73-87 Chevy _ GMC Trucks > Instrumentation

Factory speedo gears?

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Scaryfastatx:
Question for you all

Did the factory use a fixed set of speedo gear combos on these trucks?

Is there a resource on what the factory used for certain equipment?

My speedo is showing about ~35mph when I'm doing ~22mph

I don't have a tach, so just trying to research what came in these to get an idea while I wait to get a tach to see what my engine speed is compared to my velocity

Thanks!

zieg85:
There are 3 things, the drive gear on the output shaft, driven gear in the housing that the speedometer cable attaches to and possible another adaptor that does fine adjustments if the combination isn't just perfect.  Attached is an example of what is found in the GM manuals

Mr Diesel:
These speedometers are based on a magnet system that inevitably deteriorates with age, causing inaccuracy. Best way to get your speedometer accurate is buy several different gears for the tranny side and experiment with each, using your phone GPS to check each one for accuracy.

JohnnyPopper:
That's great advice Mr. D.

I looked at the chart saying drive and driven gears. Drive is obviously on the output shaft and driven on the end of the speedo cable. Where does the 'adapter' come in? Sorry to sound so clueless... :-[

Scaryfastatx:

--- Quote from: zieg85 on November 23, 2023, 05:04:54 PM ---There are 3 things, the drive gear on the output shaft, driven gear in the housing that the speedometer cable attaches to and possible another adaptor that does fine adjustments if the combination isn't just perfect.  Attached is an example of what is found in the GM manuals

--- End quote ---

Cool thanks, so my truck had factory cruise control, but I bypassed it and went direct, would that cause a problem? I figured it would be 1:1 thru that cruise control box

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