Speedo calibration?

[hopped up]

So I put in the new speedo cable in my 64 c10, 350/350 stock gauges. The speedo is off, what do I need to calibrate it to read the right speed. I have L78 whitewalls all around. Not sure how tall they are. Thanks for any input
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[protrash64]

My '66 is the same. It's reading about ten mph fast. I believe you need to change the gears in the trans or get some type of adapter set-up. I havent done it hopped, so I'm not exactly sure.

Or just keep getting different size back tires until it reads right!

[Rich 5150 69]

Try here http://2004r.com/speedoCalc/speedocalc.shtml

[fleetsidelarry]

first figure out how much off your speedo is. you need to compare your actual speed to your indicated speed. there are several ways to do this: the old fashion way by timing how fast you traverse a known distance (typically a measured mile); using a calculator as suggested above (you need a tachometer for this method), or; use a GPS (or GPS App on a smart phone)

Then, on the side of the transmission where the cable attaches is a gear housing, take the cable off and remove the housing, which holds the driven gear. that gear will be colored and have a tooth count on it.

finally, call these guys and tell them what you have:
http://www.transmissioncenter.net/sp...n_______va.htm

[Slow Build]

I'll have to look into this too. Mines a little off.

[hopped up]

That's exactly what my speedo looks when I'm on the fwy!
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[fleetsidelarry]

actually, Rich, that looks about right for a 700r4/3.73. what do you have?

[Slow Build]

Originally Posted by fleetsidelarry

actually, Rich, that looks about right for a 700r4/3.73. what do you have?

TH350 with unknown gear ratio. I was probably doing 70 MPH.
If I was actually going that fast my truck would probably look like a satellite re-entering the atmosphere, flaming parts flying all over the place.

[fleetsidelarry]

Originally Posted by Slow Build

If I was actually going that fast my truck would probably look like a satellite re-entering the atmosphere, flaming parts flying all over the place.

yeah, mine too.

just guessing on tire size, but 70 is about right if your truck has a 3.73. if the vehicle the tranny came out of had a 2.73 (or maybe a 3.08, depending on original tire size) you would be seeing that sort of difference.

you and hopped up may have to swap out both speedo gears, (driven AND drive)

[protrash64]

.........looks like my dash, too. 3k rpm.

[hopped up]

wtf! now my speedo started to click and stays between 50-60. and my odometer just stopped working completely!
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