For your info, Our odometer recently quit working on our 1997 Chinook, the speedometer still worked. After researching it I found it was a common problem and a do it yourself repair could be done. I ordered a $15 nylon gear and replaced the broken one and it's back working again. It took about 2 hours to do it. The link below gives you a general idea of what needs to be done.
http://www.f150nation.com/how-to-s/1220 ... -gear.html