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Speedo/Odometer testing and repair 900 1992

Hi All. I have a 1992 940T with Tazaki instrument cluster. About a year ago the speedo failed and, following the great instructions in the 700/900 FAQ pages of this site, I bought the capacitor package and replaced the capacitors on the circuit board. This fixed the speedo problem but the odometer wasn't fixed. I'm assuming there is a mechanical problem with the gears. I've read the instructions in the FAQs but it doesn't exactly explain how to remove the odometer gears or how to test them. I would really like to fix the odometer so I just bought a used cluster from a 1995 940/960. I realized that according to the FAQs the 1995 cluster is not interchangeable with 1991-1994 clusters, but it has a KPH speedo so I took a chance that maybe the odometer gear section might be the same. I don't want to interchange the two entire clusters, just swap the odometer gears and maybe the speedo circuit board. I don't have the cluster out of my '92 right now to compare them but the speedo from the '95 looks very similar, particularly the circuit board/odometer gear section. My questions are: first is it possible to test the odometer function with the speedo removed from the main circuit board? It appears there are only four electrical connections - "S-" S+" and two other screws that mount the speedo unit to the circuit board. I would like to confirm that the used speedo/odometer I just got actually works before tearing back into the cluster in my car. Is there some way to make the odometer motor run outside of the main cluster? Another question I have is - if the gears do run and the unit appears to work OK how hard is it to reset the odometer mileage to the mileage on my original odometer to closely reflect the actual mileage on my car? Has anybody successfully disassembled the odometer and got it working again? If I start to take the unit apart will the disassembly steps be easy to see or will I encounter booby traps? Thanks.








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Speedo/Odometer testing and repair 900 1992

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







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