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08-25-2024, 12:28 PM
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#1 |
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Registered User
Join Date: Jun 2009
Location: COOKEVILLE,TN
Posts: 147
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'67 12 bolt gear ratio
I have a '67 Chevy SWB frame with a 12 bolt....trying to figure the ratio, best I can tell it comes out to be a 340. I don't know if it's really a 336,342 or 355. Guess I'll have to pull the cover off. I think it was an I6.
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08-25-2024, 01:23 PM
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#2 |
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State of Confusion!
  
Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 47,082
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Re: '67 12 bolt gear ratio
If your count is correct it is probably a 3.42. I have not heard of a 3.55 or 3.36 used on GM trucks.
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Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! |
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08-25-2024, 02:36 PM
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#3 | |
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Senior Member
Join Date: Feb 2002
Location: Tucson, AZ USA
Posts: 7,424
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Re: '67 12 bolt gear ratio
Quote:
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
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08-25-2024, 07:13 PM
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#4 | |
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Registered User
Join Date: Jun 2009
Location: COOKEVILLE,TN
Posts: 147
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Re: '67 12 bolt gear ratio
Quote:
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08-25-2024, 08:36 PM
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#5 |
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Registered User
Join Date: Feb 2024
Location: Pleasanton CA
Posts: 232
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Re: '67 12 bolt gear ratio
Factory i6, should be 3.73 which is an awesome ratio
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1969 C10 Shortbed |
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08-26-2024, 08:44 PM
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#6 |
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Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,723
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Re: '67 12 bolt gear ratio
3.40 was a factory gear set in the mid 70’s for a couple of years. They are not super common, but you come across them. 34 teeth on the ring gear and 10 on the pinion. Not 3.42 ratio like you would find in a 10 bolt. As mentioned above, 3.73 would have been the standard gear in your truck. Any option would be listed on the SPID.
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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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08-27-2024, 07:14 AM
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#7 |
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Senior Member
Join Date: Aug 2003
Location: Conyers,Ga.
Posts: 7,288
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Re: '67 12 bolt gear ratio
I know in 50 plus yrs It could’ve been changed, but you could always check the code on the axle tube. Should be on the passenger side between the trailing arm mount and carrier housing. It usually anywhere from 12 to 3 o’clock on the tube.
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08-28-2024, 12:00 AM
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#8 |
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The Older Generation
 
Join Date: Aug 2006
Location: Montezuma, Iowa
Posts: 25,637
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Re: '67 12 bolt gear ratio
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If you find the code on the axle tube or housing here are the conversion charts I posted a few years ago. http://67-72chevytrucks.com/vboard/s...d.php?t=578793 Check posts #8 & #19 for a couple of the code stamp locations.. .
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Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - |
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08-28-2024, 04:04 PM
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#9 |
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Senior Member
Join Date: Jan 2016
Location: Sugar Hill GA
Posts: 369
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Re: '67 12 bolt gear ratio
If you don't want to pull the diff cover you can use these two calculators.
Get you tire size https://tiresize.com/calculator/ To find you gear ratio take the truck out and use your GPS to get an accurate MPH and a tach to get your RPM in top gear at like 70mph. Then put all that info onto https://www.summitracing.com/popup/c...iAAEgIFzvD_BwE
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1967 C10 Step side 1970 AMX 390 1977 Datsun 280Z highly modified with '95 LT1 power |
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