Shift Rite Transmissions - Speedometer Gears

Drive Gear
Tooth	Color	GM Part #
15	Gray	8642620
17	Red	8640517
18	Blue	8640518
19	Yellow	8640519

Driven Gear
Tooth	Color	GM Part # (Electric)	GM Part # (Cable)
34	Light Green	9774413	25513041
35	Orange	9780387	25513042
36	White	1359270	25513043
37	Red	1359271	25513044
38	Blue	1359272	25513045
39	Brown	1359273	25513046
40	Black	1362048	25513047
41	Yellow	1362195	25513048
42	Green	1362049	25513049
43	Purple	1362196	25513050
44	Dark Grey	9780470	25513051
45	Light Blue	9775187	25513052

To determine your tires true diameter in relation to determining what speedometer gears you need, measure from the ground up to the center of the axle then multiply by two. The actual run out of the tire can be as much as 2 to 3 inches less than what the circumference of the tire measures. In effect your tire has two diameters.

Twelve speedometer driven gears are available for the 700R4 / 4L60 transmissions to calibrate the speedometer with various axle ratios and tire diameters. The number on the driven gear housing must match the number of teeth on the driven gear. Unless driven gears with more than 45 teeth and / or drive gears with fewer than 15 teeth become available, it will be impossible without using a ratio adapter to have an accurate speedometer with rear end gear ratios lower (higher numerically) than 4.10:1, unless 27 inch or larger tires are installed.

With 15 Tooth Drive Gear
Axle Ratio	Tire Height	Driven Gear Teeth
4.56	33	42
4.56	35	39
4.10	26	45 will work, but will read about 3 MPH fast at 50 MPH.
4.10	27	45
4.10	28	44
4.10	29	43
4.10	30	41
4.10	31	40
4.10	33	38
4.10	35	35
3.73	26	43
3.73	27	42
3.73	27 1/2	41
3.73	28	40
3.73	29	39
3.73	30	38
3.73	31	36
With 17 Tooth Drive Gear
Axle Ratio	Tire Height	Driven Gear Teeth
3.73	28	45
3.73	29	44
3.42	26	45
3.42	26 1/2	44
3.42	27	43
3.42	28	42
With 18 Tooth Drive Gear
Axle Ratio	Tire Height	Driven Gear Teeth
3.23	26	45
3.23	26 1/2	44
3.23	27	43
3.23	28	42