So, did I dodge a bullet? (front diff)

[Reprise]

Took the Voy into the city a little while back, and on the way home, started hearing a noise similar to when one has air in their heater core (best way I could describe it). However, the noise was from the *left* front wheel area (and only happened 'in motion'.

Had to drive it about 60 miles home at highway speeds, noise all the way. But got it home without incident, and parked it.

Put it in the garage & started taking things apart. By this time, I'm suspecting wheel bearing, perhaps?
Events:
Left wheel off ground, rotate wheel. No noise.
Removed wheel, checked brake / rotor. Fine.
Removed caliper / rotor / hub. Saw this hub was practically new (maybe 10K miles on it). No noise, spun fine.

Checked front diff fluid level, using the old 'ziptie as dipstick' method. *Dry as a bone*.
Removed drain plug for diff. About six (!) drops came out - slowly. At this point, I know my 'oil leak' I'd been ignoring forever... was gear oil, from the diff. Suspect the Envoy is going to get a 4WD > 2WD conversion (I never use 4WD).

Turn the driver side CV axle - no noise, binding (and boots were fine).

Removed the axle and examined it and the innards of the diff on the driver's side...
- No real scoring on the CV axle (the pics will show a dark band toward the edge, which has just a small ridge I can feel
- Diff outer seal originally looked intact, but as I look at the higher resolution pics on the laptop, I see it's compromised at the top. From what I can tell, the fluid didn't leak out from there (at least, on an ongoing basis)
- Outer bearing race looked / felt ok (no scoring, binding, bearing race and bearings rotated freely. However, I did detect about 1/8" to 1/4" of play inward / outward. *No unusual noise*.

Pics are below. I see three options...

- Reattach CV axle (after replacing seal), fill with fluid, and 'send it', until spring. I was planning on using the Envoy a bit, but don't have to. However, when I was going to use it was going to be when the roads were snowy, etc.
No further noise = good to go until warmer weather and I can rebuild (or replace) front diff.

- Remove other CV axle and front driveshaft, and implement 'Gatorade cap fix' on both diff openings (again, until spring... or maybe forever?)

- Bite the bullet (that almost hit me?), and rip out the front diff / rebuild (or replace) now, along with at least one new CV axle.
I don't like this option because it kills my winter plans for the Sierra, but I'd do it if it's the best option (prevent more parts from failing, etc.) I do know this is a LOT of work (and I have the V8, so room is always at a premium. Again... if I use 4WD more than 2 days a year, that's a lot. And I know I'll need to service the front disconnect, etc., etc.


And without further ado... pics for review... The CV axle appears OEM, based on the yellow paint on the inner shaft side... (360" view)









And the diff opening - driver's side...

 

[flyboy2610]

I would go with option 1. Replace the seal, fill it with 75W-90 gear oil (don't ya just LOVE that smell?) and drive it when needed.
Rebuild or replace (if needed) when the weather is warmer.

 

[kborro01]

Just replaced my front diff on my 03 Envoy. What a PIA!! Knew I needed a new one so I picked one up from the junk yard, pulled it apart, checked the bearings, replaced all 3 seals. Taking the old on off and installing the rebuilt one was a 3 day job by myself. But no issues. So I know this wasn't one of your options, but it is an option, plus you can rebuild the one currently on the vehicle and have a spare.

 

[Mooseman]

I'd fill it and see if it still makes the noise. If it doesn't, replace the seals and call it a day. You may have just dodged the bullet and the diff may be fine. If it does fail later, yank the axles and driveshaft until able to fix or replace.

BTW, when I parted the Saab, yanking the front diff was actually not that bad from the top. Was actually surprised. Remove the fan, shroud, PS pump and anything else that's in the way on that side. Did have to twist and turn it. Mind you, I was treating the old girl like a discarded pick and pull yard 'ho. Can't remember if pulling the water pump made a difference but I doubt it.

 

[Reprise]

I've been also looking at rebuild kits, as well as replacement JY units on Car-Part

JY units look to run about $250 There's one just a few miles away from me (w/ the correct 3.73 gear)

A rebuild kit runs about the same (but Yukon disco'd them awhile back; Amzn has some old stock)

Rock still has most of the seals, bearings, etc., as well as the CV axles.

From what I can see, I did dodge a bullet, IMO. I'm going to try reassembly of existing, in the short-term. Looks like no one distributes a case gasket for the AAM 7.2; Yukon's kit provides a tube of silicone in lieu of a gasket. In the spring, I'll crack the case of the old (or JY one, if I replace it) and see how making a gasket holds up. Until then, it can drip, if it goes back together without noise.

