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Old 02-21-2019, 08:39 AM   #1
JOHN CT
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Default Speedo gear

My Speedo is off by 5 mph on the plus side. Iíve been checking into the drive gear. I didnít rebuild the rear end. I see in the parts catalog that thereís 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?
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Old 02-21-2019, 11:34 AM   #2
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Default Re: Speedo gear

At what speed is it off by 5?
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Old 02-21-2019, 11:58 AM   #3
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Default Re: Speedo gear

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At what speed is it off by 5?
When I get 30 mph and above
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Old 02-21-2019, 12:41 PM   #4
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Default 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.
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Old 02-21-2019, 12:49 PM   #5
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Default Re: Speedo gear

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

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Old 02-21-2019, 01:13 PM   #6
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Default Re: Speedo gear

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Originally Posted by Charlie Stephens View Post
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 ?
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Old 02-21-2019, 01:15 PM   #7
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Default Re: Speedo gear

gps?
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Old 02-21-2019, 01:27 PM   #8
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Default Re: Speedo gear

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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!

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Old 02-21-2019, 01:28 PM   #9
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Default Re: Speedo gear

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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.

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Old 02-21-2019, 01:52 PM   #10
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Default Re: Speedo gear

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gps?
Iíve checked it with my gps. When Iím 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
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Old 02-21-2019, 02:49 PM   #11
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Default Re: Speedo gear

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Iíve checked it with my gps. When Iím 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)?

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Old 02-21-2019, 03:50 PM   #12
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Default Re: Speedo gear

The attached may be of help.


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Attached Files
File Type: pdf 11-Speedo housing gears.pdf (6.9 KB, 44 views)
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Old 02-21-2019, 04:23 PM   #13
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Default Re: Speedo gear

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Originally Posted by JOHN CT View Post
Iíve checked it with my gps. When Iím 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, youíll never get a speeding ticket. Besides, it wonít cost you anything.

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Old 02-21-2019, 05:29 PM   #14
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Default 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.
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Old 02-21-2019, 06:32 PM   #15
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Default Re: Speedo gear

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Originally Posted by Charlie Stephens View Post
Did you check the odometer (the part that measures mileage)?

Charlie Stephens
Good idea. I didnít think of that. If the mileage isnít accurate that would mean the hole Speedo needs repair
Thanks
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Old 02-21-2019, 06:42 PM   #16
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Default 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.
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Old 02-21-2019, 11:34 PM   #17
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Default Re: Speedo gear

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Originally Posted by JOHN CT View Post
Good idea. I didnít think of that. If the mileage isnít 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.

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Old 02-22-2019, 12:32 AM   #18
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Default Re: Speedo gear

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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
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Old 02-22-2019, 05:53 AM   #19
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Default Re: Speedo gear

>>When Iím 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
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Old 02-22-2019, 02:43 PM   #20
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Default 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: info@clarkbrothers.net
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