speedo needle bounce

[Bevgeek]

Okay, hope to fit a new cable soon but today a new issue.
The usual bounce in the speedo needle got worse as the needle got to vertical - it suddenly dropped clockwise to hang limply facing south. Then it picked up again and continued the bouncy nature.
Any ideas apart from the obvious replacement cable.

[Lurch]

I wonder if there's a tutorial that someone's put on here covering Speedo stripdown and rebuild, mine could do with attention too, milometer not working, maybe a kind forum veteran could show a link..

[Big Jim]

Do you use the car regularly ? Mine had not moved for 7 years and the needle initially would fly from 0 to 70 and back again . With use it has now settled down to fairly normal .

[don58van]

Hi
If you search the web for something like "Smiths speedo repair" you will find a 'how to' pdf and a website with a little tutorial.

I think the flicking speedo needle will be because of gradually worsening cable condition. When the internal friction becomes really bad they stick and wind up internally until they either let go or snap.

The stuck odometer probably means that the pawl and gear that advance the numbers are damaged or sticky OR there is too much friction in the number reels.

Some minor rhythmic flicking of the needle is caused by the pawl pulling the odometer reels around.

Working on the speedo requires a reasonable amount of skill in working on delicate mechanisms.

[Lurch]

I'll look for the Speedo tutorial, I've successfully got a few old clocks working again so should be similarities, I can hear clicking so assume that's the mech trying to operate the milometer against whatever is stopping it.

[Bevgeek]

Yes, I will check out any speedo tutorials. There is no clicking so perhaps it may just be a worn cable.

[Trickydicky]

If you can't find the PDF online, pm me as I have a copy.

[Fingolfin]

In fairness, I fitted a brand new cable and have similar bouncing as before.

[don58van]

I fitted a brand new cable and have similar bouncing as before

Then the bouncing is probably stiffness in the odometer mechanism.

To explain--the drive to the odometer drums is not constant. Instead, every few revs of the speedo drive cable, an arm with a tooth on the end (the 'pawl') driven by that cable pulls a cog around that turns the drums. Excessive stiffness in that mechanism causes momentary extra drag on the drive cable--hence the bounce on the speed section of the instrument.

If your speedo has this problem, you will probably notice that the bounce is worse when the last digit is '9'. That is because not just one but the last two drums are being turned. It would probably be even worse when the last two digits are '9' because the last three drums are being turned. And even worserer ... you get the point.

Often odometers will fail completely when the last few digits are say '999' because the friction in the drums is just too high.

I hope this makes sense.

Don

[Fingolfin]

Don,
The odo turns freely between 9s and 0s, but that doesn't preclude what you're saying. I know my way around inside one of these speedometers - do you have any suggestions for how to minimize that kind of excessive drag?

[don58van]

The stiffness in these mechanisms is usually caused by the factory-applied lubricant becoming hard and sticky with age.

The only sure way I know is to take the whole mechanism apart, clean each piece and reassemble with a modest amount of light lubricant. This is a very tricky job.

As a quick and dirty fix, you could try squirting very small amounts of light lubricant between the drums and the exposed axle ends using a pressure can with a straw.

Don