Instrument Pod

Odometer Gear Tutorial

Odometer Gear Tutorial

The odometer is powered by a small motor with a worm gear attached to it's shaft. The worm gear turns a pair of gears that are pressed together by spring tension. The smaller of the two gears has cone shaped end which fits into a dished out center on the larger gear. There are small teeth that make the two gears turn together as one unit. The problem with this arrangement is that the small teeth get worn off allowing the larger gear to turn without turning the smaller gear. Once you get past the first two gears there is another double gear that reduces the speed of the movement. It's a one piece affair so there aren't any ultra small teeth to wear out...After that one you reach the gear that moves the 1/10th mile movements in the tripmeter and the odometer. It's actually two gears with a common shaft. Here again, there's nothing to slip because they are part of the same casting....BTW, the 1/10th mile digit isn't included in the odometer like it is in the trip meter. The wheel is there but it is outside the view area so the first digit you see it the one mile digit. The trip meter is zeroed by a solenoid that pulls on a reset mechanism. It releases the digit locks and allows them to be forced back to zero. I just had a theory about what makes these units fail but while I was writing this I discovered it to be false. I thought that the reset mechanism might lock-up the gear train and force the input gears to slip. Well, it doesn't. So, they simply wear out from normal use and there doesn't seem to be anything you can do about it...I don't know what company made these units but the quality of that gear pair is really LOW! The rest of the gears are nice pieces of plastic but those two that fit together to run the whole thing are real junk!!!

Rgds,
Bob East
86.5 928S Automatic
87 928 S-4 5-speed

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Replacement gears available, below

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