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Old 06-13-2021, 06:14 PM   #1
504
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Default Intermittent speedometer & odometer

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My speedometer cuts out randomly and when it does the odometer also stops working. I thought it might be the gear initially but the gears are fine (replaced the gear previously).

A good whack on the dash will often restore functionality, but typically only for a little while. Sometimes it will only work for a few seconds before cutting out again.

I have reflowed the solder joints on the odometer motor wires, the three pin internal connector, and the three pc board tabs for the external connector multiple times. I took a file to the pins on the external connector. I have sanded the tab for the single wire connector. I have sprayed everything with DeOxit multiple times. This typically gets it working again but it doesn't last and the intermittent behavior begins again.

I have tightened up the three pin internal connector multiple times as that was my top suspect. No change. Today I tried soldering some wires to provide an additional parallel connection for the internal three pin connector, but this didn't make any difference.

I have looked around for any cold solder joints, cracked solder joints, or anything else suspect but haven't found anything yet. I saw this topic discussed in some other threads and it definitely seems to be an electrical issue.

What are some other areas that to check for flaky electrical connections that might be causing the problem? Maybe just reflow all solder joints on the board?
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Old 06-13-2021, 06:58 PM   #2
Khrrck
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Have you checked the wiring at the sensor on the differential? After 35 years of driving around and flexing they tend to wear through.
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Old 06-13-2021, 07:11 PM   #3
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Due to the fact that whacking the dash often gets it working, I don't think that is the issue. I may check that at some point. For the moment, I reflowed all the solder joints. Speedometer working, at least for now, but the odometer has stopped. The odometer stopped right after I reset the trip odometer. (Car was not moving at the time.)
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Old 06-17-2021, 01:27 PM   #4
volvowagoon
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I had this problem on my first '89 wagon. If I wacked the dash at speed the speedo and odo would come to life. I didn't look at all the solder joints because I wasn't as smart in those days, but I do remember finding an open on the speedometer where I was supposed to see the resistance value of the speedo winding. I bought a junk parts cluster with the same part number for $20 and swapped just the speedo. Problem solved, but I got lucky in finding the right part so quick and so cheap.

Maybe try checking the winding itself? You should be able to measure where the L connector goes but that would include a potential open at a solder joint too IIRC.
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Old 06-29-2021, 11:22 PM   #5
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Update. After reflowing all the solder joints, the speedometer has been working without crapping out for over two weeks.

However the odometer is still dead.

I opened it up and found that the 15 tooth gear had disintegrated. Ok, great. I ordered a new 15 tooth gear from FCP. (I had previously replaced the 25 tooth gear and it was fine.)

I replaced the 15 tooth gear and it worked for 1 mile then stopped.

I opened it up and found that the main odometer number gear and the trip odometer number gear seemed to be stuck. Perhaps there were some fragments of the 15 tooth gear somewhere in there. I blew it out with compressed air and the main number gear seems to move ok. But the trip odometer gear is a bit suspect. If I reset it, it sometimes works and sometimes is completely stuck. I am suspecting there is some alignment issue between the individual number gears of the trip odometer, but haven't figured out how to align them correctly yet.

The bigger problem is that while I can get both mileage gears to turn, when I assemble the gears with the motor board, they somehow jam up.

After putting the motor board in place, I try to turn the 15 tooth gear. You can just barely get to it with a skinny screw driver. But after installing the motor board, it won't turn. If I remove the motor board, everything turns, but after installing it, it's jammed.

What is causing the jam?

Maybe the replacement 15 tooth gear is taller than the original? (That appears to the case when viewing them side by side.)

Any other insights?
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Old 06-30-2021, 07:20 AM   #6
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You're trying to spin the trip with a screwdriver while the gears are still in place? How well does it spin with the gears removed? If spins fine in that scenario then I would blame the gear. Tolerance stacking is starting to cause issues with the reproduction gears, so a new one that doesn't work right is not out of line. I would recommend buying both gears as a set and from a good source. If the trip is still stuck with the gears removed, then you need to fish out some more debris.
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