Helping a buddy with his '96 Dump Truck. I think it is an F650 but there a no markings. It is small as dump trucks go, but has air brakes and an automatic transmission.

The speedometer goes back and forth full scale as if a speedometer cable were bad. Problem with that is, my buddy says it has an electronic speedometer. About the only thing I can think of that would cause that problem is the Vehicle Speed Sensor.

Anyone ever dealt with this one before?

Thanks in advance for your help.

 

Okay, more information.

The truck has a Cummins and Allison. I wasooking around under it yesterday but did not have on work clothes so that i could really get under it. I did not find a sensor on the rear axle. It must be on the transmission. I googled around and couldn't cind much about a VSS on an Allison.

Any suggestions?

 

OSS? Output Shaft Speed sensor?