Ford cummins tranny issues
#12
I'm not sure if ford used a transmission driven speedo or the electronic sensor in the rear diff like the later models. If its the electronic style then get a superlift truspeed module. It allowes you to set the speedo for different tires and gears. If its the mechanical style, then you will need to pull the driven gear and count teeth and look at the colors. different colors had different ratios for trans and diff options. You might still be able to get the speedo gears from ford or possibly a good tranny shop. Hope this helps.
#13
#15
You actually need to measure the height of your tires. Very rarely are the tires true to the size printed on the sidewall. Most 35's are only about 33 1/2" to 34" tall. Then do the math. If I remember the formula correctly it should be mph x trans ratio x axle ratio x 336 divided by tire size. In 4th (direct) with 3.55 and 34's at 65 mph, you would be turnin about 2300 rpm. If you want to know what the rpms are for 5th(overdrive), just put that gear ratio in. The numbers wont lie but tachs and speedos often do! Good luck.
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