Swap diff carrier from a G86 to a G80?

Mooseman

Original poster
Moderator
Dec 4, 2011
25,262
Ottawa, ON
My G86 positraction rear differential just blew out. All I hear is grinding and had to drive it home using front drive (on an AWD, it wasn't easy!). I have a spare G80 carrier. If my ring and pinion gear are OK and it's just the carrier itself (i.e. the spider gears) , can I use the G80 in the G86 differential?

I still haven't opened up the diff to see the damage. Tomorrow should be a little less cold. Just trying to look at my options. This Saab has the 3.73 gears. I can't even swap the diff from my old TB since it has 3.42 so I hope I can fix this one.
 

marinegrunt

Member
Oct 13, 2012
110
I had the G80 in my Sierra and the spider gears failed last year. I wanna say the locking mechanism was messed up too. I ended up replacing it with a Truetrac. The two carrier assemblies looked similar on the outside. I can't say for sure but I would think you'd be able to swap the two. Maybe do a side by side and compare the two.

If you need anything out of my old G80 you're more than welcome to any of it. Sounds like you have a good G80 though.

I know a mechanic that specializes this kind of stuff. I'll try and get a hold of him and see what he says.
 
  • Like
Reactions: Mooseman

Mooseman

Original poster
Moderator
Dec 4, 2011
25,262
Ottawa, ON
I've seen that on Youtube regarding the spider gears in open diffs but this one is a posi and they are quite a bit more expensive, which is why I'm looking at swapping in the spare G80 instead.

Thanks for the offer but I should be good and shipping to Canada would be expensive. If you do hear anything from your friend, please let me know. I just hope that I don't have to re-adjust anything like pinion depth and backlash since I'm not equipped for that sort of stuff.
 

Mooseman

Original poster
Moderator
Dec 4, 2011
25,262
Ottawa, ON
Well, this sucks!

20150109_161533_resized.jpg

20150109_160756_resized.jpg


Looks like the lock pin got loose, came out and allowed the pinion pin to come out. You see it sheared in half. The caps in the diff look like they were taken out before because they have crude punch marks to identify them. Ring and pinion look OK. So looks like I'll be swapping in the G80 but I'm being delayed by something else. I have to replace the bearings on it since I don't have the original races.

The previous owner of this truck was an idiot if he didn't properly torque the locking pin. I'm just hoping it will be a straight swap without having to do adjustments.
 

Mooseman

Original poster
Moderator
Dec 4, 2011
25,262
Ottawa, ON
I just hope I don't lose a a finger or two in the process. I'll update on my progress.
 
  • Like
Reactions: Mounce

marinegrunt

Member
Oct 13, 2012
110
Wow...what a mess.

I haven't heard back from my buddy yet on whether or not he knows if the 86 and 80 carrier are interchangeable. I'll let you know as soon as I find anything out.

One thing you might want to do is to try and find the exact oem carrier bearings in hopes that you won't have to make any adjustments to the backlash. You know how aftermarket parts can be sometimes. I know you said you aren't setup right now to make any adjustments, but at the very least, I'd use some gear marking compound. Also be sure you preload the bearings. If the carrier bearing preload is off it'll either toast the bearings or they will be loose causing your backlash to change. With a different carrier being installed you might have to make some adjustments anyways but you may get lucky. Gear pattern should let you know or at least get you close. If not, you really only need a range dial indicator to get it setup where it needs to be. Even with a range dial indicator, your final check is with the gear marking compound. If your gear pattern is good then you should be good to go. Be sure to check the drive and coast pattern. This may be stuff you already know or have thought of but thought I'd mention it just in case. I'm nowhere near an expert on all of this. I've only setup 3-4 diffs in the past but might be able to help a little if you need it.

I was thinking....we have an Envoy with the G80 and the 3.73 ratio. I wonder if you searched for say a Truetrac for your Saab and then did the same search for our Envoy. If the part number off of the two TrueTracs match up that should mean they're interchangeable, correct?

