1990 Plymouth Grand Voyager Crazy Speedometer

My speedo just starting going nuts all of a sudden. When I am
driving, needle bounces from 0 to 120 mph. Where should I start
looking?

 

Speedometer sensor - It's on top the transmission, but you can only
reach it from below. Remove one bolt, pop it out, wipe the oil off
your face, and pop the new one in.

 

This vehicle has a mechanical speedometer, the sensor does not come
into play at all. A faulty speedometer would mean either the pinion
at the sensor, the cable, or the speedometer itself is faulty. Of
course, this did not come clear until after I purchased and installed
a replacement sensor ($80) as the first step in troubleshooting, with
no avail. In my case, it was the speedometer itself gone loco.

As reported, removing the cluster is really not that difficult. The
trickiest part is the shifter wire. The wire controlling the shifter
is removed by unclipping a metal retaining clip just under the
steering column, stretching the wire, and sliding it out from the slit
it is installed through. There is a little metal clip that is located
just behind this slit on the wire, keeping the wire in place. You
have to see this first hand to understand what is going on. Both
large round plugs come right off and there is a third square plug on
the right side. The speedo cable is also back there and may come off
with a good yank, otherwise, the panel under the steering column must
come off, arm shoved into the general area near the center of the
cluster, and forced off, feeling your way around.

After I removed the cluster and took off the front face, I was able to
remove the speedometer and inspect it. I inserted a small metal rod
into the speedo cable hole and was able to replicate the crazy speedo
performance (jerkiness, needle going to 125mph, etc). The odo would
still not work. I then sprayed a good deal of electronic lubricator,
this stuff is used for sliding switches and the like, doesn't harm
plastic, and allegedly lubes. I sprayed it up into the incoming
speedo cable area and all of the small plastic gears and voila, the
"dinging" noise disappeared, the speedometer began behaving naturally,
and the odo began to turn.

I put it all together and went for a test drive, put about 10 miles on
it at various speeds. It appears to now work normally, with the
exception that the "dinging" sound reappears occassionally at speeds
above 45 mph. If this turns out to not work, I'll get another cluster
or speedometer and put this problem to rest for good.

Thanks all for your help. I'll probably be back shortly with
something else gone wrong on this vehicle, it is going to make a
master mechanic out of me, it is.