The Ford Barn

cowtown · 09-01-2018, 06:01 PM

I have a 49 tudor that the speedometer reads faster than I am really driving. When the speedo reads 60 mph I am really going about 52-53 mph. I am running a 21 tooth gear which I thought was original to the car. (16,000 mile original car) Should I be running a 19 tooth gear???

JSeery · 09-01-2018, 10:26 PM

There are usually charts that specify rear axal gear ratios and tire size to a recommended speedometer gear (tooth count). The green book has such a list for pre-49 car/trucks. Should be a similar table for post-49.

Phil Gillespie · 09-01-2018, 10:50 PM

Quote:

Originally Posted by cowtown

I have a 49 tudor that the speedometer reads faster than I am really driving. When the speedo reads 60 mph I am really going about 52-53 mph. I am running a 21 tooth gear which I thought was original to the car. (16,000 mile original car) Should I be running a 19 tooth gear???

As mentioned the correct tyre size and rear end ratio aas per chart and if this is correct then go with the recommended tooth count as per chart.
Dropping down to a 20 tooth could assist. A 19 tooth could be too much.
Had similar problem and ended up removing speedo for calibration check.
Phil NZ

Charlie Stephens · 09-01-2018, 11:05 PM

How does the odometer read? If it is correct then it is time to fix the speedometer.

Charlie Stephens

rotorwrench · 09-02-2018, 08:14 AM

There used to be a lot more speedometer shops that had equipment to check accuracy back in the day. Now, not so much. The chassis parts book for the shoe box Fords will list the gears. I just hope you can find the one that matches your axle ratio and tire size. If you find that you already have the correct gear for your combo, your only recourse would be to get the speedometer serviced and calibrated.

38bill · 09-02-2018, 11:24 AM

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If the speedometer is reading fast then you need a larger driven gear to slow the cable down. When I was running a std driveline with a 3:54 rear end I moved from a 19 tooth gear up to a 21 tooth. The 19 read way too fast and the 21 got me about as close as you are. There are also some adjustments that can be made to the speedometer itself. I'm just crazy enough to try to fix almost anything and I was able to get mine within a couple of mph's by messing with the speedo adjustments. You may want to send yours in to an expert.

rotorwrench · 09-02-2018, 05:50 PM

Stewart Warner made ratio adapters that can be installed in line with the cable but I don't know if they fit the old drives. It would take some research to find out.

papanick · 09-03-2018, 10:39 AM

Hay I can service your speedometer and set the speed.Email me at [email protected]

I do have the equipment to calibrated the speed.

09-01-2018, 06:01 PM	#1
cowtown Senior Member Join Date: Mar 2016 Location: Montana Posts: 189	Speedometer gear question I have a 49 tudor that the speedometer reads faster than I am really driving. When the speedo reads 60 mph I am really going about 52-53 mph. I am running a 21 tooth gear which I thought was original to the car. (16,000 mile original car) Should I be running a 19 tooth gear???

09-01-2018, 10:26 PM	#2
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Speedometer gear question There are usually charts that specify rear axal gear ratios and tire size to a recommended speedometer gear (tooth count). The green book has such a list for pre-49 car/trucks. Should be a similar table for post-49.

09-01-2018, 11:05 PM	#4
Charlie Stephens Senior Member Join Date: May 2010 Location: Southern California Posts: 7,305	Re: Speedometer gear question How does the odometer read? If it is correct then it is time to fix the speedometer. Charlie Stephens

09-02-2018, 08:14 AM	#5
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 17,411	Re: Speedometer gear question There used to be a lot more speedometer shops that had equipment to check accuracy back in the day. Now, not so much. The chassis parts book for the shoe box Fords will list the gears. I just hope you can find the one that matches your axle ratio and tire size. If you find that you already have the correct gear for your combo, your only recourse would be to get the speedometer serviced and calibrated.

09-02-2018, 11:24 AM	#6
38bill Senior Member Join Date: Apr 2014 Location: Minnesota Posts: 1,200	Re: Speedometer gear question Sponsored Links (Register now to hide all advertisements) If the speedometer is reading fast then you need a larger driven gear to slow the cable down. When I was running a std driveline with a 3:54 rear end I moved from a 19 tooth gear up to a 21 tooth. The 19 read way too fast and the 21 got me about as close as you are. There are also some adjustments that can be made to the speedometer itself. I'm just crazy enough to try to fix almost anything and I was able to get mine within a couple of mph's by messing with the speedo adjustments. You may want to send yours in to an expert.

09-02-2018, 05:50 PM	#7
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 17,411	Re: Speedometer gear question Stewart Warner made ratio adapters that can be installed in line with the cable but I don't know if they fit the old drives. It would take some research to find out.

09-03-2018, 10:39 AM	#8
papanick Senior Member Join Date: Mar 2012 Location: gouverneur n,y, Posts: 2,840	Re: Speedometer gear question Hay I can service your speedometer and set the speed.Email me at [email protected] I do have the equipment to calibrated the speed. Last edited by papanick; 09-03-2018 at 05:40 PM.