There is a tiny gear inside of your odometer which tends to loose a tooth or two and stops the odometer and trip meter from working. This is a common volvo fault. The instrument cluster has to be extracted from the dash and disassembled to replace this tiny gear. Check odometergears.com for instructions on how to do this and purchase the gear.

The timing belt change interval on earlier version volvo 850s is 50,000 or 60,000 miles (check your manual). On later versions like may 96 850 it is 70000 miles. When in doubt always do the belt unless someone was nice enough to put a change sticker on the timing belt cover on the left side of the engine. Beware! The 850 B5254 engine is an interference engine. This means when your timing belt breaks, the valves an pistons occupy the same space (which they were not designed to do) and destroy each other which will require a major rebuild or a new engine.