Help with thread form on Simplex Rear Derailleur

[Losgaintir]

Can any Form member offer any advice, as to the correct thread form for the Fork End fixing screw, on a 1948-1950 Simplex Tour de France rear gear.
This goes through the Black hanger, which connects the gear to the rear drop out. And it is not metric!
Grateful for any help
Colin

 

[bagpuss]

Re:

French thread ?

 

[Losgaintir]

Re:

I wonder if an image might help jog memories?
Colin

 

[one-eyed_jim]

You're talking about part 503 here?

https://vintagebicyclerestoration.files ... ltered.jpg

I suspect it is metric, just not ISO. Old French bikes often use odd metric threads - 5mm x 0.75mm pitch, for example, rather than the common ISO M5 x 0.8mm.

 

[Losgaintir]

Re:

Yes, I agree.
It is part #503 on the Tour de France parts list.
Any idea where I might get more information on these older French non ISO threads?
Colin

 

[Losgaintir]

Measuring the thread on this wretched screw is a real pain.
Diameter no problem at 4.85 m.m.
Trying to measure the T.P.I. presents more of a .
Because of its shortness, one can only measure 1/4" of crests, then multiply the answer by 4.
Not very accurate, as any dicrepancy in the 1/4" measurement, is magnified by a factor of 4
Colin

 

[one-eyed_jim]

Don't you have a millimetre ruler?

:shock:

Pitch can be hard to judge by eye, but the likely candidates here are 0.5mm, 0.75mm and 1mm. It shouldn't be too hard to distinguish between them, even over a short length of thread (6mm, for example). It doesn't make any sense to convert from a metric pitch to tpi and back.

Alternatively, I suspect member bduc61 may be able to find you a definitive answer.

 

[Little Al]

IIRC It's a M5 Fine pitch. If really desperate the Bolt & the inner nut that fits in the dropout can be replaced as a unitone from an older Sachs unit seem to fit best

 

[VeloFellow54]

Re:

I have 2 (pre plastic pulley) Tour De France mechs. Both are threaded into the hanger and into the locknut. The look M5 to me - but - one has a coarse thread - the other fine. This mech was in production a long time and they produced millions (with many variations). Sorry - not much help I know, but best to be aware that there are variations

 

[Midlife]

If all else fails I guess you can buy a modern one?

http://www.amazon.com/Sunlite-Rear-Dera ... B000AO9QME

Shaun