Haywire Speedometer

[pgls651]

Hi Folks
On a Pete 579:
Recently I had the speedometer completely turn loose and erratically going from near zero to about the speed I was actually traveling (GPS indicated). The very first signs showed a slight movement away from the actual speed but got worse with ascents/descents and rough roads. At idle, zero speed there was no dial movement- stays at zero. And of course the cruise control cannot work. The speed sensor has been changed, and this seemed to work for a few hours or so until the problem came back with a vengeance. Any ideas of where to look next?

[marek4792]

Did you test the wiring? Does it change with the weather? How is the output shaft endplay? Tonewheel?

[pgls651]

No change with the weather. The speed gauge went from normal to erratic over time and aggravated along with grades or rough roads but currently goes haywire from the start. And testing wiring is a good next step. Maybe looking for a loose ground between sensor to speedo? Not sure how to check output shaft or tonewheel.

[pgls651]

No change with the weather. The speed gauge went from normal to erratic over time and aggravated along with grades or rough roads but currently goes haywire from the start. And testing wiring is a good next step. Maybe looking for a loose ground between sensor to speedo? Not sure how to check output shaft or tonewheel.

[Rawze]

tailshaft speed sensor is the first thing to check. After that, it is well known that speedo's in those 579's are flaky as h#ell and sometimes need replacing.