Need help diagnosing drivetrain noise on 2012 Yukon

[i6pwr]

This is a 2012 Yukon Denali AWD, has 122K miles. I bought it with 85K and it was well maintained, but unsure of diff fluid changes. I'm fairly certain it's the 8.6" rear.

When I bought it, I changed both diff fluids and transfer case fluid. About a couple months after the purchase, I replaced the tires, they were worn and slightly noisy.

Maybe they covered this up, but there was a very, very faint driveline noise under load above about 50 MPH

The area around the rear pinion was moist but not wet, there was light spatter on the floor pan above the pinion, but no drips.

About 6 months later I noticed about 5 drips or so per night under the rear pinion and then soon after replaced the rear pinion seal.

I have since replaced both front hub and bearings, both motor mounts, trans mount, and both front diff brackets, new U joints and both driveshafts balanced. U-joints are Spicer and pivot very freely.

I needed to replace all that anyway, but the driveline noise is definitely more isolated.

This sound has a very slight, low intensity sine wave like noise. Starts low then rises then quickly dissipates. Almost like when the ring and pinion teeth meet back up, about every 1.5 seconds at 60 MPH.

This is only under load and not coast. If the radio is on you can't hear it...you have to know it's there,

Could this be excessive backlash? If so, can that be corrected without damaging the teeth, or is this more of a pinion bearing or carrier bearing noise?

All input appreciated.

 

[Cujet]

Since it is AWD, is there some discrepancy in the tires or tire diameter? (I know you said new tires) And you are sure it is not uneven tire wear?

YouTube for examples of noisy differentials. Clearly when they are worn, they whine.

 

[Jim_Truett]

What was the condition of the fluid drained from the differentials? I have seen many failures of the front differentials in these.

 

[SatinSilver]

@clinebarger on this. If you're in the Dallas (DFW) area I'd bring it to him. One of the best troubleshooters out there.

 

[i6pwr]

is there some discrepancy in the tires or tire diameter

No, all four were bought new at the same time, Defender LTX.

What was the condition of the fluid drained from the differentials

Didn't have any shavings or bits of metal,, but had a grey tint.. but not full on silver goop that you clean off the magnet, but a light grey hue. I replaced with Amsoil Severe Gear 75-90 so next drain will tell alot as it's almost clear fluid.

If you're in the Dallas (DFW) area I'd bring it to him

No unfortunately......NoVa area.

 

[D60]

For giggles check pinion angle (although I don't know if it can be easily adjusted on the coil rears??)

No, it's not backlash. Could be pinion bearings.

You do have the rear filled to the bottom of the fill hole, yes? Ignore GM's stupid 5/8" (or whatever) below rule.

 

[i6pwr]

You do have the rear filled to the bottom of the fill hole, yes?

Yes.

I let it spill out until it stopped.

I will look into the pinion angle.

 

[Kira]

Something elsewhere?
Large axle U-bolt shifting/buzzing...broken spring...,weird harmonic effect involving worn shocks?

 

[jhellwig]

Check the rear axle bearings since you already replaced the fronts.

 

[i6pwr]

Check the rear axle bearings since you already replaced the fronts.

Now that you mention that, when I was reinstalling the driveshaft, I noticed an area around the backing plate that is "stained" but not yet "wet" with gear oil.

So I just went out and took this pic.
This is the RH side, but the LH side isn't as pronounced, but def not dry.

I wouldn't think the axle bearings could cause that noise but, maybe they can.

I was thinking about replacing them a while back but didnt want to mess with the ABS reluctor wheel as I don't have the Kent Moore tool to pull just the bearing...so I left them alone.

Might just pull both and replace the tone ring and bearing if the bearing is bad and damaging the seal.

 

[i6pwr]

Large axle U-bolt shifting/buzzing...broken spring...,weird harmonic effect involving worn shocks?

Sorry, messed up the last post, forgot to include this.


Everything else is tight, shocks and struts are new.

This definitely sounds like a rotating harmonic but can't pinpoint it.

The axle bearings are very plausible here as both seals have slight leakage..but only a stain, nothing wet.

 

[Jim_Truett]

The axle bearings are very plausible here as both seals have slight leakage..but only a stain, nothing wet.

Plausible, but not probable at your mileage, in my opinion. You could always tear it down far enough to slide the axles out a few inches and look at the wear pattern where the bearings ride. But that's a bit of work. Unfortunately the front drivetrain can't be disconnected for testing purposes.

Anyone in your area rent chassis ears?

 

[clinebarger]

The area around the rear pinion was moist but not wet, there was light spatter on the floor pan above the pinion, but no drips.

