Help request in identifying the Differential in my Envoy?

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
Hi, I was wondering if anyone can help me identify the type / model of rear differential is in my '06 Envoy SLT? Looking at Diff covers and gaskets etc.. and there are multiple for this vehicle. Would it be on the RPO sticker I think in the glove box? Thanks in advance!
 

Beacon

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Mar 22, 2019
445
SouthWestern PA
Yes that info is in the glove box
 

Reprise

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That will give you the axle ratio (GU6 = 3.42, GT4 = 3.73; those are the usual two).

If you can't tell from the shape of the cover, there will probably be a 7- or 8-digit part number cast in the housing (I forget whether it's on the driver's or passenger's side; I saw it recently and think it's on the pass. side) That part # in google will give the housing type.

Mine is an 8.6"; GM put those in a ton of vehicles (cars *and* trucks / SUVs), but a lot of the 6cyl 360s got a different housing (I forget as I write this on my phone). But I remember it has a prominent bulge on the cover to accommodate the ring gear - almost diamond-shaped, IIRC).

If you still can't determine, snap a pic, and someone will reply back, I'm sure. Guessing you want to know in order to get a new cover gasket.
 
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jmonica

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Apr 2, 2013
384
Hamburg, NJ
Thanks for the reply. I am going t snap a pic right now. I appreciate your help man! I am about to pull everything apart and do some rust proofing and just clean it all up so seems like the perfect time to change the rear end fluid. Sorry, probably TMI... Thanks again!
 

jmonica

Original poster
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Apr 2, 2013
384
Hamburg, NJ
Ugh this is embarrassing. I don't even want to post this pic. Just to give a little be a context to teh condition of this vehicle. I live in the northeast. The last time I drove it, the transmission lines leaked on the highway, so the trans lost 2-3rd gear. It sat for almost two years before I just recent;y fixed it. And this is now what the underside of it looks like. I've done the rust removal on the vehicle from the transfer case forward. This is what the rear of the vehicle looks like. BUT not for long! I won't even drive this thing looking like this. I knew it was bad but this is ridiculous. smh... Anyway I hope this pic will help Identify the differential. I'm fairly sure i can figure out what gasket I need but any input would be most welcome. Thank You!Envoy DIff.jpg

That will give you the axle ratio (GU6 = 3.42, GT4 = 3.73; those are the usual two).

If you can't tell from the shape of the cover, there will probably be a 7- or 8-digit part number cast in the housing (I forget whether it's on the driver's or passenger's side; I saw it recently and think it's on the pass. side) That part # in google will give the housing type.

Mine is an 8.6"; GM put those in a ton of vehicles (cars *and* trucks / SUVs), but a lot of the 6cyl 360s got a different housing (I forget as I write this on my phone). But I remember it has a prominent bulge on the cover to accommodate the ring gear - almost diamond-shaped, IIRC).

If you still can't determine, snap a pic, and someone will reply back, I'm sure. Guessing you want to know in order to get a new cover gasket.
HI. Does the pic I posted help? If not I will drop the spare tire and take a better one. Thanks mate!
 
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Reprise

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Kind of hard to tell from the pic, but that appears to be the 8" cover.
Bottom (& top) come to a slight point / taper, the 'hump' is more or less a squared-off oval, and the d/s part of the hump is just slightly raised higher than the p/s.

It would be good for you to check out some replacement covers online, to match up & verify what I stated above.

Rock has pics on their site, which is where I looked.
 
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jmonica

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Apr 2, 2013
384
Hamburg, NJ
Ok Thanks. I am definitely going to replace the cover and bolts as I tear everything apart and restore all of the parts or replace them if i have to. If I can find a part number on it, that should help? At least I know it's a 10 bolt so I know how many new bolts to buy! :smile: Thanks again.
 

Reprise

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You likely won't find the part # on the cover (that would be too easy, plus yours has some good rust on it). Rather, it will be on the case, or perhaps the axle tube.

Good luck!
 
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Maverick6587

Member
Dec 16, 2018
730
Sterling Heights, Michigan
It should be on your RPO sticker, post a pic (leaving the VIN out of the pic, if you are concerned about that for any reason) of it if you're unsure. You probably have the G80 axle.

