Front Differential Gear Whine on Deceleration - Yukon 4.56

Lifted L5P

De Re Metallica
Mar 6, 2021
19
0
1
Montana
Greetings everyone. Have a 2019 CC SB 4x4 Duramax with a 4-inch differential drop lift kit and 35 inch tires (305/70R18). Changed out the stock American Axle Manufacturing (AAM) 3.73 axle ratio ring & pinions to Yukon 4.56’s to properly turn my 35’s and get my towing performance back. Also included full master install kits both front and rear including all new bearings, seals, etc. Rear end went perfect ... both times ... no issues. Front end ... not so much. Actually ... went from the stock AAM 3.73 to Nitro 4.30 to Yukon 4.56 (Yukon does not offer a 4.30). Pulled the Nitro gears because I thought the gears were causing the front differential gear whine issue, but now I am having the exact same problem with the Yukon gears. I can only hear the gear whine between 38 mph and 50 mph, with the loudest whine occurring at 45 mph. It is NOT a loud / constant gear whine noise (I have heard those before). It also only occurs during deceleration or very lightly pressing on the accelerator. The two sets of gears have been installed by two different yet experienced mechanics, who install axle gears a couple times a month on average. The part I can’t figure out ... exact same sound, within a similar speed range, two slightly different gear ratios, installed by two different yet experienced mechanics, and Koyo bearings on the first installation vs Timken bearings on the second installation. Since it only occurs on deceleration or very light throttle, we figured it was caused by a loss of pinion preload. But unfortunately the pinion preload was still within the manufacture’s specification range when checked, after both installations. Also heard a common issue is accidentally installing the pinion bearing race at a slight angle into these front differential cases since they require hammering the race into place inside of the differential case due to limited access regarding pressing the race in. Can’t verify the validity of this issue, but was told this by Yukon tech support. We also pulled the differential covers, checked the wear patterns, checked preloads, etc. ... everything looked good. Kind of at a loss at this point.

Has anyone experienced this same gear whine issue with the 9.25” IFS front differential axle in our trucks ?

If so, what did you find was causing the issue ?

Is this a somewhat common issue with 4.56 and lower gear ratios ?

Is a lower volume gear whine in a specific speed range something I really need to worry about regarding a future parts failure or reduced service life ?

Thank you for the pending feedback ... any helpful & friendly insights are greatly appreciated.
 
Last edited:

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
18,299
488
83
Phoenix Az
whats the gear pattern look like? are you driving around in 4wd during this or 2wd? did you properly break the gear set in once installed? are sure its not the pinion seal squealing? i know in previous posts you said the pinion angle was corrected for a DC driveshaft, it is for sure 100% within 0-2* working load on the ujoints in any direction?

whine comes from how the setup/break in was done, the gears then wear a funky pattern and create the whine. once they whine, it will not go away no matter how you set it up.
 

Lifted L5P

De Re Metallica
Mar 6, 2021
19
0
1
Montana
whats the gear pattern look like? are you driving around in 4wd during this or 2wd? did you properly break the gear set in once installed? are sure its not the pinion seal squealing? i know in previous posts you said the pinion angle was corrected for a DC driveshaft, it is for sure 100% within 0-2* working load on the ujoints in any direction?

whine comes from how the setup/break in was done, the gears then wear a funky pattern and create the whine. once they whine, it will not go away no matter how you set it up.

Unfortunately we were so busy analyzing the wear pattern that I wasn’t smart enough to remember the pictures ... but I am pulling the differential covers again later this week and will be sure to take lots of pictures ... need them to get my replacement gears from Yukon.

I can however tell you that the patterns were good on the drive side and the coast side from what I could tell. They were both centered and appeared to be the same length as well. No toe-heel, heel-toe, heel-heel, toe-toe wear patterns.

Also, the truck made this gear whine sound the very first time it got to the 40 to 50 mph range. Not something that came later or has changed in volume over time.

Also broke the gears in per Yukon’s recommendations. Drove ~ 10 to 15 miles at slower speeds to get the gears up to a proper break-in temperature ... then let them completely cool down. Did this a couple times per Yukon’s specifications. Then only drove to work which is 15 miles each way every day at stop and go speeds under 55 mph accelerating slowly for the first 500 miles. Then replaced the gear oil as recommended per Yukon’s specs. Have not done the towing break-in yet.

Then took the truck out to the salt flats earlier this week and did the same break-in procedure in 4wd ... was out there half a day ... most of it spent waiting for the front differential to cool back down between runs in 4wd.

