Speedometer accuracy

Graham

Graham

Junior Member
Has anyone seen this before. I removed the speedometer (round Stewart Warner) to send in for rebuilding and found that if I hold it sideways, it shows the
correct speed. But when mounted properly, the speed is very innacurate (shows 10 when 35). Is there anything I can do to correct that other than mount it sideways or is it time for a rebuid? Odometer works perfectly.
Thanks
 
I had a '65 Harley Davidson M-50. The speedometer would behave just like you described. I finally checked the cable and discovered some internal fraying. I ordered a new cable and kept it oiled. The problem disappeared.

I can not say that is your problem but worth exploration. I'd like to hear the other comments for my own knowledge base.
 
Graham said:
Has anyone seen this before. I removed the speedometer (round Stewart Warner) to send in for rebuilding and found that if I hold it sideways, it shows the
correct speed. But when mounted properly, the speed is very innacurate (shows 10 when 35). Is there anything I can do to correct that other than mount it sideways or is it time for a rebuid? Odometer works perfectly.
Thanks
Click to expand...

I have one of those speedos in being re calibrated right now. Like yours, the odometer is right but the speed was about 16% high. New numbers on the speedo at the same time. I didn't bother playing with it like tilting it sideways - I intend putting it back the right way up.:D
 
Graham said:
Has anyone seen this before. I removed the speedometer (round Stewart Warner) to send in for rebuilding and found that if I hold it sideways, it shows the
correct speed. But when mounted properly, the speed is very innacurate (shows 10 when 35). Is there anything I can do to correct that other than mount it sideways or is it time for a rebuid? Odometer works perfectly.
Thanks
Click to expand...

sideways doesnt have gravity pulling down on the pivot points so it may read correct. once its right side up a worn out pivot point will cause it to bind. Best to send it to a well known re builder that also calibrates them.

it deffinately cant hurt to pull the inner cable out and clean and relube as well.
 
The speedo is calibrated by moving a tab on the roatating magnet.

This can be done by taking out of the case if you do not have the special tools.

I got clever and found the rpm to mph chart and made a quick rpm counter. I used a battery drill to turn the rpm and set the mph. I used a photo transister rpm circuit I found online and a multimeter that told me Hertz frequency.

There is a motor for a Mercedes seat motor that has short square ended flex cable that might help in making up a tester. Go to a local place and ask if they have any laying around.
 
The speedcup with the numbers on it is not balanced, and does not set level in the unit. The best way of calibrating is to use a known input speed and adjust it in its proper orientation . Adjust it by moving tab on magnet, tweeking hairspring or recharging magnet if necessary. When all else fails, send it to me.
 
If it were mine, I'd box it up and send it to Leonard Nichols, AKA PappaNick.

I know when I'm in over my head. But that's just me.
 
That's some really good advice, and it makes sense that a pivot is causing friction or the scale is out of balance. I suspect having it rebuilt is the safe way to go, as it does have 94,500 miles on it. I haven't taken the back off, and was hoping there might be a simple lube point, but it appears to be more involved than that.
If I get brave enough, I may look for the tab to recalibrate, but I'm getting a sense that it may continue slowing and a rebuild might be good measure to retain its accuracy for it's next 100k miles.

Thanks everyone for really good options.
 
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Graham said:
That's some really good advice, and it makes sense that a pivot is causing friction or the scale is out of balance. I suspect having it rebuilt is the safe way to go, as it does have 94,500 miles on it. I haven't taken the back off, and was hoping there might be a simple lube point, but it appears to be more involved than that.
If I get brave enough, I may look for the tab to recalibrate, but I'm getting a sense that it may continue slowing and a rebuild might be good measure to retain its accuracy for it's next 100k miles.

Thanks everyone for really good options.
Click to expand...
I am pleased with papanicks work. And yes I recommend sending it unopened to one of the gurus for cleaning, restoring (if you want - or leave the patina), repair, and calibration. Meantime you can pull your speedometer cable out and check for fraying and clean and relube so its all tip top shape for when the speedometer comes back.
 
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