The speedometer cable is driven from the gearbox, and curves smoothly up through the engine compartment and the bulkhead to connect with the back of the speedometer.
Speedometer failure is likely to be caused by a fault in the cable that runs from the gearbox to the back of the speedometer gauge.
If the gauge needle does not move at all, the inner cable or drive may be broken; or the cable’s square ends may have become rounded with wear and fail to engage in the sockets.
The fixings at the ends can work loose or be wrongly fitted.
If the gauge needle swings or moves sluggishly, gearbox oil may have seeped up the cable and got into the speedometer itself. In that case, you must replace the speedometer.
If the needle twitches rapidly, see whether the cable is crushed, kinked or too sharply bent. Intermittent twitches can be caused by loose connections or by worn and slipping ends on the cable.
A tapping noise is a sign of a damaged drive or lack of lubrication.
To examine the cable for any of these faults, support the car securely on axle stands or ramps.
Disconnecting and checking the cable