speedometer problems

speedometer isnt working properly
and when it does the needle is jerking up and down
any ideas ?????
Thanks

More info would be helpful.

Model and year?
Manual or Auto?
Car been in any wrecks?
Transmission work recently?

^^^ sounds like someone may have tried replacement gauges and pressed the needles down too hard. I didn't think any newer suby's used a speedo cable into the tranny. I think they use a mag pickup.