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73-87 Chevy _ GMC Trucks => 4 Wheel Drives => Topic started by: mudnmud on April 27, 2002, 06:37:00 pm

Title: What kind is my rear diff?
Post by: mudnmud on April 27, 2002, 06:37:00 pm

I have a 1975 GMC 1/2 ton 4x4. It has a card in the glove box with all the option codes on it. One of the codes is G80- locking differential. Does anyone know which rear end this is. I am assuming it is a posi-traction rear end. Thanks

Title: Re: What kind is my rear diff?
Post by: 73K20 on April 28, 2002, 10:11:00 pm

Sounds like you have a 12 bolt rear with a Gov-Loc posi traction.  I believe that the Gov-Loc was produced by the Eaton company.  I have never heard a good word about the Gov-Loc other than it DIDNT blow up on the owner.  These posi have a really bad reputation and i have heard many horror stories about them.  Then on the other hand you never hear about he one that work just fine for 30 years with no problems.  Anyhow this is what you have.  The 12 bolt part is the number of bolts that holds the rear cover plate on your differential.

1973 K20 - 350/350/205

Title: Differential
Post by: 79SilveradoK30 on July 24, 2002, 11:07:00 am

Yea, that's the one, the 12-bolt Posi (the option code was identical even for the muscle cars). My truck has that option, but from what I've learned, it doesn't have stock axles. From what I hear it's got a Dana 60 axle in front (independent front suspension), and a Dana 70 in the back.

Title: Re: Differential
Post by: DixieOffroad87 on July 24, 2002, 06:59:00 pm

if u have ifs im sorry cv joints stink! i have gone through 2 on my s10 both on the passenger side

Title: Re: Differential
Post by: 79GMC4x4 on August 07, 2002, 10:52:00 am

A K-30 came stock with a 60 front, but usually the 14 bolt GM axle in the rear.  Ford and Dodge used the 70 rear, with Ford later coming out with a 10.25 inch axle of their own.  Look under your truck, is the axle straight, and using leaf springs?  It cannot be IFS with a 60.  Dana never offered anything like that.  On older Ford 3/4 tons, they did nake IFS 44's and 50's, but not 60's.  And certainly not Chevy's.

'79 GMC shortbed 454 th400 14 bolt FF NP205 Dana 60