speedometer question

[HMP]

On a car, where does the speedometer get its signal from?
More specifically, if you have an older car (let's say 60s/70s), how does it get its information that transfers to the speedometer?

 

[Bailey Boat]

Depending on age it comes either from a cable in the side of the transmission or is read electronically by a sensor....

 

[HMP]

Thank you

 

[Mike Overlay]

A gear ring is on the output shaft of the transmission. On the corresponding housing is a gear drive assembly that has a certain ratio that will spin a cable which then spools up the speed-o.

 

[Mike Overlay]

here is a cut out view of the two gear sets. Green gear on output shaft. Below that is the white gear that spools up the speed-o

 

[rdinatal]

Some transmissions, like my '80 Jeep, you can change out the speedometer pickup assembly to adjust for changes in drive ratio after the transmission (gears or tires). The change was limited in correction ability but cost effective. I was able to compensate for a lower gear change and taller tires.

In the age of 'drive by wire' all that is now accomplished by reprogramming the computer.

 

[Gazengine]

Old VW's beetles drive the speedo from the left front wheel. Square end of cable clips to center of bearing grease cap.