Smith's Speedo Cable Fitting?

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Tornado

Tornado

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I had my speedo off bike yesterday to replace the crusty glass. Got a new glass with Seals and bezel in a kit which also had fresh rubber grommets for the casting bolts.

Anyway got it back together but when fitting cable to the clock noted the ferrule wasn't sitting square and appears it has been cross threaded. This may be causing the jerkiness to the needle at most speeds.

Can anyone tell me the correct die size to use on the ferrule fitting?
 
It's metric M12 x 1.0.

(Edit: The speedo cable drive gearbox end is 1/2" x 26).
 
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FWIW, I rarely use "cutting" taps or dies on existing threads. i really prefer to use thread chasers. fleabay has small, affordable sets, and IMO, well worth the investment. i have several sets - covers most of my needs.

side note - i see the set shown does not include a M12-1.0 - ???. edit: I now see that the thread size is 1/2-26 - same would apply, however my set does not include a 26 tpi
Smith's Speedo Cable Fitting?
 
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Verify that your Speedo works ok by running with a drill set in reverse. That will tell you if the sticking is internal.
 
As 12x1 thread chaser dies are not commonly around and the metal is relatively soft you can use M6x1 tap as a thread file. It has the advantage over the chaser that you can engage good threads and use them to get the 1 or 2 top threads back into line, thread chasers follow the bad threads until they engage enough good ones, unless they are split first.
 
Thanks all for the replies. Would not have thought a British gauge manufacturer would use non-Christian measurements back in the '70s. ;-)
I'll be having a look in my metric tap and die set.
 
Tornado said:
Would not have thought a British gauge manufacturer would use non-Christian measurements back in the '70s.
Click to expand...

Goes back further than that as Smiths simply continued using the metric Chronometric cable thread.

http://velobanjogent.blogspot.com/2008/03/smiths-chronometric-speedometer-and_21.html
"The Chronometric speedometer is a principle commenced by the Jaeger speedometer company in Paris, France, in the 1920s and as such is a METRIC instrument, that is the dimensions, screws, threads etc are metric and not imperial as generally thought."
 
Getting a sharp die to start a thread like that can cause even more damage in my experience. What I have done in the past on soft metal was to get a wide nut of the correct size & thread, cut it in half (perpendicular to the threads ;)) then clean up the cut edges so there are no burrs. Place each half of the nut up above the damaged threads, place a tight fitting spanner or adjustable on the nut an wind it off, and the cut edges should clean up the thread on it's way off. And as they say on shampoo, repeat if necessary.


Cheers,

cliffa.
 
cliffa said:
Getting a sharp die to start a thread like that can cause even more damage in my experience. What I have done in the past on soft metal was to get a wide nut of the correct size & thread, cut it in half (perpendicular to the threads ;)) then clean up the cut edges so there are no burrs. Place each half of the nut up above the damaged threads, place a tight fitting spanner or adjustable on the nut an wind it off, and the cut edges should clean up the thread on it's way off. And as they say on shampoo, repeat if necessary.


Cheers,

cliffa.
Click to expand...
Thats a good method. I've sawblade cut slots perpendicular to threads on bolts or nuts to make them into thread chasers but I can see the advantage of placing a two-part nut beyond the damaged thread then winding it back over it. Will have a look in my metric kit for what I have and see if I can find a sacrificial nut somewhere.

On my test ride earlier today, the speedo calibration was checked vs gps and it's off roughly 5-10mph (hard to know more precisely with the jerkiness happen right now)....reading low WRT gps values...which is the more troublesome side of correct as it can lead to speeding tickets etc ;-)
Once I get the cable thread sorted and hopefully jerkiness cured, will have a go at calibration. What's the recommended method, pop the needle off the pin and re-place it with less tension of the wound spring to give a greater reading at a given cable rpm? Repeat until it's better?
 
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Got the thread cleaned up enough to allow the ferrule to engage squarely and then turn down more fully. Did the drill on the drive end of the cable to watched the speedo needle. Seems much better as far as jerkiness. Now this seems most apparent at very low end of scale and smooths out at 25+ mph reading. Definitely affected by bending of the cable if I wiggle the drill connection about.

Got a small hole bored into the casing cover to allow access to the brass calibration set screw as per the thread LAB posted above. Now its a matter of doing some test runs and tweaking that screw to match readout on gps. Apparently it is a clockwise turn (as viewed while looking up at underside of speedo) for a speedo reading lower than actual speed (my case).
 
In Victoria, when Jeff Kennett was Premier, he passed a law that speed cameras could not be disputed on the basis of calibration. So what would be the point in having an accurate speedo ?
 
Tornado said:
Got the thread cleaned up enough to allow the ferrule to engage squarely and then turn down more fully. Did the drill on the drive end of the cable to watched the speedo needle. Seems much better as far as jerkiness. Now this seems most apparent at very low end of scale and smooths out at 25+ mph reading. Definitely affected by bending of the cable if I wiggle the drill connection about.

Got a small hole bored into the casing cover to allow access to the brass calibration set screw as per the thread LAB posted above. Now its a matter of doing some test runs and tweaking that screw to match readout on gps. Apparently it is a clockwise turn (as viewed while looking up at underside of speedo) for a speedo reading lower than actual speed (my case).
Click to expand...
It's generally the cable/route of the cable that causes the jerkiness
I run an original Speedo and Speedo drive but I run it with an almost straight cable from the front wheel there is no waivering at all
Cheers
 
Yep the cable is usually the cause of wavering speedo needle. There is almost 6ft of cable. I tried a few ways to cure it and the thing that worked for me was -

Undo both ends and remove inner cable. Pour petrol down the outer cable to wash out all traces of old oil/grease/dirt/whatever. Clean inner cable with petrol too. Lubricate the inner cable as you feed it back in with some sort of dry lubricant. Don't lubricate the last few inches. I used some stuff that had Teflon in it which is sold for dry lubricating cycle cables. You should then have a rock steady speedo needle at any speed.
 
Nortoniggy said:
Yep the cable is usually the cause of wavering speedo needle. There is almost 6ft of cable. I tried a few ways to cure it and the thing that worked for me was -

Undo both ends and remove inner cable. Pour petrol down the outer cable to wash out all traces of old oil/grease/dirt/whatever. Clean inner cable with petrol too. Lubricate the inner cable as you feed it back in with some sort of dry lubricant. Don't lubricate the last few inches. I used some stuff that had Teflon in it which is sold for dry lubricating cycle cables. You should then have a rock steady speedo needle at any speed.
Click to expand...

I've used a graphite Aerosol that setup up dry before but have not done any proper cleaning out first. Will try that.
Regarding length, my cable seems a bit on the short side,esp as I turn the bars hard right, with speedo mounted left side. Cable seems to need every mm of length available.
The tacho mounted on right side seems to have too much cable and it needs to taken on a fair bit of snake bends to deal with excess. Is it better to run speedo on right tacho on left?
 
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