The transfer case tips upward at a 6.8 degree angle. The front differential was then tipped so the pinion points directly at the transfer case front output slip joint connection. Then a double cardan drive shaft was installed. The front differential drop brackets are custom, cut on a plasma table and bent with a hydraulic break ... installed ... realized the angle was slightly off ... recut with plasma cutter, re-bent with the hydraulic break, then reinstalled. Angle is within 0.2 to 0.3 degrees. Had this done by the best fab shop locally that builds jeeps for Moab ... and checked the angles myself with my digital angle finder.

As you can see the break-in procedure has done correctly (except towing). As for the wear pattern ... I will post the pictures hopefully later next week when we pull the differential covers again.

Never heard of a pinion seal squealing ... how do I identify that is the problem ... and how do I fix it ?

Appreciate the feedback and taking the time to respond.
 
Last edited:

bimmer95

Member
Mar 15, 2019
66
6
8
Morgantown Pennsylvania
Is the front diff disengaging in 2 wheel drive like it should?If it's working properly the only rotating parts in the front diff are the spider gears and the output shafts.Unless you changed out the right axle shaft to a fleece tuff shaft style that basically deletes the disconnect.In which case there would be more noise then stock setup.Also have you ruled out the possibility that it's coming from the rear diff?

Sent from my SM-G981U using Tapatalk
 

Lifted L5P

De Re Metallica
Mar 6, 2021
19
0
1
Montana
Is the front diff disengaging in 2 wheel drive like it should?If it's working properly the only rotating parts in the front diff are the spider gears and the output shafts.Unless you changed out the right axle shaft to a fleece tuff shaft style that basically deletes the disconnect.In which case there would be more noise then stock setup.Also have you ruled out the possibility that it's coming from the rear diff?

Sent from my SM-G981U using Tapatalk
The 4wd is operating correctly ... verified proper operation earlier this week when only the back tires spun on the wet salt flats in 2wd ... and in 4wd could feel the front axle / transfer case engaged ... plus I could distinctly hear the normal light hum of the transfer case. I know ... this makes no sense because the only the spider gears are spinning because the front axle shift fork and transfer case are not engaged. Even the differential guy that installed the Yukon gears when I took him for a ride said the gear whine is coming from the front axle. I have a device called a mechanics ear with very sensitive wireless microphones that I plan to hook up this weekend and make sure it is coming from the front differential. The receiver has a headphone jack, so hopefully I can rig something up to record the sounds and post them on hear. More to come on this issue.
 

Budneeds2beers

Aka Mike Honcho....
Aug 25, 2016
497
2
18
Cali
Hmmm very strange. Two sets of gears installed by different techs. Sure its not a axle shaft or hub? Does your lift have the axle spacers installed? Not an alignment problem? The pinion seal that came in your rebuild kit should have grease in between the lip(inner/outer) valley of the seal. The only way to check that is by pulling the pinion.

@james correct me if I’m wrong but gear whine should be constant through the rpm gradually building and while speed increases
 
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THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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Have you tried rotating the front driveshaft while it is in 2 wheel drive? Just because the front tires are not pulling does not mean the front axle is disengaging, only thst the transfer case is disengaged. In 2 wheel drive with a functioning CAD, the front diff should barely spin if at all.

With that said, this is why I ONLY install AAM gear sets when available. AAM gear sets do not give problems if setup correctly. Yukon gears I learned do not always print correctly, and setting them up to print how you think they should will result in a noisy gear set. With Yukon gears do not try so hard to get a perfect heel to toe pattern, concern yourself with getting a good root to crown pattern with the gear lash in there specs. The last set of there gears I did went in an 8.25" ifs, but it had the np246 case, so it spins all the time. It had a horrible heel to toe pattern running the drive side about a 1/4" off the heel, but the coast side was just a hair to the toe side, BUT the root to crown pattern was beautiful. That diff runs dead quiet.
 

Lifted L5P

De Re Metallica
Mar 6, 2021
19
0
1
Montana
Hmmm very strange. Two sets of gears installed by different techs. Sure its not a axle shaft or hub? Does your lift have the axle spacers installed? Not an alignment problem? The pinion seal that came in your rebuild kit should have grease in between the lip(inner/outer) valley of the seal. The only way to check that is by pulling the pinion.