@jmonica What are your plans for rust removal or what have you done to the front side? I've been working on rust removal on mine and a grinder with a wire wheel seems to be most effective and quick. It doesn't really get to all of the rust corners though.

I think I'm going to do round 2 this spring/summer and use either loctite (it is in gel form). The gel will be nice for those tight corners.
 
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jmonica

Original poster
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Apr 2, 2013
384
Hamburg, NJ
It should be on your RPO sticker, post a pic (leaving the VIN out of the pic, if you are concerned about that for any reason) of it if you're unsure. You probably have the G80 axle.

@jmonica What are your plans for rust removal or what have you done to the front side? I've been working on rust removal on mine and a grinder with a wire wheel seems to be most effective and quick. It doesn't really get to all of the rust corners though.

I think I'm going to do round 2 this spring/summer and use either loctite (it is in gel form). The gel will be nice for those tight corners.
Hey Maverick,
I wasn't even planning on doing any rust removal when I started the trans swap. I had parked it the day the trans went out and that was during a bad snow storm and I think that was a bad move because,, well you can see the rust I have. Once I took the wheels off and saw what was there, I got sick looking at it.
I swear by evaporust. For some of the larger parts like the drive shafts I went to a plumbing place and bought some 4 or 5" PVC and 2 end caps. I let the driveshafts soak in those for a few days. it really did a god job on them (see pics). Of course when I was removing them, I dropped the tube the bottom cracked and I had a sea of evaporust on my garage floor. hehe What a mess. All of my tools where still on the floor from doing the trans etc.

For things like the the steering knuckles, I just hit them with the wire brush on a drill and then sprayed them with some VHT Epoxy paint before replacing the ball joints. You can make a shower/bath for large parts if you use a pump and let the evaoprust just run over the part and just let it keep recirculating. I bought a aquarium pump and it just didn't work out so I scratched that idea.
Some of the things under the vehicle, I used that Rustoleum rust reformer stuff that turns the rust into some unknown elimiment and then coated that with the VHT epoxy. The VHT Rust convertor didn't seem to work very well for me. Who knows how long that stuff will last but it's supposed to be rust, salt etc resistant. I'll just have to keep on eye on it I guess.

I've only done the front and still have the drivers side controls arms etc to do. I am rebuilding the calipers and will tackle that side when I do the brakes. Oh for some of the really bad parts, I made myself a blast cabinet and use media to blast those parts. Especially if I soaked them and the rust didn't come off. Yes I know it's kind of hokey but it works man (see pics). I blasted then polished and nickel plated the calipers on my other vehicle and they came out looking good. I was going to do that on the Envoy but there's only so much time and grinding and sanding the calipers was like 10 hours ordeal for each caliper.

Oh I also nickel plated some of the brackets and nuts etc in the engine bay. That's a separate project I am going to start after I get the rear of the car done. The only reason I am plating those parts is because I bought the plating kit a long time ago for another project and it has a limited shelf life so I needed to use it. Plus I'm divorced, only have my son 50% of the time and have no life so there you go.

I also replaced the trans cooler lines and am going to do possibly the PS lines in steel braided. I just 3D printed some clamps to replace the stock metal brackets.

So do you have any tips on rust removal? I am all ears man.

I still have the entire back half left to do so any tips will be most welcome! Gonna pull the sway bar and repaint it etc and probably just go flat black epoxy stuff for everything else. I mean even the shocks (Rancho) are rusted. It's depressing when I get under there and look at it. If I only had a lift in my tiny garage! Or bigger garage!

BTW.. Thanks again for any help you provided during the trans swap. I really appreciate it. will post the RPO as soon as I get home and get a pic of it. Thank You
IMG_8305.jpgIMG_8435.jpgIMG_8407.JPGimage0.jpegIMG_8077.jpg
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
It should be on your RPO sticker, post a pic (leaving the VIN out of the pic, if you are concerned about that for any reason) of it if you're unsure. You probably have the G80 axle.

