The two easiest things to do are clean & lube as Jerry recommends and not over tighten the connection as the speedometer as Wally noted. Either or both of those can make the needle bounce. My experience has been that a lube issue usually presents as chattering as well as bouncing. While I've not personally experienced it, I've been told by a speeo rebuilder that a worn/damaged drive gear can produce bounce as well.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.