 

[littleblazer]

Wasn't aware the 7.2 used a gasket. The full sized ones are just sealed at the joint... at least the one in the 03 was. If it's like that one... the rebuild is annoying. There are no shims but rather adjusters to set bearing preload and backlash and such... yanking and installing a 12 bolt as well as rebuilding it was easier than trying to set up that damn 8.5. But so far so good.

 

[Mooseman]

There is that issue with these front diffs, they're a bitch to work on as @littleblazer explained. If it is pooched, I'd just go with a JY unit.

Spoiler: "Evil mod bug awakens"

Now this might be a good time to swap to a 4.10 gear . Gear sets for the rear are available.

 

[Reprise]

So, after getting back to this, I can say... the noise is gone.
(Or... I never had a noise from the diff. More on this in a bit)

Lesson #1: Pictures (and old eyes) can be deceiving...
After doing some extensive research for the correct seal, I went back out and cleaned up the existing seal / area.
Turned out that the seal *was* intact, after all. Here's proof...



(btw, the GM # for this seal is 12471617; National #: 710688)

I cleaned up the shaft / spline area that goes inside the diff, as well as put a little red bearing grease on it. As with my first Sierra (that also had 4WD), I found that if I finagled the axle a little bit, it will slide right in. No need to pound it in at all. Once it's in, give a good pull on it to ensure the axle has re-engaged the locking clip (see previous post for pic of the clip)

Also note: It's not too hard to get the axle out / back in. You'll need to remove the pinch bolt that holds the upper ball joint to the A-arm. Once it swings out, use your pry bar and hammer to drive out the axle at the rear. You'll need to compress the outer boot a bit against the knuckle surface, but once the inner end of the axle is out of the diff housing, simply move it down and to the side of the diff, then maneuver the axle backward, out of the hole in the knuckle, and out. Reverse for installation.

I noted that my A-arm bushings were groaning when I moved the arm in either direction -- so I know I'll either be installing a new arm or new bushings, come springtime. I have a 'full' 22pc (?) ball joint press kit now, so I'll try and save a few bucks and do a bushing replacement, when the time comes. The arm has a bunch of rust on it, so I'll grind that off and see what the arm looks like, first.

Back to our diff...
GM calls for 75W-90 Synthetic gear oil (it's an open diff, so no limited slip additive is called for (although if your oil of choice has it, it's not going to harm anything).
Since this is a temporary 'fix', I got a quart of the cheapest (non-synth) oil I could find, figuring that it wasn't going to be in the diff very long (and certainly wasn't going to see anything resembling 'severe' duty, in the meantime). STP at AutoZone, for those wondering. Cheaper than SuperTech, even (not that I'd ever use any SuperTech fluid, of any type, TBH).

Lesson #2: Doublecheck data.
I had glanced at the fill spec for the front diff. Saw an amount of ".88" something, and thought, "great... 1 qt needed". After I got the whole quart in, and seeing nothing come dripping out of the fill hole, I found out that the correct spec is about 1.3 qt.
Given that I was riding around for an indeterminant time with *no* oil in the diff... and that it would leak out like the prior fill... I didn't worry about the missing 0.3 qt. "Send it!"

Glancing at the axle / seal, there was nothing leaking from there. The groove on the polished end of the shaft can contribute to leaks (new axles should be smooth and uniform across this surface.)
Again, I'm not going to worry about it, seeing that it wasn't leaking (I'll check again later).

Buttoned everything up, and took her on the test drive...
I still had a noise from my dash area, but otherwise, everything was quiet. Rolled down the window, and everything sounded good. Drove on an errand for almost an hour... all was well.
When I got home, I decided to see if I could switch to 4WD in the driveway (shifted into neutral, first.)
Unfortunately, I got a flashing mode indicator and a lit 'Service 4WD' light on the dash. However... the encoder / mode switch had been acting a little flaky, beforehand, so I *don't* think the lack of fluid caused it to fail switching modes. Popped it back to 2 High, and the selector reported back OK (still had the dash light).

Shut the truck off, restarted it, and the 'Service 4WD' light was gone (I expected this, too). Tried to engage 4 High again, and this time, the selector lamp moved there right away. Put the truck in gear, and it seemed to be in 4WD, but I didn't have room in the drive to really check for crow hop, etc. Decided not to chance 4 Low, and put the selector back into 2 High, which is where it sits 99% of the time, anyway. Again, no issue.

