I know that this isnt for a third gen, but I need to find out how you tel the difference between these 2 is it rear end cover or nust numbers on the axel tube? anyone help please!
thanks

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'87 Monte Carlo SS,with '89 IROC 350,700 trans, blew up 3.73 posi stuck with crappy 2.73's neeed gears! hooker headers, flow's 2 1/2" exhaust true dualls

 

You can tell them apart by the diff cover. It is hard to explain, and I wish I had a picture to show you the difference. The 7.5" has an overall shape of a square with round corners, whereas the 8.5", the raised section almost resembles a football. You probably won't understand all if this unless you see them side by side. If I can find a picture tomarrow, I will post so you can see the difference.

P.S. they are both a 10-bolt.

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"I used to have a handle on life, but then I used it as a plunger and broke it" -The Wave

ASE Master Tech + L1
Savannah, GA
'87 Trans Am-K&N,Cold air induction, SSM SFC, Flowmaster, 16" GTA rims.
'97 Bonneville SSE
About Me

 

Hey monte-ss, one really good way of telling the G-BODY 8.5" over the 7.5" is to look right below the pan of your 7.5" rear and you will see some extensions that look like nipples. The 8.5" rear has larger extensions that are 90 angled verses nipples. I've had my 87 442 3.73:1 G-80 8.5" rear in my SS for 6-years now and it is great. Just look at any 1500 chevy pickup rearend and you will see specifically what the extensions on the 8.5" rearend look like. The 8.5" come in the 84-87 GN and T/R with a 3.42 gear, NOT all GN/TR come with G-80, some are open rears. The 83-84 HURST OLDS and the 85-87 OLDS 442 come with a 3.73:1 gear, mine just happen to be a G-80. The 8.5" rears in the G-body are a 28-spline axle EATON unit and are very strong, if you want to upgrade, you can get an 8.5" EATON out of an 89-up 1500 CHEVY or GMC truck with the 30-spline and get some MOSER 30-spline G-body axles. The EATON units are good units and don't waste money buying an AUBURN piece, you can easily rebuild the EATON unit for LESS THAN HALF what it cost for a new AUBURN. HTH's email me if you have any questions. SS-ya.

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88 Monte SS 355 TPI/LT-4 HOT CAM/AFR Hydra-rev/ T-56 6-Speed

 

thanks guys I think I understand, 6SPD , gbody88 has a 8.5 as well and was telling me a little about it I just couldnt figure out the difference. If I have any more Q's Ill email ya
thanks again
Monte-ss