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Reference Manual


Chapter 2: Transmissions: Speedometer Gears


The speedometer cable in a G body is driven by a set of gears in the transmission. A drive gear is connected to the transmission output shaft and turns at the same speed as the driveshaft. A driven gear is installed on the transmission end of the cable and meshes with the drive gear. The gears are choosen to provide a ratio that will rotate the speedometer cable 1000 times per mile. Additionally, a ratio adaptor may be used if a close match can not be made with available gear combinations.


THM200-4R Gears

Drive Color p/n Driven Color p/n

10 teeth Green 8639906 26 teeth Brown 25502669
11 teeth Orange 8634965 27 teeth Black 25524923
12 teeth Red 8634935 28 teeth Yellow 25524921
13 teeth White 8634934 29 teeth Green 25524924
30 teeth Blue 25524925
31 teeth White 403417


THM200C, THM250(C), THM350(C) and THM375B Gears

Drive Color p/n Driven Color p/n

7 teeth Pink 18 teeth Brown 3987918
8 teeth Orange 6261783 19 teeth Natural 3987919
9 teeth Green 6261782 20 teeth Blue 3987920
10 teeth Red or Purple 8261785 21 teeth Red 3987921
17 teeth Red 8628793 22 teeth Gray 3987922
18 teeth Blue 34 teeth Light Green 9774413
19 teeth Yellow 8628891 35 teeth Orange/Pink 9780387
20 teeth Brown 36 teeth White 1359270
37 teeth Red 135971
38 teeth Blue 1359272
39 teeth Brown 1359273
40 teeth Black 1362048
41 teeth Yellow 1362195
42 teeth Green 1362049
43 teeth Purple 1362196
44 teeth Dark Gray 9780470
45 teeth Light Blue 9775187


THM375, THM400, THM700R4 and THM4L60 Gears

Drive Gear Color p/n Driven Color p/n

7 teeth Red 16 teeth (truck)
8 teeth Black 6261783 17 teeth (truck)
15 teeth Brown or Gray 8642620 18 teeth Brown (truck) H
16 teeth Orange 19 Teeth Dark Aqua (truck) J
17 teeth Red 8640517 20 teeth Silver (truck) K
18 teeth Yellow or Blue 8640518 21 teeth Red (truck) L
19 teeth Yellow or White 22 teeth Gold (truck) M
20 teeth Green 23 teeth Maroon (truck)
21 teeth Black 24 teeth Dark Blue (truck)
34 teeth1 Light Green 9774413
35 teeth1 Orange/Pink 9780387
36 teeth1 White 1359270
37 teeth1 Red 135971
38 teeth1 Blue 1359272
39 teeth1 Brown 1359273
40 teeth2 Black 1362048
41 teeth2 Yellow 1362195
42 teeth2 Green 1362049
43 teeth2 Purple 1362196
44 teeth2 Dark Gray 9780470
45 teeth2 Light Blue 9775187
1THM700R4, THM4L60: Use sleeve 25512340
2THM700R4, THM4L60: Use sleeve 25512339


Ratio Adaptors

Marking p/n Ratio

A 3932220 0.7333
C 3950352 0.8241
D 326569 0.9744
H 332537 0.8241
J 3950350 1.3000
K 330192 0.7333
V 3925673 1.1111
W 3925669 0.9444
X 3950348 1.2020
BD 368022 0.9444
BG 368025 1.2020
BH 368026 1.3000



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