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I had my speedo rebuilt , new cable from vintage cables, new speedo drive. The needle bounces around. I sent quake back and it checked out fine. If you put a drill on the cable it fine. But going down the road it bounces.
67 tr6c

Is the rubber mounting ok?

Dave

This might seem a daft question, but is it hot where you are? I have found that my speedo needle bounces around when the weather's hot but is steady when it's cold. When it's really hot, there's no point looking at it - could be doing anything between 30 and 80!

Have you jacked the rear wheel off the ground and run the engine in gear to see if it bounces around? If it bounces I would guess you have an issue with your speedometer gearbox.

Have you jacked the rear wheel off the ground and run the engine in gear to see if it bounces around? If it bounces I would guess you have an issue with your speedometer gearbox.

I’ll try that. Thanks.

It’s only about 90!

I have read that if the inner cable is too long it could put pressure on the gauge causing the needle to bounce

I have purchased / used vintage cables (Smiths) from Canada and they are the highest quality cables on the market IMO...

Perhaps shoot them an email and see if they have any suggestions on this?

You say "only" about 90! That might be cool for Noo Joisey at this time of year but it's bloody hot where I live!

I had speedo rebuilt by the Portland Oregon guy. My speedo fluttered all over the place. He said to grind end of inner cable (shorten) to solve problem

Hi Morri, For sure too long a cable that binds in speedo head will cause needle bounce. How much does it bounce at what speeds?

Look at top end of cable & see where it seats on speedo. With cable hooked up at drive end measure how much cable is sticking up above the seat on cable housing. Record measurement. Now take a skinny flat blade screw driver & stick it up inside speedo head. Record that. Look at end of speedo. Do the math & see if your cable is too long into speedo head. Don't just grind as a guess.

Next feel how hard or easy the speedo turns using a flat blade screw driver. It should feel very free with only slight resistance.

Now hook cable to speedo head & remove it from the drive. Turn cable. It should still be quite free. The inner wire should turn with only slight resistance when screwed into speedo head.

It's unlikely the drive is faulty. In any case pump grease into speedo drive. Like 5 strokes of grease gun. Any excess will slowly ooze out over 100 miles or so. Will not cause any damage.

The cable must be well lubed. eBay sellers have dedicated cable lube which works good. However you can use wheel bearing grease smeared on wire, then a smear of motor oil to dilute & soften the grease. I know you're not supposed to lube upper 6-10" of cable, but I've found out of desperation the top bend just below speedo head can generate a lot of friction. I know your not suppose to lube the speedo bushing, but I've found 1-2 drops of 3 in 1 oil can work wonders.

Pretty much most vintage Triumph speedo needles wiggle to a degree, but only about 2-3 mph or less. Wild fluctuations are almost always friction winding up wire, then friction is suddenly overcome & cable unwinds suddenly causing needle to jump several miles per hour. First if falls as cable winds up, then raises as cable springs back. This oscillation gets magnified by momentum of the needle & magnetic cup.

Magnetic speedometers have a spinning magnet at the top of the shaft. There is an aluminum cup surrounding magnet. The cup is attached to bottom of needle shaft. As the magnet is rotated it generates a tiny electrical field in cup. The electrical field is magnetic. So this magnetic field is now being rotated around the spinning magnet pulling needle around. There is a small clock spring shaped return spring on needle shaft. Delicate stuff. So any oscillation of the spinning magnet must be removed.

My hunch is when spinning with drill it's smooth so needle is fine. But connecting cable you are getting binding at some point. So you need to experiment to find out where the binding is occurring. You are going to have to find the binding point.

The suggestion of running bike with rear wheel off ground is good. When doing this disconnect cable from speedo. Lightly grip the spinning cable end with finger tips & see if you can feel any oscillations of cable rotation.

One user found the cable was dropping too low & the square end could skip in speedo head. He ground down a nut as a spacer & slipped it over cable to raise cable end up. The cable wire can be pulled out.

If needed you can grind/file a spacer washer & put it on top of cable housing to move housing away from head or drive.

There is a cause for this, I know you have it inside you to find it. No question about that.
Don

I wonder if the inner cable on mine is just below too long unless heat causes it to expand, thus explaining why it only bounces the needle when the weather's really hot? I'll check the length as Don describes. It'll be great to fix this, and understand the cause.

