What rear diff is in my truck?

[BILTIT]

But they are a different ring gear size.

Housings changed, I was unclear what else, if anything changed, but apparently just the housing and the ring/pinion. Not surprising its the same as the 7.5/7.625.

Are you referring to the 8.6 vs 8.5? The 8.6 uses a 8.5 ring gear or so i have read. I have never had one in my hands to measure.

http://www.ringpinion.com/DiffDetai...ff&TypeID=5&Type=GM&DiffID=46&DiffName=GM+8.6

 

[dyeager535]

I see 8.625" everywhere, no reason it would be anything other than the ring gear size, no other GM axle measurement in inches I'm aware of is anything other than the ring gear diameter.

Can't find anything in GM's specs, but I don't have a new service manual.

Probably not really an issue if the 8.5" stuff swaps in, aftermarket probably sees no point in making two ring gear sets that close in size.

 

[BILTIT]

I see 8.625" everywhere, no reason it would be anything other than the ring gear size, no other GM axle measurement in inches I'm aware of is anything other than the ring gear diameter.

Can't find anything in GM's specs, but I don't have a new service manual.

Probably not really an issue if the 8.5" stuff swaps in, aftermarket probably sees no point in making two ring gear sets that close in size.

They both use 8.5'' parts, check this parts list.

http://www.differentials.com/pdfs/28.pdf

The only difference i see is at the very bottom. Looks like they changed (probably beefier) the carrier.

 

[dyeager535]

I can't answer definitively for 8.5/8.625, but the 7.5 and 7.625 diff's also use *interchangeable* parts, but that doesn't mean they were the same originally, and they weren't.

Why make two different parts if the smaller/cheaper one is interchangeable?

The bearings might also be different, since the installation kits are year specific.