Friend has a 91 B350 Wagon that is having issues with the speedometer. We replaced the VSS on the transmission and at first it would jump around at random speeds that were not correct for what the vehicle was doing. Like it would show 80 mph and we were not even doing 20 mph. Then two days later it started working correctly and now it seems to do what it want when it wants, it may read correctly or very randomly and sometimes not even at all.

What issues could be causing this type of problem?

 

Looked around and tripped over this. Search for "1991 dodge van odometer problem" to find a post in another forum by someone you will recognize. Apparently there is a gear in the speedo that will need replacing.

 

That gear is for the odometer. The speedometer was still working just the odometer quit. In this case the whole thing is acting wacky.

The only thing I did find was about resoldering the speedometer circuit board for it may have loosened up a few solder joints.

 

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