Contrary to contemporary Germanic myth, even BMW speedometers screw up. GASP! I know that's difficult to believe, but what you see here--on the left in the instrument module--is a dead one. At least, the odometer is dead.
So let's see vas ist kapoot. This is the back of the module. Simple, eh? [That row of lights across the bottom is a sequential warning system tied to increasing speed, to tell a Bimmer pilot how close he/she is to going to jail].
Well yes, simple so far. Remove 8 screws and lift off the plastic outer housing. We're not there yet....
Take out some more screws and whaddaya know? A speedometer! And that little gauge at the base of the tachometer? It is fuel mileage gauge, but in litres per 100 kilometers. See, Bimmer drivers have to have SOMEthing to wow the drivers of LESSOR cars that happen to ride with them [and they explain how it works while speaking German, of course].
This speedometer was built when--apparently--neither BMW or VDO had figured out if they wanted to fish or cut bait. Mechanical operation or electrical? GOSH! I don't know---let's do BOTH. So they did. The speedometer is electric, much like a tachometer. The odometer is driven by a wee electric motor, through a fairly complex gear train.Obviously, they did it because the COULD, not necessarily because it made good sense. So what screws up? Those gears are plastic [of course] and one or more of them get tired of it all and spit off a tooth or two. In this case, TWO gears spit teeth. You can see the dark brown gear [bottom center] that's missing a couple of teeth. Harder to see is a WEE LITTLE shit of a gear just at the bottom of the other brown gear, still in the speedometer apparatus. It's minus a couple of teeth too. The more or less clear plastic housing to the left of the speedo body supports the gear train shafts and keeps the gears in place.
The three new gears are at the lower left. The only fly in the ointment is removing the chewed up WEE gear [that is still on the shaft in this photo]. That shaft is pressed into the wee electric odo drive motor. If you reef on the wee gear to get it off, you'll pull the guts out of the drive motor and that will turn your whole day very dark brown. I used one of my special pullers to remove the little shit. The two new larger gears just drop onto their respective shafts [in the correct order and location--they do not have the same number of teeth]. The new WEE gear has to be carefully pressed onto the motor drive shaft--to the correct depth. Oh yeah, it's great fun repairing something that was a crap design in the first place.
But, here it is--ready to rip once again, and log many happy miles at speeds well above any posted speed limit. Anywhere.
City Car Design
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