Rear end gearing - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Kutzy · 12-18-2011, 03:40 AM

Okay, so I'm trying to figure out what ratio my truck is most likely to have.

It's a 1980 GMC C10 with a SB 350 and an SM465, it has the 12 bolt GM rear-end. What gear ratio was most commonly used in these trucks?

INSIDIOUS '86 · 12-18-2011, 04:02 AM

3.08 or 2.73

silverados are more likely to have the higher ratio but back then gas mileage and highway was the thing so puny gears were used on all but the biggest haulers

Kutzy · 12-18-2011, 04:22 AM

It's a Sierra model so I'm guessing it will have the 2.73 ratio.
Thanks for the heads up.

Keith Seymore · 12-18-2011, 11:03 AM

According to the powertrain chart in the GM Heritage Center archive:

http://www.gmheritagecenter.com/gm-h...olet-Truck.pdf (page 13)

Base is a 2.73. There was a 3.08 available as an option, which would show up on your SPID as RPO HE3. Those were the only two rear axle ratios available with the 350 and the 4 speed manual trans.

Also - if you really want to know for sure you can send them your VIN and $50 and they will pull up the actual invoice for your specific truck, complete with all the RPOs and pricing. It will look something like this:

K

12-18-2011, 03:40 AM	#1
Kutzy Registered User Join Date: Oct 2011 Location: Las Cruces, New Mexico Posts: 29	Rear end gearing Okay, so I'm trying to figure out what ratio my truck is most likely to have. It's a 1980 GMC C10 with a SB 350 and an SM465, it has the 12 bolt GM rear-end. What gear ratio was most commonly used in these trucks? __________________ 1980 GMC C10 Pickup - SBC 350/Muncie SM465 A slow work in progress!

12-18-2011, 04:02 AM	#2
INSIDIOUS '86 Registered User Join Date: Jul 2009 Location: washington Posts: 4,178	Re: Rear end gearing 3.08 or 2.73 silverados are more likely to have the higher ratio but back then gas mileage and highway was the thing so puny gears were used on all but the biggest haulers __________________ 377 sbc thumpr cam autogear m23 muncie 3:73 Detroit trutrac 3''spintech prostreet mufflers xpipe 1 3/4 headers build thread !http://67-72chevytrucks.com/vboard/s...d.php?t=577217 Iroc gauge threadhttp://67-72chevytrucks.com/vboard/s...d.php?t=554511

12-18-2011, 04:22 AM	#3
Kutzy Registered User Join Date: Oct 2011 Location: Las Cruces, New Mexico Posts: 29	Re: Rear end gearing It's a Sierra model so I'm guessing it will have the 2.73 ratio. Thanks for the heads up. __________________ 1980 GMC C10 Pickup - SBC 350/Muncie SM465 A slow work in progress!

12-18-2011, 11:03 AM	#4
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,192	Re: Rear end gearing According to the powertrain chart in the GM Heritage Center archive: http://www.gmheritagecenter.com/gm-h...olet-Truck.pdf (page 13) Base is a 2.73. There was a 3.08 available as an option, which would show up on your SPID as RPO HE3. Those were the only two rear axle ratios available with the 350 and the 4 speed manual trans. Also - if you really want to know for sure you can send them your VIN and $50 and they will pull up the actual invoice for your specific truck, complete with all the RPOs and pricing. It will look something like this: K __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/

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