2nd Gen Non-Engine/Transmission erractic speedometer

[Hootguy]

Having issues with the speedometer,,,it will go up and down as i'm driving,,,causing transmission shiffting issues,,,is there a way of testing to find out if it's the speedo drive or the speedo itself. . for now,,i just uplugged the speedo at the trans and have no more shifting issues,,,using the GPS for speed,,,but i would like to fix this as soon as i can,,,anyone have any ideas???

These trucks have been around so long,,someones bound to have run into this before,,

Thanks

 

[charlessmith]

I think the Speedo and the Tach are both electric.

Somebody speak up here - I think the speedo is driven by a sending unit in the tail housing. Eh? If that's the case, it's probably a bad sending unit.

 

[Hootguy]

i realize the speedo is driven by a sensor in the transmission,,but i was hopping not to have to start throwing parts at it without knowing,,,,dont know if the speedo itself can go bad,,or if anyone has ever had a speedo go bad,,

 

[GAmes]

The speedo sensor is a small generator that drives the small electric motors in the odometer and speedometer needle. It is good that you disconnected yours. I let mine continue fluctuating and the electric pulses burned up the odometer motor and I had to replace the speedometer. More than likely your problem is the sensor. Before you remove it note how it is oriented. The gear shaft is slightly off center so rotating it allows gears of different diameters to engage the worm gear in the transmission. If you position it incorrectly either you won't get a reading or you will break the small internal driveshaft.

 

[Hootguy]

after 2 days of watching the speedo bounce up and down it was driving me crazy,,,and it would cause all kinds of weird downshifting at speeds on the highway... as soon as i unplugged the speedo the transmission issue went away,,and since i have a switch to manually turn on the OD and another switch for the lockup,,,truck runs just as good,,,