A while back someone posted a thread about a speedometer app on his phone. My son helped me find it and download it to my phone.

I knew the speedometers on my truck were not accurate with my 54 being way off.

Here's what I found. My 55 speedo is 3 to 5 mph fast. The faster I go the more it is off. So if my speedo says 60 I'm really doing 55mph and thats maxing out for my F350 with a 5.83 rear end.

The speedo in my 54 is 5 to 9 mph too fast. Like 5 mph off at 30mph and 9 mph off at 70. So if my speedo says 70 I'm actually doing 61mph. And that's about as fast as I go.

I was going to take a picture for you guys but suddenly realized I can't take a picture with my phone when it's lying on the dash!

 

I have observed the same non-linear behavior on my '52's speedo. 10% low up to about 50 (which is to be expected with the 3.50 gears that are 10% lower), then it increases to 15% at 65.

Are you using Ulysse app?

 

Yes, when speedo is off its a non linear error.
I use a speedo app now and again, typically for a few miles out on a road trip, the rest of the time I just wing it.
My speedo is off about 4MPH at 70MPH.

Bobby

 

No, it is called Cool Niks, I think.

 

Why would my 54 speedo be so off? I haven't changed the rear end. I have stock size tires (6.00) on 16 inch wheels. I ​​​​​​think i replaced the speedo head back in 1999. I know I replaced the odometer but am not sure if I cleaned up the speedo and put it back in the instrument panel or if I cleaned up one from a junk yard. But that shouldn't matter, right?

 

My speedometer seemed fairly accurate, but it bounces a bit, so getting exact is not easy. I need to lube the cable.
I have an app for my iphone named Speed Box. I could't find the two you guys mentioned.
I think I downloaded a couple of different ones. They are handy for double checking your speedometer. I used it in my daily driver to see how accurate the app was. (assuming my dd speedometer is accurate)

 

I use Speed Box, downloaded from the Apple app store. Excellent free app. A company that advertises in Street Scene sells a small gear box which connects to the speedo cable and the trans which corrects any error.

Regards, Mark.

 

A 5:83 rear? What are you doing, drag racing?

Later!
Mr. Ed

 

My 54 which is all original also reads about 10% higher than actual speed.

 

Do you have a name for that company? The places I've seen those sell a unit for like $150, apparently milled out of gold bars.

 

 

 

These old mechanical speedometers were notorious for being inaccurate. In days of old, the auto testers sometimes used a fifth wheel speedometer and reported the inaccuracies.

 

Hardley! The standard rear in a 55 F350 was a 5.18. For some reason the original owner ordered the truck or bought it off the lot with the optional 5.83 rear. They owned an orchard, to perhaps they used it to pull stumps.

 

The days are long gone when most large cities had several speedo shops. A spinning drum with magnets magically tugging at another drum (or cross bar) inside it, tensioned by a watch spring, didn't make for great accuracy in a high volume production part. Your readings fall about right in the middle of expected error/tolerance for the time. Also, don't discount the possibility of GPS 'tolerance' also. Plus, your phone isn't a dedicated GPS device, there's a lot of other things that could be sucking up CPU cycles at any time while you're GPSing and cause minor inaccuracies. If you want another source for verification try doing 45 through a a school zone once school re-opens. ;-)