Dear Rick,

Hope you're well. Fixing a mechanically-damaged speedometer - i.e., one with a broken part (as distinct from a failed electronic component, e.g., a capacitor) - likely should be left to instrument specialists. A speedometer is a bit like watch: while a watch battery change is relatively easy, most would go to a watch-maker to deal with a mechanical failure.

Gerrit1973 recently posted that he had built a device to help assess speedometer failures due to electronic components. Getting at some of the components will require dismantling the device.

I'd guess that these Yazaki speedometers were not designed to be repaired. Rather, they were made to be replaced. I also presume the designers wanted to make speedometers hard to dismantle, to deter fraud.

When these speedometers were made - in the early-to-mid 1990s - on-line data about cars' history were not available. Preventing speedometer "roll-backs" mattered far more than now it does. On-line databases make a "roll-back" pretty obvious.

Newer, all-electronic speedometers have few, if any, moving parts. These newer instruments, surely chip-based, are also not made to be repaired. As with most electronic items, if it fails, we simply replace it entirely, or - at most - we replace the failed circuit board.

In short, I'd recommend finding a 1991-92 speedometer in good working order and replacing the capacitors preventively. I'd send the speedo to an instrument specialist to re-set the mileage to that on your car. Such a specialist will check the speedometer's calibration. At that point, you have a sound unit.

A few years ago, the speedo on my '93 940 failed. I sourced a salvage yard unit and sent it to APT Instruments (www.gaugeguys.com; APT Instruments International, Inc.; 9632 Humboldt Ave South; Bloomington, MN 55431; Tel: 952-881-709). For about $75, they re-set the mileage according to documentation I provided, checked the calibration, and returned it. It has worked perfectly.

Hope this helps.

Yours faithfully,

Spook