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06-02-2004, 02:49 PM
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#1 |
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Registered User
Join Date: Jun 2004
Location: Central Texas
Posts: 4
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Gmc gear ratio
I have a 1976 GMC Sierra Classic 1/2 ton pickup. It orginally came with a 350 sbc and a 4bbl carb. This truck also has the heavy duty chasis with the 350 trans. I would like to know what gear ratio my 12 bolt orginally came equipped with. Thanks for any help.
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06-02-2004, 02:55 PM
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#2 |
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Registered User
Join Date: Oct 2002
Location: Phoenix, Arizona
Posts: 4,703
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Welcome to the forum..... best on the net.
Lots of great guys and gals with tons of info! I believe they came in many different ratios. Only way to know for sure what gears you have is to take the cover off and count the teeth. Probably time to change the fluid anyways. I think some rear ends had tags on them and some have numbers on the tube which can help identify the ratio if nobody changed it. You can do the tire and driveshaft thing but I dont know how accurate that is. Others will have more info on identifing them without taking off the cover and counting the teeth.
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06-03-2004, 09:53 AM
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#3 |
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Registered User
Join Date: Jul 2001
Location: Atlanta GA
Posts: 1,704
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On one of the axle tubes is some numbers. I think there is a way to figure out the ratio from those numbers.
In your glove box should be a sticker that has the RPO codes. If an option gear was installed it will be on one of those codes. No code it's the default gear and that is usualy 3.08 in the mid 70's on V8 trucks with Auto.
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Grim-Reaper 70 Pontiac LeMans Sport Convertible, worlds longest resto in progress Looking for 71-72 2wd Blazer or Jimmy Project |
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06-03-2004, 02:14 PM
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#4 |
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Registered User
Join Date: May 2004
Location: Llano,TX
Posts: 113
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My dad has almost the identical truck, but it's a '75. It's got 3.08's for sure. They are easy to check doing the jack a tire up and turn it 2 rotations. The driveshaft should rotate a hair over 3 times for 3.08's.
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‘66 Chevy C-10, long bed fleetside, 350, 3 on the tree, 4-7 drop. '77 chevy C-10 Custom Deluxe, 350, SM465 4 speed, flatbed. '80 jeep CJ-5. ‘14 Chevy 1500 Z71… |
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06-03-2004, 03:00 PM
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#5 |
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Oh,you can't buy that new
 
Join Date: Apr 2000
Location: Pennsville,N.J. 08070, USA
Posts: 2,039
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most 76's were stamdard with 3.40 ratio. there are numbers stamped into the right(passenger side) axle tube near the top. I clean them off with a file. It will be like KAS or RTB or something like that. I have most of the codes,but there are thousands over the 73-87 years . If it still has the option sheet in the glove box and nothing is listed it is prolly the standard 3.40 ratio for that year. These trucks have all had SOMETHING changed by now. Welcome to the forums. DAVE
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"been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone  73 Pinto, stock, w/CragarSS's-eww  LOTS of Cummins trucks. |
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