Speedometer drive gear

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Nov 14, 2005 | 11:58 AM

Steve

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Speedometer drive gear

Does anyone know the tooth count on the speedomter drive gear in the '56 three speed lght duty tranny? I am trying to calculate the correct number of teeth on the driven gear I need.

Thnaks guys-
Steve

Nov 14, 2005 | 06:33 PM

barry

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From: Connecticut

There's a few different ones depending on rear end ratio and the tire size you have on your truck. List these and I can look it up.

Barry

50 F-1

Nov 14, 2005 | 06:38 PM

Steve

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Barry-

1956 long bed F-100
Engine 292
axle 3.73:1
Trans light duty column shift 3 speed.
235-75/15 Tire diameter = about 28.5 Inches
Exisiting speedo driven gear has 20 teeth, and speedometer seems to indicate about 5 mph slower than actual.

Steve

Nov 14, 2005 | 07:40 PM

barry

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From: Connecticut

You should have 8 teeth on the driving gear on the tranny output shaft. Your driven gear is the one that makes the difference. It appears you should have a 21 tooth driven gear for 6.50x16 tires or 22 for 6.00x16 inches tires. For 56, there's a 7.10x15 listed, that uses a 19 tooth gear. You're going to have to experiment with the 3 different gears to get a close reading. Being you have modern tires on it, your readings will be slightly off.

Barry

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Nov 14, 2005 | 09:10 PM

hiball3985

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From: tujunga, calif

Barry..just for my curiosity, how do you count teeth on a worm gear(drive gear)???

Nov 15, 2005 | 11:21 AM

barry

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From: Connecticut

That's a good question. I just rely on my parts book for the correct ones. I suppose you could count the high spots.

Barry

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Nov 15, 2005 | 12:43 PM

hiball3985

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From: tujunga, calif

thanks Barry, I only had to change one to get the speedo corrected after changing driven gears didn't work, I remember the one I changed was a differrent color, so I am asuming they are color coded, I know it had what seemed to be more teeth, but I couldn't find a way to count them..LOL