2WD standard axles - The 1947 - Present Chevrolet & GMC Truck Message Board Network

C15_Sierra · 04-19-2011, 09:54 AM

The truck is a 1980 GMC LWB, originally with a 250/3spd manual. As far as I know the rear axle is original, and according to the service tag it has the "standard" rear axle - no gearing information.

I'm looking to convert to posi, what spline axle would I have in the rear? And just out of curiousity, what was considered the "standard gearing?" Truck is a base model that used to be I6, from what I've read its either 3.42 or 3.73

Thanks!

lilpoindexter · 04-19-2011, 10:59 AM

My 78 straight six, 3 speed manual truck, came with a 3.73 12 bolt

**N2TRUX** · 04-19-2011, 11:33 AM

We can guess, but your going to need to know for sure. You need to verify if its a 10 bolt or 12 bolt to start with. From there you will need to determine what carrier it currently has if you plan to change gears along with the posi. If it has a 3 series carrier, you can go as low as 3.56. If it has a 4 series carrier it will go 3.73 and below.

C15_Sierra · 04-19-2011, 03:13 PM

I think its a 12-bolt but I can check after work today. How can I tell between the a 3-series and 4-series carrier?

C15_Sierra · 04-19-2011, 10:15 PM

It is indeed a 12-bolt...what's the difference between a 3- and 4-series carrier?

Thanks!

04-19-2011, 09:54 AM	#1
C15_Sierra Registered User Join Date: Apr 2011 Location: Hartford CT Posts: 223	2WD standard axles The truck is a 1980 GMC LWB, originally with a 250/3spd manual. As far as I know the rear axle is original, and according to the service tag it has the "standard" rear axle - no gearing information. I'm looking to convert to posi, what spline axle would I have in the rear? And just out of curiousity, what was considered the "standard gearing?" Truck is a base model that used to be I6, from what I've read its either 3.42 or 3.73 Thanks! __________________ -Steve 1980 GMC C15 Sierra LWB Dark Carmine Red/Carmine Int Was: 250/3spd (1980-88), then a 305/TH350 (1988-2011) Now: 5.3/4L60E, 2.73 12-bolt open rear

04-19-2011, 10:59 AM	#2
lilpoindexter Registered User Join Date: Sep 2010 Location: los angeles Posts: 1,134	Re: 2WD standard axles My 78 straight six, 3 speed manual truck, came with a 3.73 12 bolt

04-19-2011, 11:33 AM	#3
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,021	Re: 2WD standard axles We can guess, but your going to need to know for sure. You need to verify if its a 10 bolt or 12 bolt to start with. From there you will need to determine what carrier it currently has if you plan to change gears along with the posi. If it has a 3 series carrier, you can go as low as 3.56. If it has a 4 series carrier it will go 3.73 and below. __________________ Follow me on Facebook and Instagram @N2trux.com Articles- "Jake" the 84 to 74 crewcab "Elwood" the77_Remix 85 GMC Sierra "Scarlett" "Refining Sierra"

04-19-2011, 03:13 PM	#4
C15_Sierra Registered User Join Date: Apr 2011 Location: Hartford CT Posts: 223	Re: 2WD standard axles I think its a 12-bolt but I can check after work today. How can I tell between the a 3-series and 4-series carrier? __________________ -Steve 1980 GMC C15 Sierra LWB Dark Carmine Red/Carmine Int Was: 250/3spd (1980-88), then a 305/TH350 (1988-2011) Now: 5.3/4L60E, 2.73 12-bolt open rear

04-19-2011, 10:15 PM	#5
C15_Sierra Registered User Join Date: Apr 2011 Location: Hartford CT Posts: 223	Re: 2WD standard axles It is indeed a 12-bolt...what's the difference between a 3- and 4-series carrier? Thanks! __________________ -Steve 1980 GMC C15 Sierra LWB Dark Carmine Red/Carmine Int Was: 250/3spd (1980-88), then a 305/TH350 (1988-2011) Now: 5.3/4L60E, 2.73 12-bolt open rear



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