Joe in Canada Posted March 24, 2015 Share Posted March 24, 2015 I changed the gear ratio from 4.75 to 3.6 in a 1930 Cadillac does anyone know to adjust the speedometer or parts to get the proper reading of my speed??? Thanks Joe Link to comment Share on other sites More sharing options...
Ron Lawson Posted March 24, 2015 Share Posted March 24, 2015 Usually you have to change the speedo drive gears in the transmission Link to comment Share on other sites More sharing options...
Joe in Canada Posted March 24, 2015 Author Share Posted March 24, 2015 Thanks Ron does anyone know a source for the speedo drive gears in the transmission. Thanks Joe Link to comment Share on other sites More sharing options...
The Old Guy Posted March 24, 2015 Share Posted March 24, 2015 Check with a trans shop that works on trucks !! They have units that fit on your trans gears,(where the cable hooks up ) that have all different ratios. Link to comment Share on other sites More sharing options...
JACK M Posted March 24, 2015 Share Posted March 24, 2015 Check with a trans shop that works on trucks !! They have units that fit on your trans gears,(where the cable hooks up ) that have all different ratios.Yes, a good speed shop can fix you up. Link to comment Share on other sites More sharing options...
Rusty_OToole Posted March 24, 2015 Share Posted March 24, 2015 These days I believe it is a simple matter to time your speedo and odometer using the GPS or GPS function in a cell phone or tablet.It is customary to drive at 60 MPH and note what the speedo reading is.Once you have that information it is possible to adjust the speedo accordingly, by changing the drive gear in the transmission. Link to comment Share on other sites More sharing options...
jvelde Posted March 24, 2015 Share Posted March 24, 2015 On a related note, the odometer on my car seems to track pretty close to the mile markers, but the speedo at 60 reads 75 or so. I have thought about changing the gear on the trans but worry about screwing up the odometer accuracy...thoughts? Link to comment Share on other sites More sharing options...
Rusty_OToole Posted March 24, 2015 Share Posted March 24, 2015 Some speedos are accurate at 30 but off at 60 or vice versa. Others give accurate mileage but inaccurate speed. You could check both speedo and odo with the GPS trick and if they are way off each other, and it bothers you, it may be necessary to have the speedo rebuilt. Link to comment Share on other sites More sharing options...
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