604 L4-2304cc 2.3L DSL XD-2 (1983)
-
Before accepting complaints for apparent incorrect speedometer readings, verify the complaint over a measured distance. Drive the vehicle
between the measured mile markers that are visible on all major highways.
First verify that the odometer really reads a measured mile (or within plus 3 +/- 2%) for the distance.
Example :
For a true measured 10 miles the odometer should register a reading of 10.0 to 10.5 miles. Thus if the readings are not
within the tolerances, this will indicate if you have incorrect pinion ratios or not.
Secondly, to verify speedometer needle accuracy, remember that at a constant speed of 50 MPH it takes 72 seconds to travel one mile. To
accurately know the true speed over a measured mile, for any time taken, while maintaining a constant speed, use the following simple formula :
Thus if you take a stop watch and a pocket calculator with you, you can easily and accurately compare actual speedo readings against true measured
speed.
-
Speedometers are calibrated to read fast. 5% is totally acceptable. If speedo error is excessive then it is better to have the speedo head
calibrated by an instrument shop to between 1 and 3% fast rather than exchange it, as the replacement head may be calibrated the same as the
original unit.
