up shifts at 55-65kph with no change to the sound or pitch.

Checked the drive shaft and there’s no play end to end. Checked the diff oil and it’s grey. The top magnet picked up a couple bits of metal. So returned it to the dealer and explained the issue. Showed them the metal bits (taped it to a piece of white paper). Unfortunately they couldn’t reproduce the sound and told me it was tire noise because the front tires have a little bit of cupping on the outside of the tread. So they humoured me and I took them out on a test drive. Within 2mins I was able to reproduce the sound and then the mechanic heard it and I explained and showed how to reproduce the sound. He agreed there was a humming sound.

Now to the question:
1) is it normal for new diffs (in this case whole axle assembly) to turn fresh gear oil grey and metallic looking during break in? Should there be little bits of metal .5-1mm in side floating around in the oil or on the magnets?

2) when installing a factory axle assembly, do you still have to set the proper backlash on everything (ring/pinion, carrier etc) or is it good to go right out of the box?

Everything I am reading, and my limited understanding is pointing to something to do with the pinion not properly setup to the ring gear.

I’m considering asking them to drop the cover off and inspect the rear diff and inspect. At the very least it will clear out the grey oil and fine particles and allow for an inspection.

Looking for advice and thoughts on what to do next as I can’t have my truck down for much longer (coming up on 2 weeks of “diagnosis time“).

Sponsored

 

[ScottLars]

I have noticed the same hum. I notice it mostly above 60 mph and under light (barely pressing) the throttle. Coasting or giving more throttle makes it disappear. Also does not matter which gear it's in.

I had the passenger rear axle assembly replaced about a year ago for leaking seal. Installed new diff covers a couple weeks ago and found similar conditions in the oil a few small bits of metal on the drain magnet. I briefly inspected ring gear the best I could and did not see anything that stood out.

Just the weekend I replaced brake pads an when I had the driver's side rear caliper off noticed a small amount of end play (in and out) in the axle, maybe 1/16" of an inch.

Wondering if this could be the source of the hum....

 

[merc3065]

Update for my post:
Dealer put the truck up on the lift and found the sound to be a bad pinion bearing. Once they had the diff out they also found the carrier bearings had started to fail. They couldn’t tell me the cause of the failure.

Bearings were all replaced and new ones reinstalled. Now another 4000km (kept it light use after the rebuild) and the humming is coming back again. The dealer is going to “call around” to find out what to do as my 60000km warranty is about to expire

This only showed up after the axle was replaced which is unfortunate as the dealer has been helpful trying to get things right.

Hopefully the dealer will have an answer shortly. Personally I would think that if the problem is coming back at so few KMs, there’s probably something wrong with the axle assembly that was replaced and my thoughts would be to swap out the axle again.

 

[dmwphoto]

Swapping out the assembly makes good sense

 

[merc3065]

Back to the dealer, went for a drive with the service manager and was able to reproduce the sound but he is afraid to down the truck again because it’s not as noticeable as when the bearing was failed. At least it’s documented and was asked to keep driving it and monitor for if it gets worse. Called JeepCares and got a case# for documentation so it’s at least on record now as an ongoing problem.

Checked the rear diff oil, it wasn’t silvery like the first time, but it’s grey which doesn’t seem like it should be. It reminds me of when water mixes with oil. Going to let it sit for another couple hours and recheck to see if it’s changed.

 

[SIG551-A1]

That is not good. They are not setting the preloads properly in the pinion and/or diff bearings.

 

[merc3065]

Just finished changing the front diff oil, oil w/ filter, fuel folter. and xfer case.

Front axle at 60000km (left), rear axle at 4000km (right).

Looks like some kind of contamination occurred on the rear diff, but I can’t see from where since there’s no leaks and the breather tube is still intact and in place too. No leaking axle seals either.

Dealer is working with me on it but hoping to avoid rebuilding this rear axle assembly but lowest cost will probably prevail.

 

[merc3065]

Finally back after a while for work. Hopefully last update on this issue.

Oil contamination was supposedly due to synthetic grease that was used during reassembly. So the dealership inspected, cleaned and refilled the diff. Road tested for the noise but failed to identify my concern. Dealership was adamant it was my front tires causing the noise due to cupping. So I said nuts on it and had them replace the tires.

Fast forward 6 months, back home from work and not 100kms later on a brand new set of tires, same noise from the rear diff.

