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Old 07-26-2004, 02:18 AM
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Driven, drive gear info

Can anyone tell me the different gears I will need (driven / drive) for the speedo on a TH350 from 84 that came with a 231(as I understand it they installed different drive gears from the factory in different 350s) if I'm going from the stock 2.41:1 to 3.23:1 gears? How many teeth for each? I havent even looked to see how many teeth is on the driven gear yet, thanks.
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Old 07-26-2004, 08:43 AM
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gears

I can if you give me the rear tire diameter.

Keith
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Old 07-26-2004, 03:14 PM
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Oh yeah, duh, 25.85"
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Old 07-26-2004, 07:25 PM
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Quote:
Originally posted by 87442lover
Oh yeah, duh, 25.85"

STILL need the driver gear number.....

There are 8 different drive gears

7
8
9
10
17
18
19
20

and 17 driven sets

18,19,20,21 and 22

34,35,36,37,38,39,40,41,42,43,44 and 45

You can tell what the number is by the color of the gear.


Formula for speedo correction.

The speedometer cable must turn 1000 Revs in 1 mile.

tire height 25.85 X 3.1417 (pie) =81.21

A mile is 5280 Feet so X 12" is 63360 inches

63360" divided by 81.21" =780.2

Your tire turn 780.2 times in a mile

Your gear ratio is 3.23 so 780.2 X 3.23 = 2520

Your driveshaft turns 2520 times in a mile.

The cable needs to turn 1000 times so......... 2520 divided by 1000 is 2.52

The ratio between the driver/driven must be 2.52

EXAMPLE............if you driver gear is 8

8T X 2.52 = 20.16 or a 20T driven and you will be corrrect


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Old 07-27-2004, 02:01 AM
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Take your tire diameter & gear ratio to www.novasource.org/speedo.htm & plug it into the formula in the text to get the speedo gear ratio needed, then look at the charts to see what combination comes closest to what you need.

You can work the chart backwards to see what drive gear you have by counting the teeth on your old driven gear.

There are rev/mile & tire diameter calculators at http://tciauto.com/tech_info/speedo_gears.htm
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Old 07-27-2004, 08:11 AM
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Some of the gear counts listed by Deuce are for a BOP tail housing. They do not directly interchange with a chevy style speed-O.

The drive gears ..... 17 teeth on up or for a Buick / Olds style. The diameters are different .

Same for the driven gears 34 teeth & up
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