1.9 speedometer

[D R Oldfield]

Hi the 1.9 1996 z3 i have just bought seems to have a very erratic speedometer were do they get the signal from to sense the speed ? do they still use a cable or is it done electronically ? if i change the clock assembly how would i go about getting the mileage to be correct on the new speedo ?
thanks

 

[NZ00Z3]

The speedo sensor is on the back of the diff. It is an electric system.

1) Check that the plug is clean and correctly fitted into the diff.

2) You can test the speedo with the instrument cluster hidden tests. See this link. https://www.bimmerforums.com/forum/showthread.php?736153-Test-Mode-Hidden-Codes-in-your-car!

3) If 1 and 2 above check out OK, then is could be a wiring issue or the instrument cluster itself.