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Speedo drive connection
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Kleftiwallah



Joined: 27 Oct 2016
Posts: 222
Location: North Wiltshire

PostPosted: Wed May 30, 2018 1:52 pm    Post subject: Speedo drive connection Reply with quote

Good afternoon chaps.

Does anyone know the threadform on the inside of the brass knurled connector on the speedo drive, usually round the square drive?

After peering into the problem, I think it's 24 tpi and a core measurement of .435" (if that's any help).

7/16ths U.N.F. seems to do the trick, but could the thread be tapered internally?

Looking forward to your replies. Cheers, Tony.
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peter scott



Joined: 18 Dec 2007
Posts: 6179
Location: Edinburgh

PostPosted: Wed May 30, 2018 4:47 pm    Post subject: Reply with quote

Hi Tony,

I'm not sure of the size but I pretty sure it's not a tapered thread.

Peter
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MVPeters



Joined: 28 Aug 2008
Posts: 679
Location: Northern MA, USA

PostPosted: Wed May 30, 2018 6:20 pm    Post subject: Reply with quote

It might be easier to measure the outside of the speedometer head connection!

My Halda Speedpilot instruction sheet shows one speedometer cable with NF 5/8" x 18 connections - I think that's UNF - not tapered.
A 24-pitch thread would be 5/16 or 3/8 - quite a difference.
(The other cables are all metric M12 - M19 which I assume relates to foreign speedometers).

https://www.eaglefastener.net/technical/fine-thread.html

https://www.motalia.com/Html/Charts/unf_chart.html
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Kleftiwallah



Joined: 27 Oct 2016
Posts: 222
Location: North Wiltshire

PostPosted: Thu May 31, 2018 1:11 pm    Post subject: Reply with quote

Thanks for those useful answers, (even from the settlers across the pond)!

Thanks and Cheers, Tony. Smile
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Kleftiwallah



Joined: 27 Oct 2016
Posts: 222
Location: North Wiltshire

PostPosted: Thu May 31, 2018 7:22 pm    Post subject: Reply with quote

The teeny tiny screw was also missing that secures the 'bowden' cable to the speedo but with a careful threadmaking of 8BA on a piece of filler rod it fits a treat.

All I have to do now is re-thread a countersunk screw and we're away.

Cheers, Tony. Wink
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