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Join Date: May 2005
Location: Cridersville, OH
Posts: 1,879
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Speedo off after fixing odom. gear?
I removed my electronic speedo last week to fix the odometer gear (which happened to be a piece of dirt) and now it shows ~ 10 mph off. I've checked all connections and grounds and all seem good. Any thoughts?
I did drive it a couple of miles without the speedo installed. Could I have screwed up the sensor by doing that?
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75 911 Indian Red- RUFWAN2B 2000 Boxster 2000 & 2007 Dobies www.stahlwerks.com Cages and preparation for your Porsche “People who never make mistakes must get tired of doing nothing” Bill : The origin of the orgy of Porsche |
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07-21-2010, 05:27 PM
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Most likely the needle isn't where it needs to be in it's rotation. You might have to move it cw or ccw. You didn't close up the case yet did you?
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John Original owner '81 911SC blackmetallic coupe. Terbatrol, SSI, M+K Gen 4, SC+ cams, A/C delete, console delete, heater backdate, 7 & 8 x 16 Fuchs with polished rims, Turbo tie rods, tensioner update, Rennline engine mount bar, Mainely Custom sump plate, new top-end, corner balance. |
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07-21-2010, 05:45 PM
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Join Date: May 2004
Location: Boulder, Colorado
Posts: 7,275
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You can't hurt the sensor.
It is just a magnetic reed switch, opened and closed each time one of the 8 magnets attached to a plate by the differential passes by it. A closed switch grounds the signal wire from the instrument. This speedo converts the digital-like signal created by the grounding of the signal wire into an analog voltage. I believe the voltage drives a motor at varying speeds, and the motor drives a magnetic cup in the way the old cable speedos worked. The faster the cup revolves, the more it drags the needle against its hair spring. But there may be more to this. In any event, this same motor drives the odo gears. But otherwise I don't think there is any connection. So I don't know what went wrong. There is a variable resistor (or capacitor) which adjusts all this. Part of the D/A system, one supposes. You have to have the case off to access it unless you have drilled a strategically placed hole in the case for your small screw driver. While I doubt you disturbed this when futzing with the gears, maybe? That's my best guess on any of this. Note it is a guess. Walt |
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07-21-2010, 07:37 PM
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Join Date: May 2005
Location: Cridersville, OH
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Thanx, guys. I'll tear it back out and check that I didn't bump anything.
Is there a thread for the hole in the case for ajdustment?
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75 911 Indian Red- RUFWAN2B 2000 Boxster 2000 & 2007 Dobies www.stahlwerks.com Cages and preparation for your Porsche “People who never make mistakes must get tired of doing nothing” Bill : The origin of the orgy of Porsche |
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07-22-2010, 05:09 PM
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1981 Porsche 911SC
