Speedometer playing up

[Cabgirl]

Just noticed that I've not been driving my car for a while and that the speedometer is not working probably. It shows my speed until the auto changes gears or if I break and then accelerate.

Can anyone tell me what is wrong with it?

Cheers
Cabgirl

[SPADGE]

Dodgy connection at the speed sensor in the diff.
Cut off approx 300mm of the wire and plug and replace it.

[midnight]

if its not the plug or the wire it will be something wrong with the clocks or the pulse generator(the thing on the back of the diff which the speedo wires connect too