So... at this point... no noise, no leaks... I'm calling it 'good enough', for the short-term. Will check again tomorrow for leakage (at the seal), but I don't expect to see any.

I still have the dash noise, at the far LH side. It's definitely from inside, not anything outside (inner fender liner, nothing mechanical). It'll be fun tracking that down (and I definitely want to, as it's a bit annoying, especially with the radio off.)
But, as I drove the truck on the errand / test drive tonight, I thought to myself... "Damn, I love this truck". It's just a shame that she gets driven the least, these days. Worse, seeing the rust all over the undercarriage just makes me really sad. The body is in very good shape, and except for the diff, she's in great shape mechanically. With only 160K or so on the clock, there's a lot of life left in her, if I can address the undercarriage. And after seeing that post a few weeks ago, where the poster took pics of his rust removal efforts... I may be able to do the same thing. Was going to preserve the Sierra's frame / undercarriage first, but it's in much better shape. So maybe I'll do the Envoy, before things get much worse. Again, spring.

 

[NJTB]

Try a place that does NIH oil undercoating. Had my frame done last year, took care of all the rust and so far is holding up nicely.
They needlescaled the frame, did a rust conversion, then undercoated. The rust conversion was a bit expensive, but I'm keeping the car.

 

[Mooseman]

But, as I drove the truck on the errand / test drive tonight, I thought to myself... "Damn, I love this truck". It's just a shame that she gets driven the least, these days.

I know what you mean. Same thing with the TB ever since I got the new Sierra. So much so that the battery died a slow death being parked and now will put on a battery maintainer and Bluetooth monitor. When I last drove it, I thought to myself "Man is this thing zippy and doesn't steer like a bus". I thing I'm gonna try to use it more often, especially for short trips since it's not good to do that to a diesel.

Just keep an eye on leakage on that seal because it's leaking from somewhere. You could add a little Blue Devil stop leak. I used that in the Avy's front diff and in the TB's power steering and did stop or slow the leaks down.

Did you check your transfer case's smurf blood? Could be why it had a hard time shifting the first time.

 

[littleblazer]

I know what you mean. Same thing with the TB ever since I got the new Sierra. So much so that the battery died a slow death being parked and now will put on a battery maintainer and Bluetooth monitor. When I last drove it, I thought to myself "Man is this thing zippy and doesn't steer like a bus". I thing I'm gonna try to use it more often, especially for short trips since it's not good to do that to a diesel.

Just keep an eye on leakage on that seal because it's leaking from somewhere. You could add a little Blue Devil stop leak. I used that in the Avy's front diff and in the TB's power steering and did stop or slow the leaks down.

Did you check your transfer case's smurf blood? Could be why it had a hard time shifting the first time.

The 07 2500 turns a tighter circle than my colorado. The TB and escalade are like driving compacts compared to those. I actually forget how good the turn in was.

But I didn't say the TB was zippy... I said God damn this thing has no balls left. I went to pass someone on the highway and matted it... probably a good 7 seconds to the floor... it went from 68 to 79... made a whole lot of noise though. It's a combination of the trans and engine just being worn I think. They took one hell of a beating.

 

[Reprise]

Some residual housekeeping... 🧹🧹

Can't remember if pulling the water pump made a difference but I doubt it.

BTW, the diff told me to tell you... "I live... I die... I live again!"

Now this might be a good time to swap to a 4.10 gear . Gear sets for the rear are available.

If I still towed with this thing, and was going to 2WD... maybe. If anything, I'd be looking to go the *other* way, with this rig!

I thing I'm gonna try to use it more often, especially for short trips since it's not good to do that to a diesel.

Yep yep! Let the gasser be the sacrificial anode!

Just keep an eye on leakage on that seal because it's leaking from somewhere. You could add a little Blue Devil stop leak. I used that in the Avy's front diff and in the TB's power steering and did stop or slow the leaks down.

Did you check your transfer case's smurf blood? Could be why it had a hard time shifting the first time.

The t-case itself is dry. And I had replaced the fluid myself, so I know it's OK. I'm figuring encoder, selector knob, or the disconnect. I did see the voltage drop when I commanded the 4WD, as I had the headlamps on. So I know the encoder was 'trying', at least. And no noise, so I'm guessing the disconnect wasn't seized. We'll see, come the warmer weather. The Sierra is headed back to my garage, shortly, for its winter project list.