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post #1 of (permalink) Old 08-06-2001, 02:08 PM Thread Starter
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79 12 bolt question (gear ratio)

got some axles off a 79 blazer. my friend and i tried to figure out what the gear ratio was last night by turning the axle and counting the number of times the yoke rotated - 1.5 times... this doesn't sound right - the truck had a 350/350/203. both the front and rear were 1.5... anyone care to enlighten me on this... i did it on my 89 s-10 and it was a 3.73... we tried to figure out if the 203 had a reduction in it, but it doesn't... thanks all


'89 S-10 P/U 4.3L 31" Yoko M/Ts
'99 S-10 2.2L 2WD 5 Speed Stepside Totally Stock [img]/wwwthreads_images/icons/frown.gif[/img]
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post #2 of (permalink) Old 08-06-2001, 02:20 PM
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Re: 79 12 bolt question (gear ratio)

If you have one wheel in the air, and one on the ground, you have to turn the tire two revolutions to read the gear ratio directly from the driveshaft. I would guess that you have 3.07 gears (1.5 X 2). That was pretty much the standard ratio for trucks with a 350 in the '70s.

'70 CST Blazer, 350, SM465, NP205.
'87 Suburban 4X4, 350, 700R4
'01 GMC 2500HD, Duramax/Allison
post #3 of (permalink) Old 08-26-2001, 03:43 PM
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Re: 79 12 bolt question (gear ratio)

3.08 is most likely what it has. My 79 had the same drivline set up and that is what it had stock. The most accurate way of checking is to locate the stamp in the axle tube. Write down the letter/number combo and call you local chev dealer. They will be able to look it up and let you know what the ratio in that axle was.

79 Blazer,4x4, modified 350cid, 33", 4.10 gears
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post #4 of (permalink) Old 08-26-2001, 09:27 PM
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Re: 79 12 bolt question (gear ratio)

the most postive way to tell what ratios you have is to pull the covers off and see what is stamped on the ring gear it will have numbers on it like 11 and 41 divide it this is a 3.73 or so on it will also have a date on them also while you have the cover off look for damage and put new gear oil back in

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