@jmonica What are your plans for rust removal or what have you done to the front side? I've been working on rust removal on mine and a grinder with a wire wheel seems to be most effective and quick. It doesn't really get to all of the rust corners though.

I think I'm going to do round 2 this spring/summer and use either loctite (it is in gel form). The gel will be nice for those tight corners.
Hey Maverick. Hope you're having a nice weekend so far. Below is a pic of my RPO sticker and VIN. Can you possibly tell me which numbers I am looking for to ID my differential? I'm not sure what to do with this now that I have a pic of it? Thanks man!

RPO.jpg
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
Yes that info is in the glove box
Thank YOu for posting this. It helped me immensely!
 
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jmonica

Original poster
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Apr 2, 2013
384
Hamburg, NJ
Please ignore my request for help. I don't know how I missed Beacons post but I'm a dumb a$$. I see now that I have a GU6 thanks to his post. Thank You everyone who helped!
 
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jmonica

Original poster
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Apr 2, 2013
384
Hamburg, NJ
And of course, my Envoy has the oddball, black sheep crappy A$$ 8" rear. There are literally hundreds of different diff covers for the 8.5" 10 bolt, and there's literally one for the 8" 10 bolt. Most 10 bolt identification websites don't even mention the 8". Why would mine have the better/bigger, more common rear end, much less a posi rear? That would make my life just a little bit easier and lord knows this vehicle will never let that happen. It fights me on every single thing I try to do to it. smh... and so endeth my rant.
 

TollKeeper

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Dec 3, 2011
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Brighton, CO
But a swap over to the larger diff is a straight swap. So its not the end of the world. My envoy has the larger diff but GU6. Other than i wish it had more balls pulling a trailer, i like it. 2nd winds out at 85 mph, she got legs!
 
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jmonica

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Apr 2, 2013
384
Hamburg, NJ
I hear ya. I know it's not the end of the world. I really was kind of surprised and disappointed to discover that I had the 8" diff, but its no biggie. I don't tow anything so whats the difference really, other than I can't finds a nice differential cover for it. Again, who really cares? I'm doing a semi-restoration on mine and I think I'm just burning out at this point. Thanks
 

Maverick6587

Member
Dec 16, 2018
730
Sterling Heights, Michigan
I hear ya on the getting tired on the restoration! I thought I was going to have a nice little brake since my 06 was running perfectly. I got the 07 and now I'm starting from scratch on repairs all over again. :bonk:

On the rear end side of things... I think I'm going to convert at least the 06 to a Strange Engineering S60 (Dana 60). If you're looking to swap/change your differential, Strange is the best IMO. :2thumbsup:
 
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jmonica

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Apr 2, 2013
384
Hamburg, NJ
OK good to know. I"m going to check them out for sure. Thanks! Adding to my feelings of burnout on the envoy is the fact that I have another car, my DD, that I have a bunch of new parts for, including a nitrous setup, just calling my name. I have all new Hertz speakers that I got back in October as a birthday gift, just sitting on top of the toolbox while three of the four in my car are blown so bad that I have to listen to sound coming from one single coax from the back of the car. U have a list of things as long as my arm that I want to do to it but the envoy "Trans swap" is just dragging on forever. The trans is done. It's all of the other crap that I discovered that needed to be fixed while doing he trans. I had been working 7 days a week since Sept though and now I'm back down to 5 [daw] so now I should finally be able to wrap it up in 2 more weekends. Famous last words. I find I have to at least double my estimated time to fix a problem on the Envoy. The plan is to finish the envoy first or I'm afraid I won't get back to it.
 
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Beacon

Member
Mar 22, 2019
445
SouthWestern PA
I can't believe that the 8" rear diff gasket is between $35-$40+ and the 8.5" is only about $7. smh...
I've heard from multiple sources, that you don't have to replace that gasket with a new one, that the old one can be re-used without issues. Or you could use permatex, just make sure it is compatible with gear oil. That being said, I bought a new gasket when i did mine. But I think it was $28 from napa.
 
