So I'm planning on doing a well-needed diff fluid change with a new cover in my 2003 GMC Yukon Denali and I wanted to know what specific rear differential do I have. I know its a 10 bolt but I've seen different variations of 10 bolts from older to newer cars regarding the size of something in inches (Diff itself or axle I'm not sure). I may be wrong but if parts like ARP diff cover bolts say they fit "select 10 bolt GM differentials" would it be safe to assume it would fit my truck?
What Rear Diff Do I Have?
- Thread starter Bxcliff
- Start date
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wjburken
Supporting Member
Post a picture of the RPO sticker that is inside your glove box. It looks like this.
If you can get a picture of the rear cover of the differential, that would help as well.
swathdiver
Full Access Member
It's an AAM 8.6" 10-Bolt. Same cover used on old Buick GNs with their 8.5" ring gear and many other since the 1980s.
S33k3r
Full Access Member
This is what Google returned:
GT4 : AXLE REAR, 3.73 RATIO (DUP WITH 5 X 1)
I know GT4 is 3.73 gearing, but don't know what "DUP WITH 5 x 1" means.
You can try this site to decode more if you are interested:
https://www.carinspector.us/blog/15-ask-an-expert/171-gm-rpo-decoder
GT4 : AXLE REAR, 3.73 RATIO (DUP WITH 5 X 1)
I know GT4 is 3.73 gearing, but don't know what "DUP WITH 5 x 1" means.
You can try this site to decode more if you are interested:
https://www.carinspector.us/blog/15-ask-an-expert/171-gm-rpo-decoder
wjburken
Supporting Member
5X1 is an RPO code that means the same thing as GT4.
Yes, GT4 is 3.73 and I have the same and love that gear but what is the code for limited slip so he can get the right fluid?
Never mind, G80 is the limited slip and he does not show that. It's an open differential.
Never mind, G80 is the limited slip and he does not show that. It's an open differential.
S33k3r
Full Access Member
Actually, G80 is a locking differential. There is a threshold that has to be reached, but once it is reached, it is locked. G86 is the limited slip differential. How am I so sure? My '05 Suburban and my '04 Silverado both have the G86; the '03 Sierra I have used to have a G80 (rear) AND a G86 (front). But i replaced the front differential and did not catch that it also had a G86 in it.
Thanks for your help guys, I never knew about the RPO codes until now. I was looking at the list of all the codes on that website and it's pretty cool. It now makes sense to me why the 6.0 in my truck is called LQ4 
So if anyone were to ask me what differential/rear-end I have, it would be RPO code: GT4 (3.73 gearing), and its also a GM 10 bolt 8.5'' diff.
So if anyone were to ask me what differential/rear-end I have, it would be RPO code: GT4 (3.73 gearing), and its also a GM 10 bolt 8.5'' diff.
HiHoeSilver
Away!
Thanks for your help guys, I never knew about the RPO codes until now. I was looking at the list of all the codes on that website and it's pretty cool. It now makes sense to me why the 6.0 in my truck is called LQ4
So if anyone were to ask me what differential/rear-end I have, it would be RPO code: GT4 (3.73 gearing), and its also a GM 10 bolt 8.5'' diff.
Technically, its 8.6, but you will see the cover listed as "GM corporate 10 bolt, 8.5-6"
Also, can't recommend the Lubelocker gasket highly enough.
Edit: part # LLR-G850
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