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Old 10-11-2017, 07:53 AM   #1
Steve Rinaldo
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Default speedometer drive gear

I have a 1930 "A" and the speedometer reads 5 MPH slow. Which drive gear should I use to try and correct this. I have 19 in. wheels
Thanks, Steve
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Old 10-11-2017, 09:33 AM   #2
SSsssteamer
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Default Re: speedometer drive gear

Looking for the percentage of error to find the percentage of speedo gear change. Is it 5 mph slow at 10 mph, or 5 mph slow at 50 mph?
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Old 10-11-2017, 09:39 AM   #3
Mark in MT
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Default Re: speedometer drive gear

Check the odometer with mile posts on the highway to see if it is off. If it is off in the same direction by the same percentage as the speedometer, then change the drive gear. The change of one tooth will make a difference of about 1/19 or 6%.

If the odometer reads correct the error is in the calibration of the speedometer, which is adjustable.

If you take it out, try to turn the input with your finger tips to see how easily it turns. If it is stiff, it should be serviced, they all need service every 85 years or so.
www.marksspeedometer.com
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Old 10-11-2017, 11:39 AM   #4
duke36
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Default Re: speedometer drive gear

We tried changing the speedo gear with a different tooth count from the vendors (9-34 housing) also based on non stock tranny issues and it didn't work and mesh properly. Went back to the stock gear and a Speedo Gear Adapter based on ratio, or % high or low with some math calcs.. Not cheap, but can be found on ebay and can be provided with varying cable end adapters. Checked with cell phone app. and speed is accurate.
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Old 10-11-2017, 05:20 PM   #5
Steve Rinaldo
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Default Re: speedometer drive gear

Thanks. I think I'll live with it.
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Old 10-11-2017, 05:29 PM   #6
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Default Re: speedometer drive gear

When you are driving 50 MPH, does your speedo read 45 or 55?.
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Old 10-12-2017, 10:25 AM   #7
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Default Re: speedometer drive gear

Mark (post #3) does excellent work and reasonably priced.
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