About 6 months later I noticed about 5 drips or so per night under the rear pinion and then soon after replaced the rear pinion seal.

This caught my eye, Re-Crushing a Crush Sleeve is more of an art than a science. Is there any slack in the Pinion Yoke?

You likely have a 9.5" Semi Float 14-bolt, If not.....The differential is likely not original to your truck which could throw off the Pinion Angle.

All the 5.3L GMT900 SUV's got the 8.6" 10-Bolt, While 6.2L equipped ones got the 9.5" 14-Bolt.

 

[D60]

I

This caught my eye, Re-Crushing a Crush Sleeve is more of an art than a science. Is there any slack in the Pinion Yoke?

You likely have a 9.5" Semi Float 14-bolt, If not.....The differential is likely not original to your truck which could throw off the Pinion Angle.

All the 5.3L GMT900 SUV's got the 8.6" 10-Bolt, While 6.2L equipped ones got the 9.5" 14-Bolt.

People act like reusing a crush sleeve is no big deal but I don't like doing it one bit. Without getting the carrier out of the way you're completely flying blind on pinion bearing preload.

 

[i6pwr]

While 6.2L equipped ones got the 9.5" 14-Bolt

I believe that was the RWD models. AWD gets the 8.6"

I could be wrong but that's what I remember.

 

[i6pwr]

Plausible, but not probable at your mileage, in my opinion. You could always tear it down far enough to slide the axles out a few inches and look at the wear pattern where the bearings ride. But that's a bit of work. Unfortunately the front drivetrain can't be disconnected for testing purposes.

Anyone in your area rent chassis ears?

When I changed the fluid, the teeth did look good, but that doesn't tell the whole story. When I change the bearings I'll get a better look.

I do want some chassis ears...may have to splurge..don't know anyone off hand who rents them but worth

This caught my eye, Re-Crushing a Crush Sleeve is more of an art than a science. Is there any slack in the Pinion Yoke?

When you say slack, do you mean in and out or up and down? If so, that feels fine, I did check that with the shaft removed.

The guy who changed the seal has been building rears for over 30 years...however, the part that did bother me was he didn't pull the brakes and use a torque wrench to determine rotating torque. He was very confident it would be fine.

It definitely is an art to get it right, and that's why I didn't want to mess with it, but I would have surely used a torque wrench to double check.

This still could be the root cause but I don't recall if the noise was there before or not.

I

People act like reusing a crush sleeve is no big deal but I don't like doing it one bit. Without getting the carrier out of the way you're completely flying blind on pinion bearing preload.

I agree.

If I get to changing the bearings and seals soon, I will pull the driveshaft and check the rotating torque.

 

[D60]

I still don't understand how anyone thinks you'll get an accurate preload reading with the ring gear and carrier in there, but do what you will.

That said, if it was done by someone with experience, you don't have any pinion play, and the seal is not presently leaking, then this is probably not your problem.

I'm still curious about angles -- if for no other reason than it's free and easy to check. If u-joints are external clips you may want/need to pull a clip to set a socket in there to "extend" that plane for an angle measurement, but that's 10 seconds. Everyone has their own method but I prefer to measure directly off the caps as the yoke castings are not precision and often taper anyhow.

 

[i6pwr]

I still don't understand how anyone thinks you'll get an accurate preload reading with the ring gear and carrier in there, but do what you will

I see what you're saying. I thought there was also a way to determine the correct rotating force for just the ring and pinion together...but maybe not.

I will also look into getting the pinion angle, will be a few days as we are with relatives this week.

 

[D60]

I see what you're saying. I thought there was also a way to determine the correct rotating force for just the ring and pinion together...but maybe not.

Some claim you can account for it.

 

[PontiacHO]

This caught my eye, Re-Crushing a Crush Sleeve is more of an art than a science. Is there any slack in the Pinion Yoke?

You likely have a 9.5" Semi Float 14-bolt, If not.....The differential is likely not original to your truck which could throw off the Pinion Angle.

All the 5.3L GMT900 SUV's got the 8.6" 10-Bolt, While 6.2L equipped ones got the 9.5" 14-Bolt.

These later rear axles are even more challenging because the pinion nuts are staked. The last ones I did I replaced the pinion nuts with new. Sounds stupid but I also measured the amount of pinion threads protruding out beyond the pinion nut before removing. I felt like that may be a good reference for how far to run the new nut back down. Of course stopping and checking the slack/feel all the way. Too loose is probably worse since that will definitely eat the ring and pinion gear surfaces…