The Ford Barn

Steve Rinaldo · 10-11-2017, 07:53 AM

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

SSsssteamer · 10-11-2017, 09:33 AM

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?

Mark in MT · 10-11-2017, 09:39 AM

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

duke36 · 10-11-2017, 11:39 AM

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.

Steve Rinaldo · 10-11-2017, 05:20 PM

Thanks. I think I'll live with it.

Licensed to kill · 10-11-2017, 05:29 PM

Sponsored Links (Register now to hide all advertisements)

When you are driving 50 MPH, does your speedo read 45 or 55?.

katy · 10-12-2017, 10:25 AM

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

10-11-2017, 07:53 AM	#1
Steve Rinaldo Member Join Date: May 2010 Posts: 89	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

10-11-2017, 09:33 AM	#2
SSsssteamer Senior Member Join Date: Nov 2010 Location: Sedro-Woolley, WA Posts: 1,023	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?

10-11-2017, 11:39 AM	#4
duke36 Senior Member Join Date: Jun 2015 Posts: 1,414	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.

10-11-2017, 05:20 PM	#5
Steve Rinaldo Member Join Date: May 2010 Posts: 89	Re: speedometer drive gear Thanks. I think I'll live with it.

10-11-2017, 05:29 PM	#6
Licensed to kill Senior Member Join Date: Aug 2016 Location: Alberta Posts: 930	Re: speedometer drive gear Sponsored Links (Register now to hide all advertisements) When you are driving 50 MPH, does your speedo read 45 or 55?.

10-11-2017, 09:39 AM	#3
Mark in MT Senior Member Join Date: May 2010 Location: Western MT Posts: 218	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 __________________ Mark in MT Always looking for another opportunity to be wrong.

10-12-2017, 10:25 AM	#7
katy Senior Member Join Date: Jun 2015 Location: Red Deer, Alberta Posts: 5,042	Re: speedometer drive gear Mark (post #3) does excellent work and reasonably priced. __________________ If you don't hear a rumor by 10 AM, start one!. Got my education out behind the barn!