Speedometer creeping up but speed remains steady??

[studmuffin]

We just got a 2001 Dynasty, 40 foot, tag axle, with a 370 Cummins. Driving home had a strange problem. At a steady speed, 60 MPH, checked against the inner state mile markers, on cruise control, the sppedometer started creeping up. At first I thought the cruise was bad, but after checking mile markers and tach readings, found no actual speed increase. Went from indicated 60 MPH, at the start of the trip, up to indicated 75-80 MPH after about 10 minutes. The speedo then stayed steady at 80ish. When I slowed down the speedo slowed down but still reading high at slower speeds. The cruise stayed working and we were going 60 and that never changed. I think the speedo sensor is OK, because the cruise was steady, so under the dash or the speedometer, it self, might be bad?? Any ideas would be appreciated, as I can see the need for a working speedo, but a dealer repair would take about $10000, cause of the trouble shooting involved. Help the zipping along Muffin Man.

[studmuffin]

We just got a 2001 Dynasty, 40 foot, tag axle, with a 370 Cummins. Driving home had a strange problem. At a steady speed, 60 MPH, checked against the inner state mile markers, on cruise control, the sppedometer started creeping up. At first I thought the cruise was bad, but after checking mile markers and tach readings, found no actual speed increase. Went from indicated 60 MPH, at the start of the trip, up to indicated 75-80 MPH after about 10 minutes. The speedo then stayed steady at 80ish. When I slowed down the speedo slowed down but still reading high at slower speeds. The cruise stayed working and we were going 60 and that never changed. I think the speedo sensor is OK, because the cruise was steady, so under the dash or the speedometer, it self, might be bad?? Any ideas would be appreciated, as I can see the need for a working speedo, but a dealer repair would take about $10000, cause of the trouble shooting involved. Help the zipping along Muffin Man.

[20 gauge]

Buy a GPS and save yourself 9.5k

[AKBrick]

20 gauge makes a good point. The Garmin 7200 that I have has an MPH readout that is very easy to read and is very accurate. It matches my speedo. The only bad thing about it is that my wife can read it too when she's the passenger!!
AKBrick

[Alfa38User]

You may find the sensor for the speedo and the sensor for the Cruise Control are two different units. Check with the chassis manufacturer first.

The GPS idea is good just the same though!!!!!