Speedo Drive Gear Colours

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Page created by MRHZV8 Feb 17th 2005:

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M20, M21 and M40 Speedo Driven Gears. Click to Enlargen. Photo by Dusty Dirt Roads.

Speedo Gears:

The number of Teeth on the2 Speedo Gears determines the accuracy of the Speedo. Variables are the Diff Ratio and the Tyre Size. An increase in Tyre Size (195x75 - 195x85) needs a increase in the Speedo Gears Ratio to match the increase in Road Speed. This means using a smaller Driven Gear. An increase in Diff Ratio (3.06:1 - 3.36:1) needs a decrease in the Speedo Gears Ratio to match the decrease in Road Speed. This means using a larger Driven Gear.

Speedo Drive Gear Colours:

The colour of the Drive Gear determines the number of Teeth it has.

Drive Gear Colour M20 M21 & M40 Drive Gear Teeth M20 M21 & M40
Yellow 10
Blue 9
White 8
Brown 7
Drive Gear Colour M41
Drive Gear Teeth M41
Steel Blue 17
Drive Gear Colour M6 Drive Gear Teeth M6
Brown 7

 

Speedo Driven Gear Colours:

The colour of the Driven Gear determines the number of Teeth it has.

Driven Gear Colour M20 M21 & M40 Driven Gear Teeth M20 M21 & M40
 Dark Blue  22
 Green  21
 White  20
 Pink  19
 Red  18

 

Gearboxes:

 

Gearbox Model Name Description
M6 4 Speed Torquemaster Phillipino
M20
Aussie 4spd Manual
M21 Aussie 4spd Close Ratio Manual
M40 Trimatic
M41 TH400

 

Tyre Option:

Tyre Option Description
QCR  CR78S14
QCJ CR70H14
QBC  BR760H15

 

Selecting the Right Speedo Gears:

Submission by Campbell Sept 29th 2008: In order to select the right speedo gears in an Aussie or Trimatic box;
1. Go HERE, select metric, punch in your rear tyre specs and find your tyre's circumference.
2. Take this figure and divide by 1000(to obtain reading in metres).
3. Divide 1666.7 by the figure you ended up with in step 2. This will give you your rear wheel rpm@100kph.
4. Multiply your(@100kph)rear wheel rpm by your diff ratio(eg:3.08 if 3.08:1), to obtain g/box output shaft speed@100kph.
5. Divide 1042(desired cable rpm@100kph)by your g/box output shaft speed. This will give you the ratio needed to correctly calibrate your speedo.
6. Check the list for the closest ratio match. A higher number will see your speedo too fast. A lower number will see it too slow. So IMHO if the exact match can't be achieved. It is best to select the next highest gear combo.
Cheers. End of submission by Campbell.

M20, M21 and M40 Speedo Driven Gears. Click to Enlargen. Photo by FJ53.
M20, M21 and M40 Speedo Driven Gears. Click to Enlargen.
M20, M21 and M40 Speedo Driven Gears. Speedo Driven Gears. Suit trimatic , 3sp and 4 speed boxs ht and later. Click to Enlargen. Photo by HRAmbo. Info by Holden Owner
M20, M21 and M40 Speedo Driven Gears. Speedo Gear Colour Chart. Click to Enlargen. Image by Campbell.

Speedo Gear Chart:

 

Diff Ratio Transmission Drive Gear Colour Driven Gear Colour
Tyre Option Tyre Option Tyre Option Tyre Option Tyre Option
G70 2.60:1 M41 17 Teeth Steel Blue Red 37 Teeth QBC QCV QCH  ZCH  
GU7 2.78:1 M40 & L6 8 Teeth White Pink 19 QBC        
GU7 2.78:1 M40 & L6 8 Teeth White Brown 18 Teeth QCJ QCR XCR ZCH  
GU7 2.78:1 M40 & V8
9 Teeth Blue
Green 21 Teeth  QBC        
GU7 2.78:1 M40 & V8 9 Teeth Blue White 20 Teeth QCJ QCH XCH  ZCH  
GU4 3.08:1  MC6   7 Teeth Brown  Red 16
 QBC  QCJ  QCR  XCR  ZCH
GU4 3.08:1  M40 &M20
 8 Teeth White  Green 21 Teeth
 QBC        
GU4 3.08:1  M40 &M20
 8 Teeth White  White 20 Teeth
 QCJ  QCR  XCR  ZCR  
GU4 3.08:1  M41  17 Teeth Steel Blue  Purple 43 Teeth
 QBC  QCJ  QCR  XCH  ZCH
 GU4  3.08:1  M20
  8 Teeth White   Green 21 Teeth  QBC        
 GU4  3.08:1  M21
  8 Teeth White   White 20 Teeth  QCJ  QCH  XCH  ZCH  
GU4 3.08:1  M40  9 Teeth Blue  Red 23 Teeth
 QBC  QCJ  QCH  XCH  ZCH
GV4 3.36:1  M20 & M40
 8 Teeth White  Dark Blue 22 Teeth
 QBC  QCJ  QCR  XCR  ZCR
GV4 3.36:1  M21
 8 Teeth White  Dark Blue 22 Teeth
 QBC  QCJ  QCH  XCH  ZCH
GV4 3.36:1  MC6
 7 Teeth Brown
 Blue 20 Teeth
 QBC        
GV4 3.36:1  MC6
 7 Teeth Brown
 Yellow 19 Teeth
 QCJ  QCH  XCH  ZCH  
GV7 3.55:1 M20  8 Teeth White  Yellow 24 Teeth QBC
QCR      
GV7 3.55:1 M20  8 Teeth White  Red 23 Teeth
QCJ  QCR  XCR  ZCR  

 

The EJ Holden came only with one gear drive and its white in the manual cheers Lindsay. This also may be of some interest to you all. Basic and often mis-understood concepts:
A 'tall' diff is a smaller number eg: 2.60 ratio,
a 'short' diff is a larger number eg: 3.90 ratio. Tall diff = longer legs, higher top speed, less RPM at cruise, slower off the line.
Short diff = shorter legs, lower top speed, more RPM at cruise, quicker off the mark. Different diff ratios with 205/60/13 rear tyres:
2.60 = 41.8 Km/h/1000RPM or 2390RPM @ 100 Km/h
2.78 = 39.1 Km/h/1000RPM or 2560RPM @ 100 Km/h
3.08 = 35.3 Km/h/1000RPM or 2830RPM @ 100 Km/h
3.36 = 32.3 Km/h/1000RPM or 3100RPM @ 100 Km/h
3.55 = 30.6 Km/h/1000RPM or 3270RPM @ 100 Km/h
3.90 = 27.8 Km/h/1000RPM or 3600RPM @ 100 Km/h Speedo drive gears
For 13" wheels:
2.60 diff Pink 19 teeth
2.78 diff White 20 teeth
3.08 diff Dark Blue 22 teeth
3.36 diff Red 23 teeth
3.55 diff Yellow 24 teeth
3.90 diff Light blue 25 teeth For 14" wheels:
2.78 diff Pink 19 teeth
3.08 diff White 20 teeth
3.36 diff Green 21 teeth
3.55 diff Red 23 teeth
3.90 diff Yellow 24 teeth The above are all varied again by tyre and wheel sizes.
A 205/60/13 tyre with a 2.78 diff is about the same overall gearing as
a 275/55/17 tyre with a 3.55 diff.

Links:

Speedo Drive, Driven Gears And Cables

Terms:

Terms

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