My speedometer

I was heading to work the other day and my speedometer jumped all the way up to 85 (thats as high as it goes :frown:). But what is confusing me about it is that it only does it when its really cold out (here in florida thats anything under 50) so I went to pull over to see what was going on my brakes locked up and I spun all the way around and ended up in the ditch on the other side. The good thing was that my Dad wasnt to far behind me and he pulled me out with his truck. But I have to say that slide was fun. lol. So does anyone have any ideas of what could be wrong with it?

Sounds like a stripped speedo gear to me.

Sounds like a stripped speedo gear to me.
yeah but only does it when its really cold out.