TN - I've racked what's left of my brain for what could cause the symptom you describe, truly odd!
I would agree with Don that most wavering speedos (assuming speedo is healthy) are caused by the cable inner being restricted in its free rotation due to a kink or bend.
It may be that a bend is too tight or that the outer coils have been bent and distorted at some time. This is most often near the steering head.
Any such resistance to rotation of the inner will produce the "spring wind-up and sudden release" that Don has described. The greater the resistance, the more extreme the resulting fluctuation, and also will be shortening the life-expectancy of the gearbox and cable.
Manufacturers have used all manner of routings on various models, and this applies to control cables as well. Some routings chosen seem more for aesthetic tidiness than efficiency of cable operation. I prefer to run a rear wheel speedo cable in a smooth line under the engine up the front tube of the frame, with minimal kinks and a long curve. I also run my clutch cable in a similar fashion, though in this case it does look a little untidy because it "swoops" around (this is on a pre-unit so not relevant to this thread).
I'm doubtful that changes in ambient temperature alone could cause it, through expansion/contraction of the cable inner/outer, as there would need to be a much larger temperature differential between inner and outer to bring about differential expansion between (lengthways or diametrically) at different ambient temperatures.
TN - I guess you keep this bike indoors overnight. Say on a day like we've had lately, it has been pretty hot down here on the IoW, would your speedo be swinging from the moment you took the bike out? Or does it take a while to become a swinger?
I'm clutching at straws, but just wondering if its the intense sunlight heating up the greenhouse under the speedo glass causing the issue? In summer sunlight I can imagine very high temperatures developing inside the speedo case, if there happened to be a clearance in part of the mechanism that was particularly tight and susceptible to high temperatures, it could become tighter in its bush. Because under sunlight heating, the heating would be coming from the top face downwards through the mechanism, there would be a high temperature differential between the upper and lower drive components. It only requires sufficient expansion of one component to bring 2 discs that shoud have a tiny distance between them to too close for comfort, and cause malfunction.
I believe that you have several bikes? If so, could you try another speedo to see if it behaves the same? Many other experiments may be worth trying, for another time. Best of luck!

I have a 67 T120 and just disconnected the speedometer cable at the speedometer and measured how much the inner cable protrudes from the outer cable, it’s 7/16” yours should be close to that. Anything much longer could cause issues at the speedometer head, if the cable is to long I would check to see if the cable is fully engaged into the speedometer drive gear. Next I would get the rear wheel off the ground, crank the motor, put in gear, pinch the cable between your fingers and see if you have a smooth rotation of the cable if not then you probably have an issue with the gearbox or where the cable connects to the gearbox. You indicated in a earlier post the the speedometer worked OK when it’s attached to an electric drill, so that tells me that the cable and speedometer is eliminated from being a problem when not attached to the gearbox. It only happens when attached to the gearbox, so is the inner cable to long or is there a problem with the inner workings of the gearbox?

Exactly this, it will eventually bugger up the speedo. Other things to look at is cable lubrication and no sharp bends in its routing.
Also ensure the rear spindle is tight if using a rear wheel speedo gearbox.

After reading this thread I checked my speedo. I don't normally look at it much at slow speeds below 30 but noticed that the needle waggles at about 20mph and then is smooth after (I mean just the normal little tremble). Even though it is not across the scale could this also be cable related?

Dave

Thanks Koan, some good thoughts. The 'greenhouse effect' seems a strong possibility - stronger than the inner cable expansion idea I came up with, and for the reasons you've given. I could try a different speedo, and might do so. I think I'll measure the inner cable fit first though.

The speedo cable run is as smooth as I could make it. With all cables, smoothness of route is my top priority and, like you, I find it can make a real difference (especially with clutch cables). The cable isn't damaged or kinked.

That’s where I got the cable from.

Mori55 -
Several parts of your original post are unclear to me -

A) You bought a new cable from Vintage British Cables, who rebuilt the speedo? VBC or someone else?

B) Where did you get the new speedo gearbox? As far as I know, VBC doesn't sell them. Have you contacted the gearbox vendor?

C) What exactly did you send back and to whom? ("I sent quake back")

D) Have you contacted Andy Hansen of Vintage British Cables concerning the problem?

If not (D) suggest you do so. Andy has always sent a helpful response to questions I had.

Also, what prompted you to replace/rebuild speedo, cable, and gearbox in the first place? Wobble?

Speedo had pitted bezel scratched. The original gearbox had the inner part that was riveted came loose. I bought a repo gearbox from the bonneville shop. I can’t remember the company’s name in Oregon who rebuilt it. He also rebuilt a tach for me. Like I said I sent it back and he tested again and it was fine. When it gets below 99 degrees I’ll jack it up and test it out. I also have the original cable I can put back on.