The Ford Barn

JOHN CT · 02-21-2019, 08:39 AM

My Speedo is off by 5 mph on the plus side. I’ve been checking into the drive gear. I didn’t rebuild the rear end. I see in the parts catalog that there’s 2 different gears that can be used in a stock rear. 18 and a 19 tooth gear. On the drive housing it has a 19 stamped on it does that mean I have to 19 tooth gear or is the housing interchangeable except ether gears?

katy · 02-21-2019, 11:34 AM

At what speed is it off by 5?

JOHN CT · 02-21-2019, 11:58 AM

Quote:

Originally Posted by katy

At what speed is it off by 5?

When I get 30 mph and above

barnstuf · 02-21-2019, 12:41 PM

The 19 stamped on your speedometer gear case means it had a 19 tooth gear when the car was made. As the gear can be changed it is easy to remove the gear and case assembly and count the gear teeth in it now. If a different gear is needed they can be changed.

Charlie Stephens · 02-21-2019, 12:49 PM

Check your odometer first. If it is correct then you have a problem with the speedometer that needs to be fixed.

Charlie Stephens

JOHN CT · 02-21-2019, 01:13 PM

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Quote:

Originally Posted by Charlie Stephens

Check your odometer first. If it is correct then you have a problem with the speedometer that needs to be fixed.

Charlie Stephens

How do I go about checking the Speedo for accuracy ?

johnbuckley · 02-21-2019, 01:15 PM

gps?

California Travieso · 02-21-2019, 01:27 PM

Quote:

Originally Posted by JOHN CT

How do I go about checking the Speedo for accuracy ?

What John Buckley said. I rely more on my GPS than the speedometer. I don't think any of the instruments on the Model A are very accurate anyway and I don't rely on them. I don't drive much over 50 and I'm too busy with the controls to notice.

There was a guy here on the Barn that used a stick to check the gas. He calibrated the stick by adding a gallon of gas to the tank until he got to 10 gallons!

David Serrano

Charlie Stephens · 02-21-2019, 01:28 PM

Quote:

Originally Posted by JOHN CT

How do I go about checking the Speedo for accuracy ?

GPS sounds good. The auto club (AAA) in southern California used to have a mobile test setup that traveled from one location to another. Your local police department might have a source.

Charlie Stephens

JOHN CT · 02-21-2019, 01:52 PM

Quote:

Originally Posted by johnbuckley

gps?

I’ve checked it with my gps. When I’m going 40 mph on the Speedo the gps shows 35 mph

so how do I fix it to be more accurate? Or should I just leave it alone

Charlie Stephens · 02-21-2019, 02:49 PM

Quote:

Originally Posted by JOHN CT

I’ve checked it with my gps. When I’m going 40 mph on the Speedo the gps shows 35 mph

so how do I fix it to be more accurate? Or should I just leave it alone

Did you check the odometer (the part that measures mileage)?

Charlie Stephens

Tom Endy · 02-21-2019, 03:50 PM

The attached may be of help.

Tom Endy

California Travieso · 02-21-2019, 04:23 PM

Quote:

Originally Posted by JOHN CT

I’ve checked it with my gps. When I’m going 40 mph on the Speedo the gps shows 35 mph

so how do I fix it to be more accurate? Or should I just leave it alone

John,

Leave it alone, you’ll never get a speeding ticket. Besides, it won’t cost you anything.

David Serrano

Synchro909 · 02-21-2019, 05:29 PM

Here, if you go more than 3 kph (2 mph) over the limit, you stand to get a ticket so we are more fussy about speedo accuracy. There was a thread here a while ago about this subject and it became clear that there is an adjustment that can be made inside the instrument to make them more accurate.
The speedo in my '30 CCPU reads 10 mph fast at 50 mph - so far off that that internal adjustment won't do it. I won't get fined for being under the limit so i have decided to leave it alone and "drive by ear".
I agree with what has been said above about check the accuracy of the odometer first, then worry about the speedo only after that is right.

JOHN CT · 02-21-2019, 06:32 PM

Quote:

Originally Posted by Charlie Stephens

Did you check the odometer (the part that measures mileage)?

Charlie Stephens

Good idea. I didn’t think of that. If the mileage isn’t accurate that would mean the hole Speedo needs repair
Thanks

AL in NY · 02-21-2019, 06:42 PM

The first thing you should do is check and see if the odometer is reading correctly. Drive somewhere where there are mileage markers along the side of the road. Check your odometer against the mileage markers. You should do it for at least 5 miles. If the reading is off, then the gear needs to be changed. If the odometer reading agrees with the mileage markers, then the problem is in the speed calibration of the speedometer. When you get to that point, let us know.

Charlie Stephens · 02-21-2019, 11:34 PM

Quote:

Originally Posted by JOHN CT

Good idea. I didn’t think of that. If the mileage isn’t accurate that would mean the hole Speedo needs repair
Thanks

I was thinking more along the lines of if the mileage and speedometer are both off by the same amount then it may be time to change the gear.

