speedometer/odometer cut in and out

my speedometer and odometer cut in and out, unpredicable most of the times, one day will start right away and the next wont do it at all. It is the only guage that does this. I have no mods done to the vehicle, any ideas?

I had a connection come lose one time behind the cluster on a Chevy Tracker I had. With that one, when it acted up I just had to wack the top of the dash and it would work again. If that works for you it's the electrical connection behind the cluster.

-Mark