I chased down an A type this summer, I was actually looking for an annulus
for my 22/1712 which has 6 starts for a 15-tooth speedo drive. I found
several with 4 starts and 5 starts, only one with 6 which I had put on a
22/1711 unit that I got as a spare.
I don't know how much variation there is in the speedo gear take-offs or how
they tolerate to different start configs, but there are bits out there
66 TR4A CTC74217LO (soon to be reunited with the O/D)
Date: Wed, 4 Sep 2002 16:16:56 -0700
From: Randall Young <ryoung@NAVCOMTECH.COM>
Subject: RE: Rt angle speedo drive w/o 1:1 gearing?
> I worked out what was needed then rang ORS who told me I couldn't have
> what I wanted but that I could achieve the same ratio by other means
> i.e. not having a pinion that went as low as 17 teeth (I think) to go
> with the 6 start spiral but I could get 20 to go with the 5 start
> spiral. Basically I did it from informed advice of a supplier.
> There are many
> vehicles which use
> the Laycock OD unit, not only the LBC's but Volvo's and Ford Transits
> and others, so there are numerous alternatives for the speedo drives
> that are not listed in Triumph books.
BTW, A-type ODs do not have a replaceable spiral gear, it's built into the
annulus. AFAIK they only had one driven gear as well, basically the
standard at the time was to modify the speedo head to match the gear ratios
and tire sizes, the speedo cable was always driven at 2.5 times the output
shaft speed. J-types (and perhaps D-types) had the interchangeable spiral
gear and driven gear.
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