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Old 12-10-2008, 09:04 PM   #1
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How to check gear ratio without removing diff cover?

Can anyone tell me the way to check this?
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Old 12-10-2008, 09:16 PM   #2
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Re: How to check gear ratio without removing diff cover?

#driveshaft rotations:#axle rotations
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Old 12-10-2008, 09:18 PM   #3
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Re: How to check gear ratio without removing diff cover?

Block the front tires good.....Jack the rear tires off the ground.....Put the car in Neutral..Crawl under & rotate a rear wheel 1 full revolution.....Count the # of times it takes the driveshaft/pintion yoke to rotate 1 full revolution.

You'll end up close to 2 3/4 turns for something like 2.73s....3 full turns for a 3.08....3 1/4 turns for 3.23....So on & so on.

Now, it also depends on if you have a 9-bolt or 10 bolt. Like the 9-bolts got 3.27 & 10 bolts got 3.23s, for the "equal" gear ratio.

This needs to be made into a sticky..I feel like I answer this every 2 or 3 weeks!

Last edited by Stephen; 12-10-2008 at 09:30 PM. Reason: typo
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Old 12-10-2008, 10:33 PM   #4
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Re: How to check gear ratio without removing diff cover?

You should be rotating both wheels to get an accurate calculation. Rotating one wheel will have the spider gears turning also and won't be turning the ring gear at the proper speed.
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Old 12-10-2008, 10:38 PM   #5
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Re: How to check gear ratio without removing diff cover?

But a posi will rotate both and on an open....Only 1 will turn the driveshaft so.....

I've never had a problem turning just 1 tire. I generally use the passenger side, since it is always "locked".

Besides...Who ca reach both tires at the same tire & rotate them?

Last edited by Stephen; 12-10-2008 at 10:42 PM.
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Old 12-11-2008, 08:02 AM   #6
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Re: How to check gear ratio without removing diff cover?

So basically rotate the wheel one full turn and count the number of revolutions of the driveshaft?
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Old 12-11-2008, 08:22 AM   #7
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Re: How to check gear ratio without removing diff cover?

Quote:
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So basically rotate the wheel one full turn and count the number of revolutions of the driveshaft?
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Old 12-11-2008, 04:33 PM   #8
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Re: How to check gear ratio without removing diff cover?

Quote:
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So basically rotate the wheel one full turn and count the number of revolutions of the driveshaft?
Both wheels in the same direction as Stephen 87 iroc already said.
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Old 12-11-2008, 05:55 PM   #9
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Re: How to check gear ratio without removing diff cover?

To be absolutely sure, take the cover off and look at the numbers on the ring and pinion for pete's sake--the fluid has probably never be changed anyway.

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Old 12-12-2008, 07:34 AM   #10
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Re: How to check gear ratio without removing diff cover?

If you have a good working posi and both wheels turn together then you can turn one wheel. If the posi slips any at all while you are doing this then your calculations will be way off. This is best done by 2 people so that someone can keep an eye on each wheel. If you have a standard differential then leave one wheel on the ground and turn the other one exactly 2 full turns. This will give you the correct gear ratio.

Turn the wheel and count the drive shaft revolutions. If the drive shaft turns just over 3 turns then it is a 3.08. If it turns almost 3 1/2 times then it is a 3.42. If it turns about 3 1/4 times then it is a 3.23. 3 3/4 is a 3.73...
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Old 12-12-2008, 09:52 AM   #11
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Re: How to check gear ratio without removing diff cover?

This is about as accurate as any of the other methods, except for taking off the cover and looking....

Guess what ratio you have. Plug it into a google calculator.
INPUT: Tire size, Wheel size, RPM, transmission gear ratios, Speed (MPH or KM/H).

OUTPUT: Rear gear

some of them arent aranged input output like that, so you put in what you think you have, and see if the speed and revs match. Faster you go, the more accurate it is... But thats relative.
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Old 12-13-2008, 12:04 PM   #12
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Re: How to check gear ratio without removing diff cover?

Pull the cover off and count the teeth or get the ratio numbers off the side of the ring gear. Replace the oil while you're at it. It probably hasn't been changed for a while.
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