Speedometer

[RedD250]

Hey all,

The speedometer in my '93 D250 is inaccurate by anywhere from 5-12 MPH, depending on how fast I am going. At very low speeds, like 20 or less, it seems to be accurate. Sometimes 40 indicated on the gauge is actually 49, sometimes it might be 50, 51, 52... not consistently off, but always off. The needle does not bounce around, it's got smooth action, so I don't think the cable needs greased. And the liklihood of the speedo gear having been changed is pretty much nil... this was a grandpa truck, and is still on stock size tires. Absolutely zero modifications to it. The odometer shows slightly more miles than actually traveled (around 3 over a 50 mile drive), which means that my 194,000 mile truck probably has several thousand less miles than indicated, depending on how long this has been going on

My logic says that since the speedo does work smoothly, just inaccurately, that none of the little gears are broken, either. Could this be the VSS? If so, where exactly is the VSS located on these trucks?
Thanks!

 

[AnonEd]

The sensor should be driver's side toward the rear of either gearbox according to the book. It mentions a sensor test in a "Vehicle Diagnostics Test Procedure Manual" which you may be able to find online. My speedo was quite optimistic from the factory...slightly larger tires brought it closer.

 

[RWherley]

AnonEd is correct, the VSS is at the left rear of the tail shaft of the transmission, I've had the same issue on mine the issue is the square drive socket inside the drive pinion rounds out and doesn't transfer the true speed to the VSS

 

[RedD250]

Good to know. Hopefully that part is still available if it's worn. Thank you!