What is the G80 out of? If you have the whole rear end you could just swap out the whole thing so you don't have to worry about making any adjustments. It shouldn't take as long either.

Good luck with it all. I'm sure you'll have it up and running in no time.
 

Mooseman

Original poster
Moderator
Dec 4, 2011
25,262
Ottawa, ON
Yeah, I've been reading online and checked AllData. So far says that if I am just replacing the carrier, I might not need to readjust anything but to check the pattern just in case. I don't think that a different bearing manufacturer will have measurable differences in specs if it's a reputable manufacturer.

I got that carrier from a junker at the local u-pull yard as a spare because I had heard of so many G80's blowing up. I know it's from an EXT/XL so it's for the 8.6" R&P. The only thing different so far with the case is the missing drain plug.

And of course this has to happen in the dead of winter and where I have two other things on the go :mad: .
 

marinegrunt

Member
Oct 13, 2012
110
Isn't it crazy how stuff like this always seems to happen at the worst possible time. It never fails.

Our Envoy is the XL and also doesn't have the drain plug. I had thought about putting one in but figured it's a good idea to take a look inside when the fluid is due to be changed. It also gives a chance to clean off the magnet.

I also read that when I installed the Truetrac in my Sierra after my G80 failed that I wouldn't have to make any adjustments but I did end up having to. You would think that if the two carriers are the same the 80 would be in the exact same spot as long as you use the original shims.

Here are a few links to some websites I look at when doing rear ends. They have some great info with step by step instructions.

www.pirate4x4.com/tech/billavista/Gear_Setup/

http://www.truckmodcentral.com/forums/f168/gm-10-bolt-rear-gear-install-setup-11732/
 

Mooseman

Original poster
Moderator
Dec 4, 2011
25,262
Ottawa, ON
That's some good info right there. Thanks MG!
 

Mooseman

Original poster
Moderator
Dec 4, 2011
25,262
Ottawa, ON
Just an update.

The G80 does in fact swap into a G86 diff. Fits the same as the original G86. But, in my case, something else is borked because the ring and pinion binds in three spots, making me think the pinion bent.

Instead of dicking around setting up a new ring and pinion, I'm just going to swap out the whole diff. Problem will be finding one from an EXT/XL (for the 8.6") with 3.73 gears since the majority have 3.42.
 

marinegrunt

Member
Oct 13, 2012
110
Sorry to hear that Moose. That really sucks.

That's good info about the cases just in case anyone else is ever in the same position. I never did hear back from my buddy. He may not have known for sure anyways.

Seems logical that the pinion is bent if it's binding in 3 spots and especially considering the other damage the diff had.

I bet pinion depth would be pretty darn close if you installed the ring and pinion from the G80 as long as you used the inner and outer pinion shims from the G86 housing. When I set my pinion depth all I went by was gear pattern. I didn't have the special tool it called for and most don't use it anyways. That tool is just to get you in the ballpark. It might be worth at least tossing it in. I think you'd be surprised just how close the gear pattern will be. I can't remember the cost but I got the new crush sleeve from the dealership and they had it in stock. I want to say it was like $12. That should be all you need to make the swap. If the pinion is bent I wonder if it could have damaged the bearing too? I realize all of this takes time though and that might be something you just don't have right now.

I found this listing on ebay. I realize it's not the right rear end, but they sure do seem to have a bunch, plus they're located in Canada. It might be worth giving them a call to see what they have.

http://www.ebay.com/itm/06-09-GMC-Envoy-4-2L-Rear-Axle-39K-Miles-LKQ-OEM-/191464499239?pt=Motors_Car_Truck_Parts_Accessories&hash=item2c942c6827&vxp=mtr
 

Forum Statistics

Threads
23,273
Posts
637,499
Members
18,472
Latest member
MissCrutcher

Members Online