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Old 10-14-2018, 05:02 PM   #1
Warrens69GMC
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Axle ratio?

Whats the 12 bolt axle ratio?

12:32, 12:42?

1979 Suburban, 454, TH400, 12 bolt and 7000gvw
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Old 10-14-2018, 05:35 PM   #2
geezer#99
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Re: Axle ratio?

Clean it off and have a better look.
Usually the ratio is stamped with the ring gear number first and the pinion gear second.
That might be a part number you’re looking at.
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Old 10-14-2018, 09:23 PM   #3
mongocanfly
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Re: Axle ratio?

im with geezer....but if 12:42 is correct (even backwards) that works out to 3.50:1....since you've got the cover off itll be real easy to do the ol spin and count rotations
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Old 10-15-2018, 01:41 PM   #4
Keith Seymore
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Re: Axle ratio?

Your choices are 2.76 (base), 3.07, 3.40 or 3.73 (optional).

Teeth are:

2.76 = 17/47
3.07 = 14/43
3.40 = 10/34
3.73 = 11/41

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Old 10-15-2018, 01:55 PM   #5
Keith Seymore
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Re: Axle ratio?

I show a 8&1/2" ring gear 3.42 that's 12 and 41, but since that is not one of the choices above that would imply it's not the original axle.

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Old 10-15-2018, 02:54 PM   #6
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Re: Axle ratio?

Warren, is it a C10 or C20? Keith posted 7k gvw options in C10 based on your post..

is it possibly 4.XX ratio 3/4t axle? I recall Keith posting recently about gvw groupings, maybe a factor here?

simplest thing to do at this point, is clean off a spot on the ring gear, mark a tooth with junk yard pen, and count..

if you can, do the same on the pinion.. maybe a mirror and light will make it possible..

compare your numbers to the factory options Keith posted and see if you're close..

if you're unsure due to access to the pinion teeth, count revs to see what neighborhood you're in..

good luck!
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Old 10-15-2018, 04:21 PM   #7
Warrens69GMC
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Re: Axle ratio?

Its a 5 lug 12 bolt. I will get under there again with some rags and brake cleaner to see if I can find more numbers.
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Old 10-15-2018, 09:33 PM   #8
Warrens69GMC
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Re: Axle ratio?

Getting back under found 11:41 = 3.73

Thank guys!!
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Old 10-16-2018, 12:08 AM   #9
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Re: Axle ratio?

Are you planning on changing gears or just looking for info purposes? Is it me or do a couple of those ring teeth look a bit rough? Maybe its nothing.
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Old 10-16-2018, 12:13 AM   #10
Warrens69GMC
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Re: Axle ratio?

I was more curious than anything, this Suburban has set for a while, so it needs new fluids anyway. The SPID is long gone, so that was not an option.
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