Speedo gear

JOHN CT

JOHN CT

Senior Member
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?
 
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.
 
JOHN CT said:
How do I go about checking the Speedo for accuracy ?
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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
 
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.
 
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.
 
JOHN CT said:
Good idea. I didn’t think of that. If the mileage isn’t accurate that would mean the hole Speedo needs repair
Thanks
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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
 
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