Q:

On my 1997 volvo 850 odometer stopped registering the mileage but the speedometer still works please let me know which part do I need and if I can even fix it?

A:

It is very common issue on the 850 series volvos, the odometer stops working because of on broken tooth on the 15 tooth gear inside the speedometer, Yes it  can be repaired and the tooth can be purchased from me or anybody who sells it, there is a step by step instruction how to do it

http://www.matthewsvolvosite.com/2005/01/01/interior-seats-dash-remotes-switches-odometer-fix-how-to/

Patrick