Misc: Speedometers Speedo wheel gearbox

[vibrac]

Can someone tell me what ratio the wheel mounted speedometer gearbox should have? (spindle to cable turns)

 

[A Nut]

3 turns of the drive spindle gives 2 turns of the cable
Cheers
Brian

 

[A Nut]

P.S. What do you want a speedo for when racing?!

 

[vibrac]

P.S. What do you want a speedo for when racing?!

Rather than finding a replacement modern bike I am venturing into a twin for the road if I can build a machine from all the bits I have around me and sell all the bits I don't want I should finish up with a bike that can cope with today's traffic, have zero depreciation ,can side step all that eco nonsense and exclusion zones. And it will have a seat height I can cope with and a weight I can support , one thing for sure it wont have matching numbers and it wont be rivet standard and the death tax man wont be interested
Do you know I never bought 7.31 pistons before, well its a risk to exceed 80 on the road nowadays....

 

[vibrac]

3 turns of the drive spindle gives 2 turns of the cable
Cheers
Brian

Thanks Brian
OK thats what I have. The thread is about 30mm long which looks about right although I have one a bit longer
It still has its cardboard tube on the thread
I will have to make a housing does anyone know what the fine thread is on the aprox 18mm diameter is?
(thats one thread KTB missed

 

[oexing]

Vibrac, it´s Chronometric, not Chronoimperial. That thread is roughly M 18x1 mm and the other is M 12x1. I got that speedo drive from the Spares Co 30 years ago and found my taps did not quite match the Smiths gear, a tad too big. So carefully you can cut the drive for the correct M 18x1 if you like.
In fact no more use for that drive as I made my own angle gear from Dremel helical bevel gears when I finally decided to turn the homemade brake plates for better position on the Brampton. So the Smiths gear was too big to go on the bike. The Dremel type gear is slim enough to fit nicely. But yes, the Dremel gear is 1:1 , so now I will have to mod the Chronometric gears in the instrument for correct reading - if I ever care about this . . .

Vic

 

[vibrac]

Thanks Oexing 18mmX1mm is not difficult (good old Tracy tools) but one final worry before I proceed
the spindle in the brake plate turns anti clock wise when the bike goes forward looking down into the cable drive which way should that turn?

 

[oexing]

The cable is turning clockwise like the speedo hands. One of the reasons why I had no faith in ordering speedo drives from unknown sources as you can never be sure about what type you get.

Vic

 

[clevtrev]

Thanks Brian
OK thats what I have. The thread is about 30mm long which looks about right although I have one a bit longer
It still has its cardboard tube on the thread
I will have to make a housing does anyone know what the fine thread is on the aprox 18mm diameter is?
(thats one thread KTB missed

23/32 x 26TPI. The other one is 1/2" x 26 CEI.

 

[oexing]

When it is about fabricating a housing for the drive, you will want a tap obviously. Good luck finding a 23/32 x26 imperial. Not my idea, just chase the lightly oversize 18mm thread with a 18x1 die and have the tap for the housing. In the photo below the chased Smiths gearbox, perfect with the 18x1 thread.
We do not know what happened at Smiths half a century ago, they produced the Jaeger clocks approved by Jaeger. Seems they somehow felt for machining sort of close enough fancy threads not quite matching the original metric specifications. So with the 18x1 metric you just set things right after all that time . . .

Vic