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jmonica

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Apr 2, 2013
384
Hamburg, NJ
I've heard from multiple sources, that you don't have to replace that gasket with a new one, that the old one can be re-used without issues. Or you could use permatex, just make sure it is compatible with gear oil. That being said, I bought a new gasket when i did mine. But I think it was $28 from napa.
Really? That's interesting Thank You. I wonder of that's why its so expensive (for what it is I think.). My diff cover and bolts are so rusted that I will probably just buy the new cover/gasket and bolt set from Rock Auto for $29. I promise I'm not cheap, but the shipping charges at RA often kill the deal for me unless I am ordering a bunch of stuff and can get them from the same region (A,B or C). Sigh... I just wanted to run out today pickup the gasket, media blast the cover and get some new bolts and be done with it today, but can't find it in stock locally and the gasket only price is too much anyway. BUT if I could reuse the existing one, I could go tear it apart right now, blast the cover and be done. I need to be able to pull the vehicle out of the garage today though so I'm not sure if i should rely on the fact that the gasket will definitely still be usable. I can't just ush it out either due to the slope of our driveway and lack of help. I guess I could just use some permatex temporarily to get it out of the garage if it came to that.

I usually plan ahead and if this was a 8.5" diff I wouldn't need to., I can pickup a gasket for one of those at the 7/11 (Just kidding but almost...). Crap what to do...... Thanks again!
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
I never use a gasket. Its what they make RTV for. I change my fluids far too often to mess with a gasket. Never have leaking issues.
 
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jmonica

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Apr 2, 2013
384
Hamburg, NJ
I never use a gasket. Its what they make RTV for. I change my fluids far too often to mess with a gasket. Never have leaking issues.
OK cool thanks. More research and the consensus seems to be with you so I am skipping the gasket. I bought the Permatex made for diffs in the green packaging so I think that I am good to go. Appreciate you posting!
 
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jmonica

Original poster
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Apr 2, 2013
384
Hamburg, NJ
I never use a gasket. Its what they make RTV for. I change my fluids far too often to mess with a gasket. Never have leaking issues.
Just to report back. I followed your advice and just used RTV to seal the diff cover and so far so good. After a few hundred miles, not a drip (from the differential)! I appreciate your help!
 

Sparky

Member
Dec 4, 2011
12,927
Just as a note (not sure if anyone mentioned it and I just missed it) but the 8" rear is not that "oddball" for the platform. The GU6 8" is the most common axle on the GMT360 as that is what was primarily paired with the 4.2L on the short wheel base. Only EXT or V8 got the 8.6" and even then the pumpkin is not the standard 8.6" pumpkin so those covers you see won't fit anyway (thankfully the guts inside of the 8.6" pumpkin do match everything else 8.6").

Another platform oddity :dunce:
 

iawegian

Member
Jan 3, 2021
1
FairPlay Colorado
Thank you all for the info.
The front Diff in My 06 XL Denali ate her pigs when I was heading south on I-25 out of Denver. Fortunately Traffic was light and I made it to an exit Trailered it back to Fairplay and about to disassemble. I’m sure I’ll find debris all over the inside when I get it out.
At 13” shorter overall, and only 1” lesson wheelbase than a Suburban, I’ve found this to be one of the best towing vehicles ever. So I want to keep her if she’d loosen up and run again.
Robert
 

TollKeeper

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Dec 3, 2011
8,047
Brighton, CO
You could always just pull the half shafts, and the drive axle to get thru the summer, or until you find the parts.
 
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jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
Dang it, I only ever posted a “before” pic of the rear end of the truck? What good is that? It’s not a Jenny Craig ad with just the fat version of someone.
Here’s a pic after dust removal and a quick rattle canning of whatever paint I had on the shelf. It was either that black, Orange parking lot paint or high gloss white. I’m confident I made the right choice.
Skip ahead 5 minutes.... Now I see why I didn’t post an after photo. The only one I have has the diff cover installed with painted over bolts. I replaced those for stainless bolts. Yea I have no life obviously.
1620848389573.jpeg
 

jmonica

Original poster
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Apr 2, 2013
384
Hamburg, NJ
hehe That is odd. I can assure you that it has al 10 bolts now, I wonder what made me take that pic before I had all 10 in? Weird man. Thanks!
 
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