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post #2 of (permalink) Old 05-26-2005, 08:37 AM
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Re: T-19 first gear ratio identification

Division and multiplication. Start at the front. Count the number of teeth on the input gear. Divide that into the number of teeth on the gear it drives, and save that number. It will probably be around 1.5.

Then go to the output - the last driven gear with the transmission in first - and count the teeth. Divide that number by the number of teeth that drive it. Multiply that by the first number you got, and the result will be the ratio in that gear.

Once you have the transmission ratio, you can do the same thing to get the transfer case ratio and the axle ratio. Then multiply all three together and you have your crawl ratio.

If the gear train is assembled so that you can't count teeth, tape a string to the shaft that turns more, and then turn the other shaft exactly one turn. By counting the wraps of string plus the fraction of a full turn on the other shaft you can get a pretty good estimate of the ratio.

You will almost never encounter an even-number ratio, like 72/18 (4:1) because in that case the same teeth would engage each other with every turn, causing uneven wear. When the ratio is a number like 74/18 (4.11111... :1) every driven tooth will eventually engage every drive tooth.

And welcome to the board!
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