@james correct me if I’m wrong but gear whine should be constant through the rpm gradually building and while speed increases

Appreciate the response. Not sure on the axle shaft or the hub. One would not think so on a truck with only 38k miles, especially since it was totally quiet with the stock 3.73’s, but stranger things have happened like the transfer case vibration caused by an internal sprocket misalignment manufacturing / assembly error. Hopefully troubleshooting with my mechanics ear will narrow down the search this weekend. I am almost positive I saw the tech lube just about everything including the pinion seal, and it is not a squeaking sound, more of a gear whine sound, almost like it hits a harmonic frequency that peaks at 45 mph. It is one of those things I can surely live with, but it will always annoy me having a perfectionist personality disorder 🤔🤨.

I agree that one would have thought the gear whine should be a constant sound, and increase with rpm between each transmission gear change, but that is not the case.

Let you all know more details as we carefully investigate this gear whine issue.

If I have to ... will eventually drive to Everett, Washington and pay Yukon to reinstall the gears in their shop ... and hopefully disclose what the issue is.

More to come ...
 

Lifted L5P

De Re Metallica
Mar 6, 2021
19
0
1
Montana
Have you tried rotating the front driveshaft while it is in 2 wheel drive? Just because the front tires are not pulling does not mean the front axle is disengaging, only thst the transfer case is disengaged. In 2 wheel drive with a functioning CAD, the front diff should barely spin if at all.

With that said, this is why I ONLY install AAM gear sets when available. AAM gear sets do not give problems if setup correctly. Yukon gears I learned do not always print correctly, and setting them up to print how you think they should will result in a noisy gear set. With Yukon gears do not try so hard to get a perfect heel to toe pattern, concern yourself with getting a good root to crown pattern with the gear lash in there specs. The last set of there gears I did went in an 8.25" ifs, but it had the np246 case, so it spins all the time. It had a horrible heel to toe pattern running the drive side about a 1/4" off the heel, but the coast side was just a hair to the toe side, BUT the root to crown pattern was beautiful. That diff runs dead quiet.

Appreciate the response.

The front driveshaft spins freely in 2wd with the transmission in park laying under the truck in my garage. When placed in 4wd you can hear the range fork actuate, and when engaged I can no longer spin the front driveshaft.

Unfortunately AAM has decided to no longer offer an aftermarket ring & pinion gear set (front & rear) beyond the 4.10 ratio (this is an option for the gas motor HD trucks) ... likely because of low demand due to the locked ECU on these trucks, and GM no longer offering an option in the ECU for axle gear ratio changes on the L5P Duramax. I would have went with AAM if they were offered ... it was not a pricing issue, it was a non-availability issue.

I appreciate the insights regarding the print. I will pass this on to the installation technician when he pulls the diff covers for inspection in the coming weeks, just need to find a time that fits my work schedule, that way I can borrow a company truck for a couple days.

Thanks again for the insights ... will add to this post as we dig further into this gear whine issue.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
18,299
488
83
Phoenix Az
Have you tried rotating the front driveshaft while it is in 2 wheel drive? Just because the front tires are not pulling does not mean the front axle is disengaging, only thst the transfer case is disengaged. In 2 wheel drive with a functioning CAD, the front diff should barely spin if at all.

With that said, this is why I ONLY install AAM gear sets when available. AAM gear sets do not give problems if setup correctly. Yukon gears I learned do not always print correctly, and setting them up to print how you think they should will result in a noisy gear set. With Yukon gears do not try so hard to get a perfect heel to toe pattern, concern yourself with getting a good root to crown pattern with the gear lash in there specs. The last set of there gears I did went in an 8.25" ifs, but it had the np246 case, so it spins all the time. It had a horrible heel to toe pattern running the drive side about a 1/4" off the heel, but the coast side was just a hair to the toe side, BUT the root to crown pattern was beautiful. That diff runs dead quiet.

This is why I asked for pics. Like ferm said, the heel toe is of minimal concern, it’s the root, crown and feathering out to the sides that needs to be of concern. There is an art to this. US Gear is notorious for whining and I know of guys that can make them as quiet as stock gears. Them holding up to abuse is another story.

Pinion seal squeal can happen of the seal was not lubed. You build enough speed/momentum with the spider gears turning and the driveshaft starts to turn. The spider gears are not slinging oil to the pinion but it’s starting to move and can squeal some. It’s rare but it happens.

As for u-joints, working angle isn’t the same as what you are talking about. Here’s a link to find it. It can be confusing and you think you have next to no angle but you actually do

 

Ridin'GMC

I like red
May 20, 2010
597
0
16
MA
What gear oil are you using? Try changing gear oil brands any what type of weight are you running? In some cases, a lucas oil stabilizer can help with the whine. If those didn't work, then it's a gear issue. You may have to change the contact pattern a bit from the usual standard footprint pattern such as from being centered to slightly toe/heel. A slight change to the footprint can change the noise.