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My speedometer is reading 18% higher than I am traveling. For example, when it reads 55, I am, traveling at 45. I have 18 teeth on the cable. How many teeth should I have for an accurate reading? Thnaks.
55 divided by 45 is 1.22222. Taking 1.2222 times 18 gives 22, so you need a 22-toothed gear. Unfortunately, as shown here, that's not a stock Ford gear. But, I have seen them at places like Summit.
Thanks Gary. Now I understand the math. I bet it is a 21 as the truck is all original except for the trans rebuild. I was looking at speedometer while passing the local radara, so I could be off a mile or two and that is if those are calibrated correctly.
55 divided by 45 is 1.22222. Taking 1.2222 times 18 gives 22, so you need a 22-toothed gear. Unfortunately, as shown here, that's not a stock Ford gear. But, I have seen them at places like Summit.
But, a readily-available 21 would get you close.
22 tooth gear will read too fast, so will a 21 tooth gear.
The nylon DRIVEN gears at the end of the cable are approx. 5 MPH difference, so the OP needs a 20T gear to slow the speedo down from 55 to 45 MPH
The same 16 thru 21 tooth nylon DRIVEN gears have been used from 1960, are available from Ford and auto parts stores.
Bill - You need some qualifier in there as the same gear change that would make a 5 MPH difference at 30 MPH would make a 10 MPH difference at 60 and a 15 MPH difference at 90 MPH.
Just FYI, here's a table for the driven gears for this particular situation. It is just simple math. The yellow represents the information given, that at 45 MPH actual the speedo is reading 55 MPH.
That chart sure is helpful [motivation wise]. I have a speedo discrepancy myself that I've been meaning to address. Maybe this will get me to actually check it out...
Just FYI, here's a table for the driven gears for this particular situation. It is just simple math. The yellow represents the information given, that at 45 MPH actual the speedo is reading 55 MPH.
Thanks Gary, I am spot on now. I just need to remember that it is correct when reading it.
