trip-meter and odometer have stopped working

I have a 96 Ford Explorer V8. A couple months back ago my trip-meter and odometer would stop working occasionly. In the past 2 weeks they have completely stopped working.

I am not that auto savay but am willing to try and fix the problem myself, or at least determine what the problem is, before spending the money to have a mechanic look at it.

I have read where it's possible that dirt or something is caught in the gears causing it to stop working and blowing air up in there might release the dirt. Not that I think this is the problem but maybe it is with investigating.

Is there an easy way of getting to the working parts of the tripmeter and odometer?

Are there any suggestions that could get me started?

Thanks in advance for your help.