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Need help ok n how to identify what rear end is in my 87 caprice 9c1
Do you have the RPO Codes from in the glovebox? Or, how about a picture?
You could also call the parts department at your local Chevy House with your VIN. Of course this only works if the car has never been molested...

Chances are you have a 10 Bolt rear. Either 7.5 or 8.5 ring gear, and you might have to pop the cover to check the carrier for a Posi Unit, and maybe count the teeth to find gear ratio.
 

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Almost certainly an 8.5" 10-bolt.

It will have 10 bolts on the cover. Only possible choices (unless it's been swapped) are the 7.5" and 8.5". Like I said, it's 95% going to be an 8.5", but I have seen some 9C1 and wagon Caprices with 7.5".

This is a 7.5". Notice the "rounded rectangle" cover bolt pattern.
Bumper Motor vehicle Gas Automotive exterior Automotive lighting


This is an 8.5". Notice the very round shape of the cover bolt pattern.

Musical instrument Helmet Gas Auto part Cookware and bakeware
 

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Hates: Liver. Loves: Diesel
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Do you have the RPO Codes from in the glovebox? Or, how about a picture?
You could also call the parts department at your local Chevy House with your VIN. Of course this only works if the car has never been molested...

Chances are you have a 10 Bolt rear. Either 7.5 or 8.5 ring gear, and you might have to pop the cover to check the carrier for a Posi Unit, and maybe count the teeth to find gear ratio.
RPO won't tell you ring gear diameter. The VIN at a dealer will just tell them what the RPO codes are.

No need to pop the cover, you can just do the math by tire diameter and RPM/speed. Posi you can tell by a G80 RPO (if it hasn't been changed) or by lifting the rear tires and seeing if they turn independently. What TYPE of posi is the question. Most likely a cone-style but could be a clutch style.

There is also a stamping on the axle tube that tells you it's original designation. Posi rears came equipped with a tag under one of the cover bolts, but they can break off, get lost, or otherwise lie. If you find the stamping code it will tell you everything.
 
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