I am contemplating building a custom instrument cluster for my '50 Ford truck. I want to use OEM GM components. Here's my question: If I use a mechanical GM speedometer in place of the original Ford unit, will the GM speedo read the same speed as the original? I'm aware that I may have to change the cable to mate to the GM speedo, but I'm curious as to whether the two speedometers are calibrated the same. I know about the need to calibrate a speedometer in relation to gear ratio and tire size. My concern is if the two speedometer heads would read the same if you just swapped them at the cable. I hope I'm making sense here!
If they both measure 55 MPH at the gauge, wouldn't the speedometer gear at the transmission make all the difference, not the actual gauge itself? ~Jason
Basicaly yes no problem. The US has for many years used a standard of 1000 cable revs will equal 1 mile. If the 1000 revs are done in one minute the speedo will read 60 MPH.
The Jalopy Journal
