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Speedometer repair


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I posted several months ago about my 1939 speedometer stalling at 15mph. I got some good replies and will soon be removing it from the dash to clean and lube it. One reply stated that it is likely that the magnets need to be re-magnetized. If cleaning and lube doesn't work, is there somewhere to send  the magnets to have it re-magnetized? Can I do it myself?

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8 hours ago, Dennis Detweiler said:

I posted several months ago about my 1939 speedometer stalling at 15mph. I got some good replies and will soon be removing it from the dash to clean and lube it. One reply stated that it is likely that the magnets need to be re-magnetized. If cleaning and lube doesn't work, is there somewhere to send  the magnets to have it re-magnetized? Can I do it myself?

I have some locations out here in SoCal, but that may not suit you.  If you cannot find a speedometer shop near by, please let me know.  I can send you a couple of great places that will make your speedometer good as new again.  Or at the least, repaired...

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  • 1 year later...

Maybe not the best thread to post this question in, but I got sort of tired of looking at all of them after I got to page 5 out of 53 in the search results. 

 

Here's the deal.  There is some sort of dried out goop on the main spring of the speedometer needle.  It appears to me to be dried up white lithium grease.  Most if it was down in the sort of cup, but some is on the spring itself, and the needle jerks when the two spots where it is rub past each other.  If that's what it is, can someone tell me what would dissolve it - something I could very selectively apply just to the spring?  I have acetone, brake cleaner, stuff like that.  What would you suggest using?

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My speedometer works perfectly when I first leave the driveway.

But, after I stop the first time the needle then drags way behind - I can to 50 and it shows 10.

It never goes back to being accurate unless it sits like over night.

 

 

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14 hours ago, Sniper said:

a Q tip soaked in WD40 will cleanup the grease you mention, just be patient and gentle.

 

Figured I'd use your idea, only put it on steroids.  I packed the area with cotton and then soaked it in WD-40.  (I know me.  I might have gotten too aggressive, even with the Q-Tip, and probably impatient as well.  So now it sits over the week end, or maybe I'll soak it again tomorrow.)  I kinda' don't expect that anything is going to dissolve it.  Maybe it isn't white lithium grease.  It is certainly pretty hard stuff.  If it doesn't come off w/o getting aggressive, then it will just have to stay there.

 

Another repair question: Is the whitish paint on the odometer wheels a reflective paint?  (There is a small area on one of the wheels that has a small area with the paint chipped off.) I reckon there are places that would do a complete restore job on it, but if I cannot fix it myself, it will stay as it is.  Just thought of this - if the wheels are identical, I could switch it around for the 5th digit wheel.  Then I'd only see the scratched place every 100,000 miles.  (ha ha.)

 

Speaking of the odometer, do you all set it back to zero after a major rebuild (like frame off, engine over-haul, repaint, new upholstery, etc.)?  I figure to leave mine where it's at.  That way I'll get to see it roll over sooner.  (It has over 91,000 on it now.)

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In some parts of the world, tampering with odometers is a big no-no. I wouldnt think it matters in our old rigs. 
i would leave my odometer as is,as it reflects the life it had lived. 

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I took the odometer assembly apart, and moved the scratched wheel from the hundreds spot to the ten thousands spot.  (All of the wheels are identical except the tenths, which of course is white on black, instead of black on white.)  So now the scratched '6' will not appear until the odometer rolls around to 60,000 miles.  Much chance of that?!?  (Current mileage is 91,712.2.)  I know I will never see it roll around that far.

 

I mentioned it in another thread, but has anyone added turn signal indicator lights into the speedometer back plate?  (I kinda' remember reading about someone doing that, but it didn't come up in a search.  I saw the stuff about the optional high beam indicator bezel that had the two arrow signal indicators.  Probably about is scarce as hens teeth.)

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My 1939 plymouth speedometer shaft actually broke so I sent it out to an instrument shop here for repair.  Mark of Clawson's Instruments did an awesome job explaining to me what was wrong and what he needed to do to fix. It as found that the only way to get a new shaft was to get another donor speedometer that had the same mechanisms.  These speedometers are very particular in what manufacturer was used for certain years.  1939 happens to be one that is very particular.  I found that the 1938 Dodge Motometer mechanism is practically the same as the 1939 Plymouth Motometer mechanism and he was able to use one I found cheap on ebay as a fix.  I highly recommend his services if anyone needs to have their speedometer repaired.  The price paid was also very reasonable.  I supplied my own parts so it was just labor he charged and it ended up only being a couple hours of work.  Cost me less than $200.  The '38 Dodge speedometer cost me $50 and ebay.  I actually got to go to his shop and watch him work on it, which was cool.  He also remagnatised mine as that was needed due to the inaccuracies.  

 

 https://markclawson.com/

Edited by Polsonator2
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18 minutes ago, Polsonator2 said:

My 1939 plymouth speedometer shaft actually broke so I sent it out to an instrument shop here for repair.  Mark of Clawson's Instruments did an awesome job explaining to me what was wrong and what he needed to do to fix. It as found that the only way to get a new shaft was to get another donor speedometer that had the same mechanisms.  These speedometers are very particular in what manufacturer was used for certain years.  1939 happens to be one that is very particular.  I found that the 1938 Dodge Motometer mechanism is practically the same as the 1939 Plymouth Motometer mechanism and he was able to use one I found cheap on ebay as a fix.  I highly recommend his services if anyone needs to have their speedometer repaired.  The price paid was also very reasonable.  I supplied my own parts so it was just labor he charged and it ended up only being a couple hours of work.  Cost me less than $200.  The '38 Dodge speedometer cost me $50 and ebay.  I actually got to go to his shop and watch him work on it, which was cool.  He also remagnatised mine as that was needed due to the inaccuracies.  

 

 https://markclawson.com/

Since you were there when he did the work, I'm curious if he spun it up to calibrate the speedometer to accurate speed as relative to the odometer.  (In other words, if you spun it at 60 MPH steady for exactly an hour, the odometer should also have moved exactly 60 miles.) 

When I have done on-line searches about calibrating a speedometer, if it isn't about how to mess with the modern electronic ones, then it's about getting the right gear set at the transmission to adjust for different size tires, etc.  The part I would like to know about has nothing to do with anything outside of the speedometer itself - only the tension or resistance setting of the main spring, and of course also related to the magnet issue, which you mention, and about which I knew nothing until reading here on the forum.  I hadn't though about it that the magnets might loose their magnetism.

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the magnetism only affects the needle, the odometer is directly gear driven so even if the speedo is off the odometer should be accurate, assuming nothing else int he setup (tire size, speedometer pinion gear) is correct.  In my case I put in an aftermarket gauge cluster and gauges so my odometer's reading is what it is, less than 500 miles.  As far as the State of Texas is concerned my mileage reading is exempt, which has nothing to do with my gauge swap since I got the title before that.  Not sure what makes it exempt under TX law, but it's not an issue.

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Regarding the stuff stuck to the main spring on my speedometer, as I said above, I stuffed the area with cotton, and soaked it with WD-40.  Soaked it again a day or so later.  I don't really know what it was, because it didn't really dissolve.  But having the cotton stuffed in there, I was able to use one small jeweler's screw driver to hold the spring over against the cotton, and use another one to chip enough of that stuff off that the different spots don't catch against one another anymore.  

 

Haven't put it back together yet - still looking at how I could add turn signal indicator lights into the face of the speedometer.  (I know it's no big deal, but think it would be a nice touch.)

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