Speedometer gears include both the drive gear and the driven gear. The drive gear refers to the gear that is on a transmission’s output shaft. The driven gear is located in a removable housing, usually in the tailhousing, of transmissions. Be aware that some transmissions will have different driven gear housings depending on the tooth count of the driven gear. TCI stocks popular speedometer gears for GM and Ford transmissions. The following formula will work for any GM or Ford vehicle and is very useful when there is no established baseline from which to work, such as replacing a transmission in a vehicle that was purchased without a driveline.
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