Speedometer gear usage

This information was taken from a 1970 Oldsmobile shop manual
Note 1: All manual transmissions use a 8 tooth drive gear (The one on the transmission output shaft)
Note 2: Both the Turbo-350 and Turbo-400 transmissions use a 18 tooth drive gear
2.56 Base 3 spd. ("A" body) (M14 Transmission) (M-20 and M-21) Drive gear is 18 tooth
RATIO 3 Speed (Column) 3 Speed (Floor) 4 Speed Automatic
Tire Size Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter
H-78                   34 lt. Grn None
855-14                   34 lt. Grn None
F-78                   35 orange None
G-78                   35 orange None
G-70                   35 orange None
825-14                   35 orange None
                         
2.78 Base 3 spd. ("A" body) (M14 Transmission) (M-20 and M-21) Drive gear is 18 tooth
RATIO 3 Speed (Column) 3 Speed (Floor) 4 Speed Automatic
Tire Size Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter
H-78 20 Blue 1.202 21 Red 1.272       37 Red None
855-14 18 Brown 1.125 18 Brown 1.132       36 White None
F-78 17 Purple None 17 Purple none       38 Blue None
G-78 17 Purple None 17 Purple none       38 Blue None
G-70 17 Purple None 17 Purple none       39 Brown None
825-14 17 Purple None 17 Purple none       38 Blue None
                         
3.08 Base 3 spd. ("A" body) (M14 Transmission) (M-20 and M-21) Drive gear is 18 tooth
RATIO 3 Speed (Column) 3 Speed (Floor) 4 Speed Automatic
Tire Size Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter
H-78 18 Brown none 18 brown none 18 brown none 43 purple none
855-14 18 Brown none 18 brown none 18 brown none 40 black none
F-78 19 natural none 19 natural none 19 natural none 42 green none
G-78 21 red 1.125 21 red 1.132 21 red 1.132 42 green none
G-70 19 natural none 19 natural none 19 natural none 43 purple none
825-14 21 red 1.125 21 red 1.132 21 red 1.132 42 green none
                         
3.23 Base 3 spd. ("A" body) (M14 Transmission) (M-20 and M-21) Drive gear is 18 tooth
RATIO 3 Speed (Column) 3 Speed (Floor) 4 Speed Automatic
Tire Size Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter
H-78 19 natural none 19 natural none 19 natural none 43 purple none
855-14 19 natural none 19 natural none 19 natural none 42 green none
F-78 20 blue none 20 blue none 20 blue none 45 lt blue none
G-78 17 purple .8653 17 purple .866 17 purple .866 44 dk grey none
G-70 20 blue none 20 blue none 20 blue none 45 lt blue none
825-14 19 natural none 19 natural none 19 natural none 44 dk grey none
                         
3.42 Base 3 spd. ("A" body) (M14 Transmission) (M-20 and M-21) Drive gear is 18 tooth
RATIO 3 Speed (Column) 3 Speed (Floor) 4 Speed Automatic
Tire Size Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter
H-78 20 blue none 20 blue none 20 blue none 45 lt blue none
855-14 20 blue none 20 blue none 20 blue none 45 lt blue none
F-78 21 red none 21 red none 21 red none 34 lt green .7222
G-78 18 brown .8653 18 brown .866 21 red none 34 lt green .7333
G-70 21 red none 21 red none 21 red none 41 yellow .8655
825-14 21 red none 21 red none 18 brown .866 40 black .8653
                         
3.91 Base 3 spd. ("A" body) (M14 Transmission) (M-20 and M-21) Drive gear is 18 tooth
RATIO 3 Speed (Column) 3 Speed (Floor) 4 Speed Automatic
Tire Size Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter
H-78 17 purple .7333 17 purple .7330 20 blue .866 40 black .7692
855-14 20 blue .8653 20 blue .8660 18 brown .785 44 dk grey .8653
F-78 21 red .8653 21 red .8660 21 red .866 39 brown .7222
G-78 17 purple .7222 17 purple .7330 17 purple .733 37 red .6944
G-70 21 red .8653 21 red .8660 21 red .866 40 black .7333
825-14 17 purple .7222 17 purple .7330 20 blue .866 39 brown .7333
                         
4.33 Base 3 spd. ("A" body) (M14 Transmission) (M-20 and M-21) Drive gear is 18 tooth
RATIO 3 Speed (Column) 3 Speed (Floor) 4 Speed Automatic
Tire Size Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter
H-78 19 natural .7333 19 natural .7330 20 blue .785 40 black .6944
855-14 18 brown .7222 20 blue .7850 20 blue .785 35 orange .619
F-78 19 natural .7222 18 brown .6660 21 red .785 37 red .619
G-78 19 natural .7222 19 natural .7330 21 red .785 41 yellow .6944
G-70 19 natural .7222 21 red .7850 21 red .785 37 red .619
825-14 19 natural .7333 19 natural .7330 19 natural .7333 45 lt blue .7692
                         
4.66 Base 3 spd. ("A" body) (M14 Transmission) (M-20 and M-21) Drive gear is 18 tooth
RATIO 3 Speed (Column) 3 Speed (Floor) 4 Speed Automatic
Tire Size Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter
H-78 17 purple .619 20 blue .7330 20 blue .733 43 purple .6944
855-14 20 blue .7333 20 blue .7330 21 red .785 44 dk grey .7222
F-78 21 red .7222 21 red .7330 21 red .733 40 black .619
G-78 20 blue .7222 19 natural .6660 21 red .733 39 brown .619
G-70 21 red .7333 21 red .7330 21 red .733 40 black .619
825-14 20 blue .7222 19 natural .6660 19 natural .666 39 brown .619
                         
5.00 Base 3 spd. ("A" body) (M14 Transmission) (M-20 and M-21) Drive gear is 18 tooth
RATIO 3 Speed (Column) 3 Speed (Floor) 4 Speed Automatic
Tire Size Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter Teeth Color Adapter
H-78 18 brown .619 20 blue .6660 20 blue .666 41 yellow .619
855-14 18 brown .619 21 red .6660 21 red .733 45 lt blue .6944
F-78 19 natural .619 21 red .6660 21 red .666 43 purple .619
G-78 21 red .6944 20 blue .6660 20 blue .666 42 green .619
G-70 19 natural .619 20 blue .6660 20 blue .666 43 purple .619
825-14 21 red .6944 20 blue .6660 20 blue .666 42 green .619
                         
                         
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Last Updated on 12/21/99
By Fred Teufert
Email: fteufert1@worldnet.att.net