After being plagued for too long with a speedo needle that would swing up to 180 degrees back and forth after a few minutes of riding I decided to try dealing with it. First, to determine for sure it wasn't the speedo itself, I disconnected the cable at the drive gear and pulled the cable out of the keeper so as to have the cable end up at waist height. Then I secured the cable end into my electric drill, on reverse setting, and ran it at various speeds to observe what the speedo needle was doing. At all speeds it was rock steady, so the problem was with the drive. With nothing to lose before trying to source a replacement, I shot 2 or 3 good squirts of 10w30 into the drive and reinstalled the cable. Next day, lo and behold the speedo operated properly for every minute of a 4-hour ride. Never having studied a drive unit up close, I can't say exactly how a bit of oil could result in a behaviour change or how long it will last, but for now it's all good. If or when it goes bad, I'll update.
Hmmm, mine is starting to bounce. Good to know.
Joe
FJ4ever,
A bouncing speedometer needle is often caused by a speedo cable that is bent sharply at some point. If you had bent the cable sharply while the drill motor was turning the inner core, you might have seen the needle bouncing again. The needle bounces because the core binds up at the curve, gets twisted physically, and then releases all at once. Cable bending and a lack of lubrication are probably the real causes of the problem. It sounds like your speedometer is okay, with just a bad cable bend or lousy lube in it. The cable drive at the wheel is a very unlikely cause.
Two likely fixes:
1. Disconnect the cable housing from the drive, slide the inner core out, and inject a little quality lube into the hollow housing (not a lot). Insert the cable core, and connect the cable to the drive. Use Ty-Wraps to secure the cable in a path that has NO sharp bends anywhere, just big gradual curves, to get to the speedometer. WD-40 is NOT a lubricant; it is mostly kerosene, and when the kerosene evaporates, you are left with a sticky mess.
2. Replace the speedo cable outright. They are cheap and available. Again, route the cable to the speedometer with NO sharp bends, using enough Ty-Wraps to keep the cable where it belongs. If the cable can slide downward, then the cable will become bent again, and the new cable will act like the old cable, causing a jumpy speedo needle.
.
The other cause to a bouncing speedo is the bearing surfaces inside the speedo wearing out. My speedo bounced for a time. Then it developed the Strangled Cat death howl. A little lube inside the speedo will work for a little while. But the lube will need to be replaced and eventually will not work at all. There is a company in San Diedo CA that will rebuild/repair our speedos, I will find the info and post it. Others have changed to aftermarket like Speed Hut GPS speedos. Very nice looking.
While you're in there... (http://www.fjowners.com/index.php?topic=17615.0)
FJ4ever,
Plan B:
Cheap USB GPS Speedometer.
https://www.amazon.com/VJOYCAR-Speedometer-Universal-Original-Motorcycle/dp/B07HQCCFWB/ref=sr_1_3?keywords=gps+speedometer&qid=1559708854&s=gateway&sr=8-3 (https://www.amazon.com/VJOYCAR-Speedometer-Universal-Original-Motorcycle/dp/B07HQCCFWB/ref=sr_1_3?keywords=gps+speedometer&qid=1559708854&s=gateway&sr=8-3)
.
Found it, here is the thread... http://www.fjowners.com/index.php?topic=15903.0 (http://www.fjowners.com/index.php?topic=15903.0)
Thanks for the comments. I neglected to mention that the first thing I had done was to replace the speedometer cable and ensure the new one remains well lubed and kink-free, so the cable isn't in play. We'll see how long a few squirts of oil can do the trick.
Update - after about 15 hours of post-squirt riding, the speedo is still working properly.
Update #2: A further 20-odd hours and the speedo is still giving me the right time of day, so to speak.
Update - now a year since trying this simple speedo fix, and it's still working fine. Haven't done anything to it since.