Part Numbers and Combinations for Rear-End Gears
Q: I want to buy speedometer drive/driven gears, what are the part numbers and combinations?
A: Here is a list of GM part numbers for drive and driven speedometer gears, as well as some combinations that are known to work:
Part No. Teeth Color Sleeve* 25513042 35 Orange 25007338 25513043 36 White 25007338 25513044 37 Red 25007338 25513045 38 Blue 25007338 25513046 39 Brown 25007338 25513047 40 Black 25007339 25513048 41 Yello 25007339 25513049 42 Green 25007339 25513050 43 Purple 25007339 25513051 44 Dk Gray 25007339 25513052 45 Lt Blue 25007339
*Some applications may use Sleeve No. 25007224 or 10456092 in place of 25007338, or 25007308 or 1045089 in place of 25007339. Red Drive Gear Combinations
With drive gear number 8640517, (red, 17 teeth) the following combinations apply:
Axle Tire Dia. Driven Gear Ratio (Nominal) (Tooth Count) 2.59 26.0 35 25.7 36 2.73 26.0 37 25.7 38 2.87 26.0 39 3.07 26.0 42 3.31 26.0 45
Gray Drive Gear Combinations With drive gear number 8642620, (gray, 15 teeth) the following combinations apply:
Axle Tire Dia. Driven Gear Ratio (Nominal) (Tooth Count) 3.33 25.7 40 3.45 25.7 41 3.54 26.0 42 25.7 43
Lower ratio (higher numerically) rear or smaller diameter tire requires higher driven gear tooth count. Increasing or decreasing driven gear tooth count by one will usually accommodate a 1/4" to 1/2" change in tire diameter.