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Old 11-17-2004, 04:12 AM   #1
71-longbed
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How to properly correct my speedo

After the rear end ratio change ..
I went from 3.07 to 3.42 .... just recently hooked up a tach and notice my tach says 2500 rpm at 70 mph .. should be sitting at roughly 3,000 rpm....

Suggestions ?

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71 C10 LWB
350sbc -TH350
12 bolt 3.42 Posi



Of all my favorite things to do, The utmost is to have a brew.
My love grows for my foamy friend, with each thirst-quenching elbow bend.
Beer so frosty, smooth, and cold it's paradise pure liquid gold.
Yes beer means many things to me that's all for now cus I gotta pee.
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Old 11-17-2004, 08:18 AM   #2
70c10
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You need the correct plastic gear on the side of the tranny. It's inside the bullet on the end of the cable.
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1970 C/10 Fleetside w/Ghost Flames
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Old 11-19-2004, 01:31 AM   #3
jimfulco
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Count the teeth on the driven gear (the one hooked to the cable). Multiply that number by 3.42 and divide by 3.07. If you're lucky, it will come out a whole number or close enough to round off. Get a new driven gear with that many teeth. If not, you'll need to change the drive gear also (the one on the tailshaft). Go to this site with your tire diameter & you can find what combination to use. http://novaresource.org/speedo.htm

Tire diameter can be calculated here http://tciauto.com/tech_info/speedo_gears.htm
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