If you replace the speedo you should keep the old one, but better is to also program the new one with the old mileage.
A speedo shop could not do it, as it is made difficult so as to prevent people from tampering with them. You can send it to VDO and they will program it, but a few years ago they were charging $120. I thought this was silly.
So I bought a sender at a speedo shop for about $15. Hooked it to a small electric motor, connected a small 12 volt battery, programmed the speedo to think it was going 85 mph at the speed the motor turned the sender. Set it up on the workbench. Then just let it run!
100,000 miles takes about 8 weeks, but hey, I had time. The bus sits for weeks at a time anyway.You just need to be sure you turn it off at the right moment.
After that you reprogram the speedo to the correct setting for the coach based on axle ratio and tire size. You can adjust that to be exact.
A fun project, does not cost much, is clean, and satisfying. I bought my replacement speedo on eBay for about $70, brand new. There was a complet description and pics on the POG site a few years back.
Peter van Schoonhoven
1994 Marathon XLV
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