Speedo Gears

[smokelessfire]

Here is a good resource for fixing your speedometer after a rear end swap or tire change:

http://www.transmissioncenter.net/speedometer_calibration_______va.htm#400

[88hurstolds]

Stock TH2004R with a 3.73 rear end use a 10 tooth drive (governor) gear PN 8639906 (Green) and a 30 tooth driven gear PN 561035 (Blue) with a 26" tire however 29 tooth gear should be used with a 26" tire, PN 403999 (Green).
Why GM chose gears that would make the speedometer read less is beyond me, my guess is to compensate for tire wear since it corresponds to a 25.1" tire???


For a 27" tire use a 28 tooth driven gear PN 410731 (Yellow gear) with the 10 tooth drive gear
For a 28" tire use a 27 tooth driven gear PN 410417 (Black gear) with the 10 tooth drive gear
For a 29" tire use a 26 tooth driven gear PN 25502669 (Brown gear) with the 10 tooth drive gear

For half sizes you will need to change to a 11 tooth drive gear:
26.5" -11/31
27.5" -11/30
28.5" -11/29
29.5" -11/28
30.5" -11/27
31.5" -13 PN 8634934 (White)/31 PN 403417 (White)


For 3.42 rear end ratio you will need an 11 tooth drive gear PN8634965 (Orange) with a 30 tooth driven gear PN 561035 (Blue) for a 26" tire
26.5" -10/26
27" -11/28
27.5" -12 PN 8634935 (Red)/30
28" -11/27
28.5" -12/29
29" -11/27
29.5" -12/28
30" -13/30
30.5" -12/27
31" -13/29
31.5" -13/26



For 3.08 rear end ratio you will need a 13 tooth drive gear PN8634934 (White) and a 31 tooth driven gear PN 403417 (White) with a 26" tire