Charlie Stephens

JOHN CT · 02-22-2019, 12:32 AM

Quote:

Originally Posted by Charlie Stephens

I was thinking more along the lines of if the mileage and speedometer are both off by the same amount then it may be time to change the gear.

Charlie Stephens

Okay I understand thanks

updraught · 02-22-2019, 05:53 AM

>>When I’m going 40 mph on the Speedo the gps shows 35 mph

so how do I fix it to be more accurate?

Use 4 inch bigger tyres.

http://www.onlineconversion.com/bigger_tires.htm

bettlesr · 02-22-2019, 02:43 PM

I bought an adapter from Clark Brothers Instruments. You screw it to the transmission and then screw the cable into it. I sent them the speedometer reading and my GPS speed reading and they calculated the right ratio for the adapter. Reads dead on with my gps now.
http://clarkbrothers.net/ratio_adapters.html

56680 Mound Rd, Shelby Township, MI 48316 USA
Tel: 586-781-7000, Fax:586-781-7005, Email: [email protected]

02-21-2019, 08:39 AM	#1
JOHN CT Senior Member Join Date: May 2010 Location: In my garage Posts: 465	Speedo gear My Speedo is off by 5 mph on the plus side. I’ve been checking into the drive gear. I didn’t rebuild the rear end. I see in the parts catalog that there’s 2 different gears that can be used in a stock rear. 18 and a 19 tooth gear. On the drive housing it has a 19 stamped on it does that mean I have to 19 tooth gear or is the housing interchangeable except ether gears? __________________ 31 Tudor 66 Bonneville 57 Chevy pickup 27 T roadster pick up

02-21-2019, 11:34 AM	#2
katy Senior Member Join Date: Jun 2015 Location: Red Deer, Alberta Posts: 5,042	Re: Speedo gear At what speed is it off by 5? __________________ If you don't hear a rumor by 10 AM, start one!. Got my education out behind the barn!

02-21-2019, 12:41 PM	#4
barnstuf Senior Member Join Date: May 2010 Location: Cape Cod MA Posts: 2,840	Re: Speedo gear The 19 stamped on your speedometer gear case means it had a 19 tooth gear when the car was made. As the gear can be changed it is easy to remove the gear and case assembly and count the gear teeth in it now. If a different gear is needed they can be changed.

02-21-2019, 12:49 PM	#5
Charlie Stephens Senior Member Join Date: May 2010 Location: Southern California Posts: 7,030	Re: Speedo gear Check your odometer first. If it is correct then you have a problem with the speedometer that needs to be fixed. Charlie Stephens

02-21-2019, 01:15 PM	#7
johnbuckley Senior Member Join Date: Jul 2010 Location: United Kingdom Posts: 1,441	Re: Speedo gear gps?

02-21-2019, 05:29 PM	#14
Synchro909 Senior Member Join Date: Jun 2014 Location: Melbourne, Australia Posts: 7,496	Re: Speedo gear Here, if you go more than 3 kph (2 mph) over the limit, you stand to get a ticket so we are more fussy about speedo accuracy. There was a thread here a while ago about this subject and it became clear that there is an adjustment that can be made inside the instrument to make them more accurate. The speedo in my '30 CCPU reads 10 mph fast at 50 mph - so far off that that internal adjustment won't do it. I won't get fined for being under the limit so i have decided to leave it alone and "drive by ear". I agree with what has been said above about check the accuracy of the odometer first, then worry about the speedo only after that is right. __________________ I'm part of the only ever generation with an analogue childhood and a digital adulthood.

02-21-2019, 06:42 PM	#16
AL in NY Senior Member Join Date: May 2010 Location: Southern Upstate New York Posts: 1,160	Re: Speedo gear The first thing you should do is check and see if the odometer is reading correctly. Drive somewhere where there are mileage markers along the side of the road. Check your odometer against the mileage markers. You should do it for at least 5 miles. If the reading is off, then the gear needs to be changed. If the odometer reading agrees with the mileage markers, then the problem is in the speed calibration of the speedometer. When you get to that point, let us know. __________________ AL in NY

02-22-2019, 05:53 AM	#19
updraught Senior Member Join Date: Feb 2015 Location: Australia Posts: 1,969	Re: Speedo gear >>When I’m going 40 mph on the Speedo the gps shows 35 mph so how do I fix it to be more accurate? Use 4 inch bigger tyres. http://www.onlineconversion.com/bigger_tires.htm

02-22-2019, 02:43 PM	#20
bettlesr Senior Member Join Date: Nov 2010 Location: Florham Park, NJ Posts: 396	Re: Speedo gear I bought an adapter from Clark Brothers Instruments. You screw it to the transmission and then screw the cable into it. I sent them the speedometer reading and my GPS speed reading and they calculated the right ratio for the adapter. Reads dead on with my gps now. http://clarkbrothers.net/ratio_adapters.html 56680 Mound Rd, Shelby Township, MI 48316 USA Tel: 586-781-7000, Fax:586-781-7005, Email: [email protected] __________________ 1965 Lotus Elan S2 1930 Model A Sport Coupe