speedometer trouble

[alhem]

On my Bonneville SE_90 the speedometer suddenly has started behaving crazy...
When standing still the needle goes beyond full speed and when driving it backs down to about 125 kmph= about70mph. When I drive real slow I can hear a weak, hissing sound from the instrumentcluster!?!
Ideas,anyone?

[sixsmiles]

Hissing sound is most likely a vacuum hose either disconnected or split usually related to the heat and AC system.
The Speedometer is most likely a speed sensor, or ground problem.
Good luck.

[alhem]

No, the hissing sound stops as soon as the car stops and starts again as soon as the car begins to roll. It is not related to rpm but to the moving car.