Motorcycle Speedo not working

[Joel Hauser]

This is not a factory five, or even a car issue, but thought I would throw this out to our oh so knowledgeable community. I have a homebuilt 1968 Triumph 650 tiger that I built about 40 years ago, out of yard sale and swap meet parts. It has a smith speedo. the problem is the needle bounces around between 0 and 50, although the center of the bounce advances with the speed. I've put it on a drill and have the same bouncing problem. The cable is fine, well greased, not sticking, and spinning smoothly. the rear speedo drive is good.

I have already taken it apart - uh oh! - and have a million pieces on the work bench. I've cleaned up all the parts and think I can reassemble it. But before I do so, I thought I ought to think about what I'm looking for in terms of fixin' it. Has anyone ever actually FIXED one of these? What should I be examining? looking for?

Oh, and I purchased a new replica Smith Speedo on ebay; it arrived yesterday, and surprise surprise it doesn't work at all.

It would be nice to have a working speedometer.

[65 Cobra Dude]

My guess is to lubricate the cable with new grease and minimize the bends.

Henry

[Lickity-Split]

Could something like this be an option?

https://speedmotoco.com/kamikaze-moto-gps-speedometer-200kph-120mph-gauge-w-turn-signal-high-beam-lights/

[J R Jones]

Going inside a specialty part like a speedo, one should access, do I have the tools, knowledge and repair parts to fix this? You could get lucky and find something unattached, but failing that a technical expert is appropriate.
There are specialty shops to be found in Hemmings or Google, but I have found, through messaging, that replacement parts are often unavailable. That is my current problem with a 1991 radio.
If an internal part is the issue, and new replacement parts are not available, a specialist may have used speedos on hand to salvage parts from.
jim

[ggunter]

I like your choice in motorcycles, I have a restored 66 Bonneville. As for your speedo issue try lubricating the back of the head where the cable goes in. The inner shaft inside the head gets gummy and jumps when the cable turns it causing the needle to jump.I had the same issue with mine and WD40 fixed it.151129

[ggunter]

I should also note: does your cable have a nice square end and fit almost snug into the speedo head?

[ggunter]

All mechanical speedos operate with a magnet at the spindle inside the speedo which spins inside a disc which the needle is attached to. which usually has a slot cut in the disc or another magnet of the same pole and as the magnet of opposite pole pushes the needle along to increase speed. Being an old girl as she is the old lubrication gets gummy and makes things jump as the spindle tries to spin.

[Joel Hauser]

151172

Well, it's a little too late to send it to a specialty shop. And what's the fun in having someone else fix it? I'm going to clean up the mating and spinning magnetic surfaces, and make sure they are as flat as I can using 1200 grit paper. I'll clean and grease the cable. Maybe I'll get lucky? If not, I'll just put it back on the bike, and pretend it works. Thanks for your suggestions.

[Nigel Allen]

151172

Well, it's a little too late to send it to a specialty shop. And what's the fun in having someone else fix it? I'm going to clean up the mating and spinning magnetic surfaces, and make sure they are as flat as I can using 1200 grit paper. I'll clean and grease the cable. Maybe I'll get lucky? If not, I'll just put it back on the bike, and pretend it works. Thanks for your suggestions.

Just like the eggs that used to be in that carton, it looks scrambled to me :)

[Joel Hauser]

Well, that didn't work. I cleaned the spinning parts, put it all back together, greased the cable, reinstalled the speedo, and it's still bouncing around. At least I didn't waste too much time and money on this project.