I am about to install the correct powerglide in my 63. Is there a way to figure out the correct gear to use in the trans. for the speedometer? I hate to do it by trial and error. The rear end is a 308 the tires are 205 75R 15. Any assistance is appreciated.
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Re: Speedo gear
i believe chevy still services the driven gear you need for a 3.08;1 rear ration. mike -
Re: Speedo gear
Bob-----
There are formulas to calculate the required speedometer drive gear. However, in this case, I don't think that they are going to be necessary. Your 205-75-15 tires are very close to the original tires in OD (and revolutions/mile). The difference between them is so slight that the original speedometer gear used for your application should work within an acceptable degree of speedometer accuracy. In fact, since speedometer gears are only available in a limited range of tooth counts, there isn't an available gear that would give you any better accuracy than the stock gear. The gear you need is a 20 tooth blue gear of GM #3987920 which is still available from GM.
You don't need to worry about the drive gear since Powerglides were only used with the drive gear compatible with the above-referenced driven gear. Of course, if this transmission was previously modified for use with a numerically high ratio rear gear, then you may need to consider the drive gear. I doubt it, though.In Appreciation of John HinckleyComment
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Re: Speedo gear
I used the information on this site when I changed the speedo gear from 20 teeth to 22 teeth to compensate for P215 tires. A true 100kph (62mph) as recorded by a friend's C5 was showing as 70mph on my speedo. With the 22-tooth gear 100kph is now showing 62mph on my speedo. Bang on! BTW Canada is metric; hence the C5 kph.
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Re: Speedo gear
Thanks for the info. As usual Joe Lucia is amazing with his part numbers.Comment
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