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Old 02-08-2019, 12:19 AM   #1
racerface
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1981 STD gear ratio

HELP! I am working on a 81 C-10 two wheel drive 10 bolt with some rear end issues. Build tag said that is a GQ1, STD RATIO. Question is what is the standard ratio? I have a 10 bolt GU4, 3:08 gear in it and would like to use it if it's close to the GQ1.
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Old 02-08-2019, 02:37 AM   #2
Big Moose
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Re: 1981 STD gear ratio

Did you look at the plate on the diff itself?
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Old 02-08-2019, 07:50 AM   #3
Dead Parrot
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Re: 1981 STD gear ratio

Unless you know the history of the truck back to first sale, don't trust the build tag. A PO could have changed the gear set.

Simplest is do the spin the tire, count the drive shaft rotations test.

If the rear end is off the truck, just count teeth on the gears.
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Old 02-08-2019, 08:20 PM   #4
racerface
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Re: 1981 STD gear ratio

At the moment axle is still in the truck. The truck has been in family since 1981. Guess I'll do the old rotation trick. Just thought it was odd GM just calls it "The STD Ratio". Thanks for your time Big Moose and Dead Parrot, stay warm!
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Old 02-08-2019, 09:08 PM   #5
Keith Seymore
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Re: 1981 STD gear ratio

Need more detail in terms of engine and trans but the "most base" ratio is 2.73 .

https://www.gmheritagecenter.com/doc...olet-Truck.pdf
(Powertrain charts shown on page 12 - California only - and page 13 - all others - of the pdf)

The reason the base axle is not called out specifically (designated by GQ1) is because it changes numerically based on other powertrain considerations, per the charts.

The optional axles get called out by name because the numerical ratio always stays the same as the RPO code.

Bottom line is, as Dead Parrot said, no telling what's in there after all this time.

K
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Last edited by Keith Seymore; 02-09-2019 at 09:49 AM.
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Old 02-11-2019, 07:25 PM   #6
racerface
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Re: 1981 STD gear ratio

Thanks Keith for the reply. It's a 250 - 6cyl. 350 turbo Hydro farm truck. I'll check out the GM site, thanks again.
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Old 02-11-2019, 09:11 PM   #7
Keith Seymore
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Re: 1981 STD gear ratio

2.73:1 Federal; 3.08 for California emissions.

K
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Old 02-12-2019, 06:21 PM   #8
dagnabbitt
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Re: 1981 STD gear ratio

Mine's an 81 6 cyl (originally) I can confirm that it would be 273
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Old 02-15-2019, 01:09 AM   #9
akart
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Re: 1981 STD gear ratio

So,like rotate your wheel and count how many times the shaft rotates. Done!
There's your ratio.
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Old 02-15-2019, 05:28 AM   #10
mongocanfly
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Re: 1981 STD gear ratio

well ....sorta akart....https://shiftsst.com/articles/how-to...ear-axle-ratio
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Old 02-15-2019, 06:16 PM   #11
akart
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Re: 1981 STD gear ratio

Quote:
Originally Posted by mongocanfly View Post
Thanks for setting that straight. Good answer.
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