Technical Electronic Speedometer Discrepancy?

To all that are running an electronic speedometer.
Question 1, Have you noticed a discrepancy from what your speed reading as compared to what the odometer actually reads?
Question 2, Are you using a sender at trans or a GPS receiver for a signal to your speedometer?
Reasons for asking. I cheated by using a GPS receiver with a fixed reading of 8,000 ppm or 16,000 ppm per how it's wired. The speedo in question in a SW Wings and wired for 8,000 ppm. Instruction for speedo does not state anything about how to wire a GPS receiver however SW tech on the phone tells me I can but I'll need to re-calibrate. So I calibrated (with my o.t. 2013 GMC truck as test mule) but to get speed to read correctly I could not drive a complete mile. The magic ticket was to drive only 8/10th's of a mile. But guess what!? For every mile the SW speedo clicked off the mule only traveled 8/10th's of a mile. Not a shocker math wise but this tells me that the odometer is possibly working off a direct circuit from incoming signal.
The floor is open to any thoughts.

 

I think your speedo is defective.

Over the last 15 or so years, have installed VDO electronic speedometers in several old trucks (4 IH and 2 Ford). I have used a VDO speedo sender, a stock Ford speed sender and magnets on the driveshaft (Rostra cruise control speed sender). Calibration of these speedos uses the same drive 1 (one) mile procedure that you are using. I never found a discrepancy between MPH and miles driven. My latest Ford truck was compared to the GPS speedo on my cell phone, usually within 1 MPH at 75 MPH.

I also have a JEGS/Intelletronix digital dash in my 1966 that used a GPS receiver. It appears to be a low end/low budget/get-out-the-door design. The speedometer is worthless below 20 MPH (makes school zones "interesting" - I marked 15 MPH on my tach (not a JEGS product). At higher speeds, I get a good correlation with my cell phone GPS speedo. I converted it to drive shaft magnets, it uses the same 1 (one) mile calibration procedure - Higher speeds compare with the cell phone GPS, still worthless in school zones.

 

When I complained to the rep for Stewart Warner about the third electronic speedometer and the odometer, at this last SEMA show, he finally admitted they had a large run of speedometers with faulty odometers. He promised to get back to me after the show. But, this is May and that was November. He doesn't return my phone calls either. Classic Instruments has since told me that they call build a unit with the same font and use my initials instead of SW and guarantee it for 7 years. Stewart Warner ain't the same as it used to be, even remotely.

 

The newer Stewart Warner speedometers and gauges are made in Mexico and are junk, and there is no tech support, had 3 of the wings speedometers break for different reasons in a year and where replaced by Summit. After third broke called the good people at Summit and returned the SW gauge package for full credit and purchased a classic instrument package.
If you want to keep using the SW speedo I recommend you install it with Velcro, makes easier to keep replacing them.

 

Thanks guys. I agree that there is something wrong with it. I regretfully did look into reviews last night (a little to late now) and the HAMB had nothing good to say about SW. I will go on record and say this. It isn't Mexico, it's Steward Warner's issue. If a company is saving a butt load of money or should I say making better profit's else where. Then there is funds for top notch quality control.
I'm glad I only opened just the one gauge and tested as I did since the project isn't ready for it. For now, looks like everything is going back. Speedo, Tach, Fuel, Volt, Temp, Oil and GPS Receiver all purchased separately so I could have all the types and values I wanted over just buying a kit.

 

I have an omega run off a speedway gps sensor. Neither is top of the line, but it did calibrate pretty good. My sensor says NOT to use it under a metal dash, I do and it works fine 90% of the time. the other 10 % I just go with traffic

 

I think I read on SW web site their accuracy rating is + or - 20%

 

As a whole is one thing. But odometer reading 20% over MPH reading?

 

To close. All 7 pieces are on the way back for a refund.
I'm possibly going to do my signature move to another set of AutoMeter Tradition Chrome.

These gauges have never let me down. I had Redline Gauge Works in Newhall Ca. do some magic to them!

 

Then again? AutoMeter is having a mail in rebate good until July 31 2019. These should be fine in her 32'.