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

outlaw · 05-22-2003, 01:34 AM

I was wondering if someone could tell me what my gear ratio is for my 1970 chevy truck with a 307 1/2 ton long wheel base 3 spd on the column, rear coil springs

crazy longhorn · 05-22-2003, 05:36 PM

3.07 & 3.73 were the most common gears in the 1/2 ton trucks(2 wd). most of the stick shift trucks that I have seen were a 3.73 gear. There was a 4.11 ratio offered, but only with 3 spd/OD trans(pretty rare). Im not positive, but think there was a 3.36 ratio in the mix also.....crazyL

dmnall · 05-23-2003, 02:34 AM

From what I have read on the whole gear ration set up, is look at the Glove Box Sticker, if it says something like 4.11 or 3.07's then that is the gear ratio in your truck, Otherwise it is 3.73...

Charlie

outlaw · 05-23-2003, 01:59 PM

Thanks will look when I get home

outlaw · 06-13-2003, 02:06 AM

when I got home I looked in the glove box and it did not say anything about gear ratio's so does that mean that it is a 3.73 or what does that mean,thanks Danny

crazy longhorn · 06-13-2003, 08:22 PM

My bet would be a 3.73 on a stick shift 1/2 ton, the auto trucks generally had a taller rear diff. You can pop the cover & check, or if you are running a tach, figure that 2800-3000 should put you close to 65 mph with a 3.73 gear. crazyL

CJM72CHEVY · 06-18-2003, 06:42 PM

Jack up the rear end, mark the driveshaft and one tire with white marker or something, and see how many drive shaft revolutions it takes to turn the wheel one turn. Or, it might (probably will) be easier to use the tire to turn the driveshaft. Either way, the results will be the same. If it's around 3, you probably have 3.08s. If it takes more than 3.5 but less than 4 full turns, you probably have 3.73s. The other, more time consuming method is to pull the rear cover, count gear teeth, and divide the ring gear count by the pinion gear tooth count. My '72 C-20 doesn't have the gear ratio listed in the glovebox, either. I pulled the cover to change lube, and found it to have 4.58s (32 tooth ring gear and 7 tooth pinion). The 7-32 was also stamped in the end of the pinion gear in plain sight, but that's on an Eaton axle, and you likely have a 12-bolt.

crazy longhorn · 06-18-2003, 11:44 PM

if you opt to pull the cover, the 12 bolt will have the 2 numbers you need stamped on the outer edge of the ring gear. When checking turns of the axle/d shaft, remember that on an open diff, the spider gears will "goof " with your count when figuring ratio. the spiders step up the axle speed when 1 wheel is spinning 2 to 1. thats why a "1 wheel peel" makes so much smoke. crazyL

06-19-2003, 01:21 PM

3.07 was standard at the time, but you had the option to go to a 3.73 if you wanted it. So unless it says on the glovebox door that it was changed out/or someoneless changed it then its a 3.07

05-22-2003, 01:34 AM	#1
outlaw Registered User Join Date: Dec 2002 Location: Leesville, Louisiana Posts: 80	gear ratio? I was wondering if someone could tell me what my gear ratio is for my 1970 chevy truck with a 307 1/2 ton long wheel base 3 spd on the column, rear coil springs

05-22-2003, 05:36 PM	#2
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	3.07 & 3.73 were the most common gears in the 1/2 ton trucks(2 wd). most of the stick shift trucks that I have seen were a 3.73 gear. There was a 4.11 ratio offered, but only with 3 spd/OD trans(pretty rare). Im not positive, but think there was a 3.36 ratio in the mix also.....crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

05-23-2003, 02:34 AM	#3
dmnall Registered User Join Date: Apr 2001 Location: Goleta, CA Posts: 505	From what I have read on the whole gear ration set up, is look at the Glove Box Sticker, if it says something like 4.11 or 3.07's then that is the gear ratio in your truck, Otherwise it is 3.73... Charlie __________________ 1968 C10 Truck LWB Fleetside 1968 C10 Truck SWB Stepside 1994 K2500 Ext Cab Fleetside 2008 Honda Civic Si lease

06-13-2003, 08:22 PM	#6
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	My bet would be a 3.73 on a stick shift 1/2 ton, the auto trucks generally had a taller rear diff. You can pop the cover & check, or if you are running a tach, figure that 2800-3000 should put you close to 65 mph with a 3.73 gear. crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

06-18-2003, 11:44 PM	#8
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	if you opt to pull the cover, the 12 bolt will have the 2 numbers you need stamped on the outer edge of the ring gear. When checking turns of the axle/d shaft, remember that on an open diff, the spider gears will "goof " with your count when figuring ratio. the spiders step up the axle speed when 1 wheel is spinning 2 to 1. thats why a "1 wheel peel" makes so much smoke. crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

05-23-2003, 01:59 PM	#4
outlaw Registered User Join Date: Dec 2002 Location: Leesville, Louisiana Posts: 80	Thanks will look when I get home

06-13-2003, 02:06 AM	#5
outlaw Registered User Join Date: Dec 2002 Location: Leesville, Louisiana Posts: 80	when I got home I looked in the glove box and it did not say anything about gear ratio's so does that mean that it is a 3.73 or what does that mean,thanks Danny

06-18-2003, 06:42 PM	#7
CJM72CHEVY John Deere Tech Join Date: Jun 2003 Location: NEBRASKA Posts: 368	Jack up the rear end, mark the driveshaft and one tire with white marker or something, and see how many drive shaft revolutions it takes to turn the wheel one turn. Or, it might (probably will) be easier to use the tire to turn the driveshaft. Either way, the results will be the same. If it's around 3, you probably have 3.08s. If it takes more than 3.5 but less than 4 full turns, you probably have 3.73s. The other, more time consuming method is to pull the rear cover, count gear teeth, and divide the ring gear count by the pinion gear tooth count. My '72 C-20 doesn't have the gear ratio listed in the glovebox, either. I pulled the cover to change lube, and found it to have 4.58s (32 tooth ring gear and 7 tooth pinion). The 7-32 was also stamped in the end of the pinion gear in plain sight, but that's on an Eaton axle, and you likely have a 12-bolt.

06-19-2003, 01:21 PM	#9
Linus0014 Guest Posts: n/a	3.07 was standard at the time, but you had the option to go to a 3.73 if you wanted it. So unless it says on the glovebox door that it was changed out/or someoneless changed it then its a 3.07



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