dkinzer

The speedometer needle on my '91 LS400 was only partly illuminated so I bought a used instrument cluster on eBay to get parts to fix it. After examining the meter, I decided that the best course of action was to simply replace the entire speedometer mechanism with the one from the donor cluster. After re-assembling the unit and re-installing it in the vehicle, I took it out for a drive to see how it would work. I was elated to see that the needle was fully illuminated. So far, so good.

I had previously taken a couple of data points (RPM vs speed) so that I could get an idea of how close the replacement speedometer was indicating. Everything was looking good as I approached the first checkpoint speed of 45 MPH when suddenly the needle dropped so that it was hanging straight down.

Back to the shop I went to remove the cluster again and disassemble it. What I found was that the needle had somehow come loose from the meter shaft. I could press it down but it would pop back up with the slightest provocation. Needless to say, I was quite chagrined and not at all looking forward to spending $500 for a new meter from Lexus. I decided to try using super glue to afix the needle to the shaft.

After studying the old speedometer and noting the rest position of the needle (there appears to be a mechanical stop in the meter so the needle rests at 0 MPH), I carefully pulled the needle of the replacement meter outward as far as I thought I could do so safely and then applied some super glue to the shaft using a toothpick. Then, I rotated the needle slightly clockwise (perhaps 5-10 MPH), ensuring that the shaft did not turn also, and then pressed the needle down toward the face. When it bottomed, I rotated the needle counterclockwise, stopping at the previously noted rest position.

I then tested the movement by holding the meter so that its face was vertical and lightly flicked the needle clockwise. It came back to rest exactly at the intended position. Looking good so far.

After letting the meter sit for 30 minutes or so, I reassembled the cluster, reinstalled it and took it out for a second test drive. I noted that the needle sits almost exactly at 0 MPH when not moving and it matched the previously recorded RPM data points at 45MPH and 60MPH.

Just for fun, I installed the defective speedometer back into the donor cluster and reassembled it. Then I hooked it up to a 12 V battery expecting to see the half-illuminated needle. To my surprise, it was fully illuminated - as if nothing had ever been wrong. I rechecked the car to make sure the speedo needle in it was fully illuminated. It was.

This was odd. I left the donor cluster powered up for about 30 minutes and the speedo needle was still fully illuminated at that time. So now I'm baffled. Is it possible that a slightly corroded connection would cause a partially illuminated needle and that removing and replacing the connectors "cured" it?