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Discussion Starter #1
Does anyone know what spline and what gears come stock with an 85 GMC pickup. Also what kind of posi i would use. Tnx
 

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current hot rod: CTS-V
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Assuming its a regular duty full size truck.

8.5" ten bolt, 30 spline pinion, 28 Spline axles, should be a regular limited slip unit.

Gears varied. Facing forward on the passenger side of the axle housing is a code that if you post it I can tell you what gears you have.
 

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Discussion Starter #4
What kind of gears would you recommend? I have a 350 engine with a turbo 400 trans. Its a 1/2 ton 2 wheel drive.
 

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Even easier than crawling under the truck and having to scrape the axle tube for the code.

Look in the glovebox for the Service Parts Identification decal.
The axle gear ratios all start with the letter G, for example GU6 is the code for 3.42 gears.

There are many sites out there for looking up GM's RPO codes, there are many members here more than willing to help, there is also the possibility of going to the service counter at the local GM dealer and asking them (easy as pulling hen's teeth at times, from my experience).
 
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