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Old 11-06-2002, 05:57 PM
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Post Determining gear ratio on an "OPEN-differential, GM 10-bolt

Just wondering how to quickly determine the ratio of an open diff. GM 10 bolt rear?
The jacking up and turning the wheel or driveshaft seems to produce unuasual results. (like 1.5 : 1)

I have no idea what this rear is out of originally.

Guess I could pull the cover and count teeth!

Thanks,

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Old 11-06-2002, 06:05 PM
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HEY Dude,
The only other way I know how to deal with that is to find out what your rpm is at a certain speed, and crunch the numbers to find out what that would be at the diff. I forget the formula, but you do need to know you trans gears, the diameter of you tires, i'm sure a smart guy like you should be able to figure it out.

Yeah, with open axles, something wierd happens when you try to measure it like that, it only works with positraction rears.

keep on roddin' <img src="graemlins/pimp.gif" border="0" alt="[pimp]" />
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Old 11-06-2002, 06:19 PM
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With an open diff you multiply the reading by two (roughly 2.90-3.08:1 in your case). Through the action of the planetary gears, the wheel spinning (if the other one is still) will spin twice as fast (so you multiply by two). Example: If you power brake the car (with open diff) and the speedo reads 50 MPH, the tire that is spinning is actually spinning 100 MPH. Imagine how fast the planetary gears are spinning!

[ November 06, 2002: Message edited by: BstMech ]

[ November 06, 2002: Message edited by: BstMech ]</p>
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Old 11-06-2002, 06:46 PM
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Thanks,
I'll measure again, this time a little closer. I'll have someone hold the other wheel when doing this.

Tom,
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Old 11-06-2002, 06:52 PM
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Did I say DIVIDE by two?......UH, multiply. <img src="graemlins/drunk.gif" border="0" alt="[drunk]" /> A more accurate way is to let the tire rotate twice while counting the turns of the driveline (holding one wheel).
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Old 11-06-2002, 07:07 PM
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Step UP and do the right thing. Take the 10 bolts out, drain the fluid (you know it needs it) and count the teeth.

Reverse the procedure........
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Old 11-07-2002, 08:25 PM
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I agree, pull the 10 bolts, then look on the ring gear, 2 numbers will be stamped on it, example 12 - 44 Divide them, that will give you your ratio. I`ve seen guys take the cover off and see 41 - 11 stamped on the ring gear and they`ll say "hey,, some 4.11`s!" and i do believe 41 - 11 is 3.73`s
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