I let the dealer know again that the new tires did not fix the noise and that the same noise as last time the pinion bearings failed. So after taking mechanic for a drive, he confirmed the noise. They hooked it to a chassis ear and confirmed pinion bearing noise. They checked pre-load on the pinion and found that it had backed off somehow. So they re-tightened the pinion but and said it cleared up the noise.

I will monitor this and check on the diff oil for metal contamination for the next little while but the noise is gone for now.

Long story short, the diff was not properly setup properly causing incorrect bearing preloads causing pinion bearing noise on light acceleration.

 

[rharr]

You can't really just re tighten the pinion, it's got a crush sleeve in it, and that get replaced if retorquing the pinion so it can set the proper load against the bearing.

To me this sounds like the dealer doesn't know how to setup a axle.

 

[Panthers65]

I've got an identical sound coming from my Diff, but it only started after I regeared the axle.

First regearing attempt and I over-torqued the Crush Sleeve and I knew I did. Had the "UFO Sound" between 35 and 55 MPH. I just replaced/rebuilt the pinion and carrier bearings Sunday afternoon and it made no change to the sound. On Sunday I made sure to SLOWLY creep up on the correct pinion rotational torque and stopped at 15 in/lb (spec is 13-21). The tail bearing in these axles is some funky ball bearing hybrid design to give you .1MPG better.... and it's known to be finiky. Erroring on the low side of the preload is best for these bearings.

At this point I'm crediting the noise to the higher 5.13 gears in the axle. I'm rotating the tires tonight to try and remove the noise, but at this point I"m 100% positive the pinion torque is correct.

 

[JTGuy]

I had mine re geared to 4.88s and they are silent. Dana Spicer gears. The don't know what they are doing.

 

[kennyglm]

has anybody ever figured this problem out to eliminate the noise ? I have the same noise been chasing it for almost a year now.

 

[scoobycarolanNC]

OP, your new and rebuilt axles need to be broken in like a regear job. Metal and stuff is normal.

I just had spicer 4.88s installed by East Coast Gear Supply. Heavy humming on the throttle from 45-55. They tore out the gears and completely rebuilt it under warranty (great shop), same sound. I'm getting the feeling there are a lot of noisy advantek m220s out here.

 

[merc3065]

OP, your new and rebuilt axles need to be broken in like a regear job. Metal and stuff is normal.

I just had spicer 4.88s installed by East Coast Gear Supply. Heavy humming on the throttle from 45-55. They tore out the gears and completely rebuilt it under warranty (great shop), same sound. I'm getting the feeling there are a lot of noisy advantek m220s out here.

Thanks for replying, unfortunately due to incorrect installation procedures from the shop, it was failed bearings and bearing race/bearing coating floating around in the diff oil. Not normal wear. The truck is going back in to have the bearings replaced again because of a failed installation procedure. My concerns are more with whether or not they are going to check the wear on the gears and replace those if necessary.

First time was nearly catastrophic (pinion and carrier bearing races were shredded).
Second time it went in was shortly after the rebuild when I was about to put the truck into storage for 8 months, the oil had emulsified with something (likely water? parts cleaner? synthetic grease on the bearings?) and the bearing noise was very prevalent. Dealer told me that it was tire noise so I had the tires replaced, but when I got back, the noise was still there. They inspected it and determined that the pinion lost preload (less than 5000km from the diff flush and clean). They tightened the pinion nut back to spec and sent me on my way.

This third time the noise occurred again at less than 5000km and they are going to replace the bearings again. They reset the preload, ordered "parts" (I'm not sure what) and now I am playing the waiting game.

All three times, the noise was confirmed with a chassis mic (twice by dealer, once on my own before dealer confirmed) that the pinion bearing was moving around when it shouldn't.

I wish I could say it's normal and it will go away, but not when there is flakes of metal floating around and a very apparent noise.

 

[merc3065]

Hopefully last update. Dealer is replacing the entire axle assembly again under warranty.

I am not familiar with these axles, however what they are telling me is that when the axle assembly ships, it comes with everything installed, including the yoke that goes onto the pinion gear. If what they are saying is correct, then the first axle assembly shipped with incorrect preload or something happened when the mechanics transferred parts from my original axle.

I doubt I will ever know what the real cause was, but it seems like the preload was never set right from the very start. Possibly something to do with the front pinion race/bearing not seating properly during install and setting preload.

Sponsored