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.