What gear ratio do i have?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

84 400 · 12-21-2009, 09:33 AM

I know it has been asked before but i am kinda confused. Looked on the web and still not sure.

For 2 rotations of the tire the pinon turns just over 3 revolutions. The drive shaft is still hooked up and the T case is in N.

This is the stock 10 bolt on a 1977 K10 heavy half with 34 swamper tsl's.

This does not seem right to me i would think the truck would have 3:73 or $:10 but from what i gather this ratio would put my gear set down near 273???

b454rat · 12-21-2009, 09:57 AM

Could be 3.08s, 3.42s. Check on the front diff for a tag held on by a cover bolt, if it's still there it will tell you the ratio.

msgross · 12-21-2009, 10:03 AM

or pull the rear diff cover and check the ring gear for numbers. it will have a ratio like 41:11 = 3.73 etc..

fill it back up with some synthetic oil and never touch it again for the rest of your life... unless you change gears.

84 400 · 12-21-2009, 12:21 PM

yeah i did diff fluid last winter... No tag on the axle. well I do have a diff gau8rd ,ade up that needs install so i guess i will check then. Kinda bummed if its got 308"s

Mike C · 12-22-2009, 10:29 PM

You have one tire on the ground in the back when rotating? That is correct without an LSD. What trans came in the truck? TH350 or TH700? Better gears would have come with the TH700. My dad's '81 Jimmy had 2.56 gears, so it could be worse...

12-21-2009, 09:33 AM	#1
84 400 Sb 400 club Join Date: Nov 2005 Location: NH / MA Posts: 2,746	What gear ratio do i have?? I know it has been asked before but i am kinda confused. Looked on the web and still not sure. For 2 rotations of the tire the pinon turns just over 3 revolutions. The drive shaft is still hooked up and the T case is in N. This is the stock 10 bolt on a 1977 K10 heavy half with 34 swamper tsl's. This does not seem right to me i would think the truck would have 3:73 or $:10 but from what i gather this ratio would put my gear set down near 273??? __________________ 1984 chevy c10, built 400sb,.(SOLD) 77 K10 Project / daily driver "The Grinch" http://67-72chevytrucks.com/vboard/s...d.php?t=318363 1956 Willys Wagon (327 chevy) Project (Now Buick 225) 1980 Corvette L-48 4 speed 1992 Mustang GT built 5.0 5 speed 1985 C10 LWB Sold 1982 K10 SWB plow truck Parted out 1986 D30 M1028 fire brush truck Parted out

12-21-2009, 09:57 AM	#2
b454rat Senior Member Join Date: May 2004 Location: Binghamton, NY Posts: 3,469	Re: What gear ratio do i have?? Could be 3.08s, 3.42s. Check on the front diff for a tag held on by a cover bolt, if it's still there it will tell you the ratio. __________________ 2000 GMC CCSB 454/4L80 6” lift SAS 1999 Chevy CCSB 454/NV4500 4” SAS 1999 GMC Yukon 350/4L60 6" SAS

12-21-2009, 10:03 AM	#3
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: What gear ratio do i have?? or pull the rear diff cover and check the ring gear for numbers. it will have a ratio like 41:11 = 3.73 etc.. fill it back up with some synthetic oil and never touch it again for the rest of your life... unless you change gears. __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer"

12-21-2009, 12:21 PM	#4
84 400 Sb 400 club Join Date: Nov 2005 Location: NH / MA Posts: 2,746	Re: What gear ratio do i have?? yeah i did diff fluid last winter... No tag on the axle. well I do have a diff gau8rd ,ade up that needs install so i guess i will check then. Kinda bummed if its got 308"s __________________ 1984 chevy c10, built 400sb,.(SOLD) 77 K10 Project / daily driver "The Grinch" http://67-72chevytrucks.com/vboard/s...d.php?t=318363 1956 Willys Wagon (327 chevy) Project (Now Buick 225) 1980 Corvette L-48 4 speed 1992 Mustang GT built 5.0 5 speed 1985 C10 LWB Sold 1982 K10 SWB plow truck Parted out 1986 D30 M1028 fire brush truck Parted out

12-22-2009, 10:29 PM	#5
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,728	Re: What gear ratio do i have?? You have one tire on the ground in the back when rotating? That is correct without an LSD. What trans came in the truck? TH350 or TH700? Better gears would have come with the TH700. My dad's '81 Jimmy had 2.56 gears, so it could be worse... __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax



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