Hey Gurus, In all my trucking years, never replaced a speed sensor so I don't know about this...or even if it's sensor related but I have my suspicions. Last week, coming west across I-78, hit a rather harsh bridge joint and a 10 amp fuse popped that went to my instrumentation. Tach & speedo quit indicating. All other gauges still operable. Dash/gauge lights dark. Miles did not register because '07 is digital. Pulled off, found blown fuse with test light, replaced...back to normal. Not sure if related to bridge joint jar but felt like it was. This week...speedo quit working (no bridge joint this time)...mileages, of course quit racking up too. Tach still working. All fuses down by the left foot are OK. I came on home but checking things on my way I discovered the cruise control will not engage. I do have the factory PTO switch just for reference. The PTO engages and disengages however it will not throttle up now by toggling the cruise switch and hitting the "set" toggle as it always did since new. So methinks it's connected somehow with the speedo issue. Another part of the puzzle and what might be telling is that I can raise & lower the idle by toggling the "Set-UP/DOWN" switch as normal on my Cummins powered 379. One more related (maybe) issue that began all at the same time...the engine brake has about a 8 second delay before engaging after removing foot off the fuel pedal where it was always immediate before. Speed sensor? I did get a warning on my Road Relay IV readout that said service the speed sensor circuit soon. That's pretty self-explanatory I know but...if there are no wiring issues (cut, broke, loose) can I safely assume it is the speed sensor itself? Also...is there only one sensor controlling this off the transmission? Last question...would the sensor be a Paccar exclusive or is it probably a Bendix/other piece that spans a lot of the other road trucks? Never any electrical issues prior... Thanks in advance.
10-4 speedo uses a diffrent speed sensor then the ecm some a duel head sensor some use two sensors you can get them at any truck supply store easy to change I always change them in pairs also check the trans output shaft for play
Thanks truckmechanic ! Apparently I've got the kind that uses one sensor because both cruise & speedo went at same time. My understanding was that the kind that use 2 sensors...1 is for speedo and 1 is for cruise. Where is it located? Back of transmission? I've narrowed it down to a Fuller part # K3454...I hope. Push in?
It's a push in with one 13 mm bolt holding it in if you look where the output yoke on the trans is it will be towards the top you will see the harness going to it
