Analog speedometer has some rather interesting issues...

Hey all,

The speedometer in my S12 has been acting really strange lately and I wanted a second opinion on it. When I'm driving the car will register a speed that is about double that of the actual vehicle speed, with random instances of it actually displaying the correct speed. I have to imagine this is a speed sensor issue and not a speedometer cable issue, but I wanted to make sure before I went out and hunted down another speedometer assembly. Please let me know your thoughts, thanks.

I will have to look when I get home, but don't think there's an actual sensor, rather a spinning cable that goes into back of speedo. In the last few years in really hot weather, mine reads about 5 mph slow after sitting in the sun for a few hours.
https://club-s12.org/forum/index.php/topic,38550.msg408068.html#msg408068

The speedo cable attaches on the transmission case and connects to the back of the cluster. Normal failures lead to a dead speedo when either the cable breaks inside due to corrosion or the plastic connection on the back of the cluster splits allowing the cable to rotate freely without driving the speedo. I'm not sure exactly how the cable is driven from inside the trans but one would think it engages with the transmission output because the gauge will register speed even while coasting. Reading 2x normal would not suggest a cable problem. Let me know if you should need another analog cluster.

Yea that's about what I thought was the case, I'm going to see to pulling the cluster some time this winter (I have a lot of other shit going on with this car so bear with me  :tongue2:) and Ill LYK if I'm in need of a new one. I was partially considering going to my towns watchmaker/ electronics repair store to see if they could diagnose the issue and repair it, but if that isn't an option then I guess new cluster it is.

I had the same issue many years ago.  I first took the cluster out and spray some silicone lube to the speedo but it made it worst so I used electrical circuit cleaner to degrease it and fixed it.  After a closer inspection there was a hairline crack on the plastic collar casing/cable attachment at the back of the cluster and I suspect some of the lube from inside the cable have gotten onto the back of the speedo.  I used some plastics model glue to fill the crack and wrapped the collar.  I also lube the speedo cable but using dry graphite used for lubricating locks.

Funny you say that, I pulled mine out of the car about a week ago and low and behold it had the exact same issue! When I pulled it I hadn't read your reply so I assumed the plastic collar was purely cosmetic and I just cleaned everything with isopropyl alcohol, when I get a chance ill try gluing that plastic collar back together like you did to see if that fixes my issue.

PS - Over the years gear oil had seeped up through my speedo cable into the cabin of the car, there was a solid 4 Oz of gear oil just chilling in the bottom of my dashboard, pretty wild huh?