One speed signal for both odo and speedo.
The 140 chassis originally had a mechanical odometer but all replacement inst clusters now have digital odometers. The speedo is adjustable internally on a bench. An input is fed the device to make 60mph (don't know the speed in km) using a signal generator and the signal frequency given by the calibration constant on the back of the instrument, K=xxxx. If you have the right odometer as you say, the speedo just needs recalibration by a speedo shop.
Bosch Master, ASE Master, L1
33 years MB technician