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Speedometer Info

XJ Speedometer Calibration

At the bottom of the speedometer face, look for the numbers 940, 960, 1000, or 1020. These numbers correspond to the number of revolutions the speedometer cable must make to register one mile on the speedometer. Tire size modifications will also require adjustment to your speedometer gearing. In the electronic transducer systems, the speedo transducer will put out 2000 pulses per mile traveled.

To calibrate the speedometer, the appropriate Drive Gear and Driven Gears must be installed in the transmission to provide the speedometer with the proper RPM.

The Drive Gear is a worm gear on the output shaft of the transmission inside the tailpiece. The tailpiece must be removed to replace this gear. But, on most transmissions, it can be viewed by removing the Driven Gear Sleeve. You can count the number of teeth by rotating the output shaft while viewing through the Gear Sleeve hole.

The Driven Gear is easily replaced on most transmissions, even with the transmission in the car. Simply remove the sleeve and slide in a new gear. It is necessary to open up the square output hole in the Driven Gear if Jaguar speedometer cables or connections are used. This can be accomplished with a small square file, or by heating a square rod of the proper size and carefully melting the plastic.

This chart will help you select the proper gears for your transmission. If a certain application shows more than one combination and a Driven Gear is in red print, use that combination for best accuracy. The Jaguar gear ratio for your car can be found on a tag, or stamped into, the differential inspection cover. It will either be the gear ratio, or the number of teeth on the gears inside (obtain the ratio by simple division of the 2 numbers).

On TH-400's, 700-R4's, and "large sleeved" TH-350's there are 3 gear sleeves that hold the "driven" gear. One supports 30-35 teeth, one supports 36-39 teeth, and the last one is for 40-45 teeth. "Caution" gear colors may vary. Use the part number when getting the gear.
 

Rear-End  Gear Ratio  GM TH-350  GM TH-400 or 700-R4 
Drive  Gear  Driven Gear  Drive Gear  Driven Gear 
 3.54 9
Green
GM #6261782
24 
Tan
GM #3860347
17 
Blue
GM #8640518
45
Lt. Blue
GM #9775187
8
Black
GM #6261783
21
Red
GM #398792
44
Dk. Gray
GM #9780470
7 19
Natural
GM #3987919
15
Gray
GM #8642620
40
Black
GM #1362048
18 
Brown
GM #3987918
39
Brown
GM #1359273
 
3.31 10 
Blue
GM #6261785
24 
Tan
GM #3860347
17 
Blue
GM #8640518
43 
Purple
GM #1362196
42
Green
GM #1362049

Green
GM #6261782
22 
Green(Corvette) GM #3860345 Silver
GM #3987922
41 
Yellow
GM #1362195

Black
GM #6261783
20
Blue
GM #3987920
15
Gray
GM #8642620
38 
Blue
GM #1359272
37
Red
GM #1359271
36 
White
GM #1359270
 
3.07  10 
Blue
GM #6261785
23 
Black
GM #3860346
17 
Blue
GM #8640518
40 
Black
GM #1362048
39
Brown
GM #1359273

Green
GM #6261782
21 
Red
GM #3987921
38 
Blue
GM #1359272

Black
GM #6261783
18 
Brown
GM #3987918
15 
Gray
GM #8642620
35
Orange
GM #9780628
34 
Light Green
GM #9774413
 
2.88  10 
Blue
GM #6261785
22
Green(Corvette) GM #3860345 Silver
GM #3987922
17 
Blue
GM #8640518
37 
Red
GM #1359271
21
Red
GM #3987921
36 
White
GM #1359270

Green
GM #6261782
19 
Natural
GM #3987919
15
Gray
GM #8642620
33 
8
Black
GM #6261783
17 
Purple
GM #3987917
32


Note: This table assumes a tire size of 215/70-15 and a speedometer requiring 1000 RPM’s per mile.
Based on data computed by Bruce Bowling, and compiled by Mark Chiampi 9/24/97.

Be advised that this table is a work in progress and while we are making every attempt to check each part number and spec for accuracy, we are only human and do make mistakes. Lump's Admin.

Calculations Table built by Thomas A. Harrison

with Java help from Frank Chu and Louis Reed)

TIRE SIZE DIMENSIONAL DATA, AND

SPEEDOMETER GEAR CALCULATIONS

User Input:

Speedometer Revolutions Per Mile: 

Rear Tire Overall Diameter: 

Differential Gear Ratio: 

Want to find:  Gear 

Drive or Driven Gear teeth (opposite to selected above) 

Click to calculate the gear needed: 

Gear needed 

To reset the form input: 

Size Overall 
Dia.
P205/70R15   26.2
P215/70R15  26.8
P205/65R15  25.5
P215/65R15  26.0
P205/60R15  24.6
P215/60R15  25.2
P225/60R15  25.6
 P205/55R15 23.8
P215/60R16  26.2
P225/60R16  26.6
 P205/55R16 24.9
P225/55R16  25.7

End of Speedometer page.


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