Gear ratio??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

slick78 · 11-21-2011, 01:44 AM

Can anybody please tell me what gear ratio i have in my 78 c10?. It has a straight six 250ci,it came with a 3 speed on the colom but i changed it to automatic turbo 350 tranny. Thanx!
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shawno72 · 11-21-2011, 01:54 AM

My 68 292 has 3.73 gears with a 4 on the floor
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slick78 · 11-21-2011, 02:54 AM

I think thats what i got 3.73's, but iam not too sure.
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Keith Seymore · 11-21-2011, 07:18 AM

Per the Powertrain Chart in the archives at the GM Heritage Center, base axle ratio is a 3.07:1.

http://www.gmheritagecenter.com/gm-h...olet-Truck.pdf (page 5)

Optional ratios are usually shown on the SPID label. Do you still have the SPID label on it? Does it show a ratio on the label, like "GU6" (3.42) or "GT4" (3.73)?

At any rate, all this assumes it's never been changed. The only way to know for sure is to pull the cover and count teeth. Change the fluid while you are in there -

K

Keith Seymore · 11-21-2011, 08:27 AM

Quote:

Originally Posted by Keith Seymore

Per the Powertrain Chart in the archives at the GM Heritage Center, base axle ratio is a 3.07:1.

http://www.gmheritagecenter.com/gm-h...olet-Truck.pdf (page 5)

Shown on page 15 as well - 3.07:1 standard.

K

Keith Seymore · 11-21-2011, 07:20 AM

As an aside, if you have the ability to travel a measured distance in a certain amount of time, then we can calculate the rear axle ratio using the "N/V" ratio formula.

Let me know if you want more detail on that.

K

D13 · 11-21-2011, 08:04 AM

My 84 250/TH350C has 3.08's
My 81 3/4 ton 250/3OTT has 3.43's
My 77 250/3OTT has 2.7? 's

slick78 · 11-21-2011, 12:26 PM

I just changed the fluid,but i forgot to check. Iam guna open up the cover again anyway because i got a little leak. Its more likely my gasket. Then this time ill count.
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slick78 · 11-21-2011, 12:35 PM

Gmheritagecenter helps alot. Thanx!
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11-21-2011, 01:44 AM	#1
slick78 Registered User Join Date: May 2008 Location: salinas,california Posts: 144	Gear ratio??? Can anybody please tell me what gear ratio i have in my 78 c10?. It has a straight six 250ci,it came with a 3 speed on the colom but i changed it to automatic turbo 350 tranny. Thanx! Posted via Mobile Device

11-21-2011, 01:54 AM	#2
shawno72 C/10 junkie Join Date: Nov 2010 Location: Stockton Ca Posts: 9,094	Re: Gear ratio??? My 68 292 has 3.73 gears with a 4 on the floor Posted via Mobile Device __________________ Shawn 70 LWB C10 current driver/project http://67-72chevytrucks.com/vboard/s...d.php?t=663051 68 SWB C10 Work in progress.....SOLD http://67-72chevytrucks.com/vboard/s...d.php?t=559520 72 LWB C10 Sold 71 LWB C10 Sold 68 LWB C10 CST Sold http://youtu.be/kbB0QrBIs9k My mom always had the best advice. It was just a tad late. After a fall that involved blood, she'd say....."Careful!"

11-21-2011, 02:54 AM	#3
slick78 Registered User Join Date: May 2008 Location: salinas,california Posts: 144	Re: Gear ratio??? I think thats what i got 3.73's, but iam not too sure. Posted via Mobile Device

11-21-2011, 07:18 AM	#4
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,237	Re: Gear ratio??? Per the Powertrain Chart in the archives at the GM Heritage Center, base axle ratio is a 3.07:1. http://www.gmheritagecenter.com/gm-h...olet-Truck.pdf (page 5) Optional ratios are usually shown on the SPID label. Do you still have the SPID label on it? Does it show a ratio on the label, like "GU6" (3.42) or "GT4" (3.73)? At any rate, all this assumes it's never been changed. The only way to know for sure is to pull the cover and count teeth. Change the fluid while you are in there - 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/

11-21-2011, 07:20 AM	#6
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,237	Re: Gear ratio??? As an aside, if you have the ability to travel a measured distance in a certain amount of time, then we can calculate the rear axle ratio using the "N/V" ratio formula. Let me know if you want more detail on that. 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/

11-21-2011, 08:04 AM	#7
D13 Registered User Join Date: Feb 2007 Location: Memphis MI Posts: 1,851	Re: Gear ratio??? My 84 250/TH350C has 3.08's My 81 3/4 ton 250/3OTT has 3.43's My 77 250/3OTT has 2.7? 's __________________ 1987 2 ton 1982 250/TH350 beater in progress Dad's 1981 3/4 L6 3 on tree posi and no options, awaiting restoration or scrapping Plus a mess o' tractors

11-21-2011, 12:26 PM	#8
slick78 Registered User Join Date: May 2008 Location: salinas,california Posts: 144	Re: Gear ratio??? I just changed the fluid,but i forgot to check. Iam guna open up the cover again anyway because i got a little leak. Its more likely my gasket. Then this time ill count. Posted via Mobile Device

11-21-2011, 12:35 PM	#9
slick78 Registered User Join Date: May 2008 Location: salinas,california Posts: 144	Re: Gear ratio??? Gmheritagecenter helps alot. Thanx! Posted via Mobile Device



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