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

BowTieMan · 10-24-2005, 09:59 PM

Are there any number stamped on my axle in my 70 half ton 12 bolt that can tell me my gear ratio?

Longhorn Man · 10-24-2005, 10:18 PM

why not drain the 10+ year old oil (if not 35 year old) and count the teeth while you are in there?

BowTieMan · 10-24-2005, 10:33 PM

I am going to be doing that soon. But I wasn't sure if there was a simpler way that I could see now. I am going to do the oil this weekend.

al's71gmc · 10-24-2005, 10:40 PM

The ratio numbers will be stamped on the ring gear. 4 digit #. divide the little # into the big #. You can also jack up the rear of the truck, spin the wheel and count the revs of the driveline. that will get you close, without pulling the cover.
Edit-If it has an optional set of gears in it, it will tell you on the glove box sticker.

**special-K** · 10-24-2005, 11:15 PM

No tab on a cover bolt?I always do the spin and count.The ratios are around 1/3 of a turn apart,it`s obvious what you have.A little more than 3=3.08,about 3 1/2=3.40,a little less than 4=3.73,a little more than 4=4.10,etc.

Longhorn Man · 10-25-2005, 12:07 AM

what engine/tranny combo did it come with...and was there a gear option listed?

BowTieMan · 10-25-2005, 01:09 AM

350 engine and th350 trans, and no I didn't see any option other then a limited slip.

I know on my uncles f-250 it is stamped on the housing. Wasn't sure if chevy did that too back then.

I'll just pull the cover and see this weekend. How much is the new gasket and the fluid?

Blazer1970 · 10-25-2005, 06:57 AM

If it came with a 350, it has 3.07 gears unless an optional ratio is listed on the sticker.

72str8flush · 10-25-2005, 01:10 PM

As an alternative, here is how I figured my gear ratio, which is only good if you have a Tach.

http://www.chevelles.com/shop/ratios.html

patrolman808 · 10-25-2005, 02:24 PM

What would a truck with the 250/3spd possibly have in it? Never pulled my cover to count the teeth. But it was really low geared with the 350/350 I put in it about 10 yrs ago.

Longhorn Man · 10-25-2005, 07:45 PM

the 3.07 gear came with small block and automatic...either manual tranny would net you a 3.73.
The inline with 3 speed...also a 3.73.

10-24-2005, 09:59 PM	#1
BowTieMan Registered User Join Date: Dec 2003 Location: Glendale Arizona Posts: 747	Gear Ratio Are there any number stamped on my axle in my 70 half ton 12 bolt that can tell me my gear ratio? __________________ "A true hotrodder wouldn't be content untill he had created a car so violent, so hairy, so totally sick that the very act of dropping the hammer would result in instant death. Anything less results in the need to go faster." - Tony DeFeo Last edited by BowTieMan; 10-24-2005 at 09:59 PM.

10-24-2005, 10:18 PM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Gear Ratio why not drain the 10+ year old oil (if not 35 year old) and count the teeth while you are in there?

10-24-2005, 10:33 PM	#3
BowTieMan Registered User Join Date: Dec 2003 Location: Glendale Arizona Posts: 747	Re: Gear Ratio I am going to be doing that soon. But I wasn't sure if there was a simpler way that I could see now. I am going to do the oil this weekend. __________________ "A true hotrodder wouldn't be content untill he had created a car so violent, so hairy, so totally sick that the very act of dropping the hammer would result in instant death. Anything less results in the need to go faster." - Tony DeFeo

10-24-2005, 10:40 PM	#4
al's71gmc 4 eyed fever Join Date: Jul 2005 Location: Eureka, Nevada Posts: 500	Re: Gear Ratio The ratio numbers will be stamped on the ring gear. 4 digit #. divide the little # into the big #. You can also jack up the rear of the truck, spin the wheel and count the revs of the driveline. that will get you close, without pulling the cover. Edit-If it has an optional set of gears in it, it will tell you on the glove box sticker. __________________ 1971 GMC 2500 4x4 1972 GMC Sierra Grande 1/2 t 4x4-#1 son's truck. Recently completed resto. 4 YO daughter," Daddy, I like your truck better than Mom's." (2000 F350-ranch truck) Smart kid!! Last edited by al's71gmc; 10-24-2005 at 10:41 PM.

10-24-2005, 11:15 PM	#5
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	Re: Gear Ratio No tab on a cover bolt?I always do the spin and count.The ratios are around 1/3 of a turn apart,it`s obvious what you have.A little more than 3=3.08,about 3 1/2=3.40,a little less than 4=3.73,a little more than 4=4.10,etc. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

10-25-2005, 12:07 AM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Gear Ratio what engine/tranny combo did it come with...and was there a gear option listed?

10-25-2005, 01:09 AM	#7
BowTieMan Registered User Join Date: Dec 2003 Location: Glendale Arizona Posts: 747	Re: Gear Ratio 350 engine and th350 trans, and no I didn't see any option other then a limited slip. I know on my uncles f-250 it is stamped on the housing. Wasn't sure if chevy did that too back then. I'll just pull the cover and see this weekend. How much is the new gasket and the fluid? __________________ "A true hotrodder wouldn't be content untill he had created a car so violent, so hairy, so totally sick that the very act of dropping the hammer would result in instant death. Anything less results in the need to go faster." - Tony DeFeo

10-25-2005, 06:57 AM	#8
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,510	Re: Gear Ratio If it came with a 350, it has 3.07 gears unless an optional ratio is listed on the sticker. __________________ Tim

10-25-2005, 01:10 PM	#9
72str8flush Registered User Join Date: Aug 2005 Location: Tennyson, Indiana 47637 Posts: 137	Re: Gear Ratio As an alternative, here is how I figured my gear ratio, which is only good if you have a Tach. http://www.chevelles.com/shop/ratios.html __________________ 72 Chevy Short Bed Fleet: 350/TH350 - Sold - Now trying to sell the parts that I have left over. _______________________ 2006 VW GTI

10-25-2005, 02:24 PM	#10
patrolman808 Registered User Join Date: Oct 2005 Location: Northeast Texas Posts: 18	Re: Gear Ratio What would a truck with the 250/3spd possibly have in it? Never pulled my cover to count the teeth. But it was really low geared with the 350/350 I put in it about 10 yrs ago. __________________ 70 C10 Stepside, '68 Front clip. No motor/tranny. 69 Firebird LS1/6spd project(sold) 01 Trans Am WS6,red/black,A4, 17x9.5 L.G. Motorsports G2 wheels 275s/315s, DirectFlow lid,QTP cutout.

10-25-2005, 07:45 PM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Gear Ratio the 3.07 gear came with small block and automatic...either manual tranny would net you a 3.73. The inline with 3 speed...also a 3.73.



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