For further clarification, most "control" cables are furnished from the factory
as
what is referred to as "prestretched". This is done to remove the
constructional
stretch referenced in my previous posting. If you replace the worn cable with
something from the hardware store: 3/16" 7x19 Galvanized A/C cable, you will
have to
make allowance for said constructional stretch -- or prestretch it yourself. A
3/16" cable has a nominal breaking strength of 4,200# -- the rated swl being
20% on
nominal or, in this case 840#. Prestressing is done by applying a load to the
rope,
in a straight pull, equal to 40% of the nominal breaking strength (1,680#). The
load is brought up gradually, maintained for a period of 5 minutes, relaxed and
repeated for a total of three intervals. It should then be placed into service
in a
reasonable amount of time. If you prestress it, coil it up and store for later
use,
it will return to its "as manufactured" condition.
Ed Hamilton
Edward Hamilton wrote:
> While I am new to this list serve (gaining info prior to my first purchase of
>a
> spitfire project), I can speak to the subject of cable stretch. The answer is
> yes.....actually two forms of stretch. First, there is constructional
>stretch,
> which amounts to the outer strands seating themselves about the core when
>placed
> into service or under load. This usually amounts to approximately 1/2 of 1%.
> This is followed by elastic stretch, over time, of an additional 3/10 of a %
>or
> so. In other words, total stretch would amount to a little over 1" per 10' of
> cable. Not having crawled under one as of yet, I don't know the total length
>of
> cable involved and/or the D/d ratios of any deflection sheave(s) that the
>cable
> may pass over
> Hope this is of some help.
>
> Ed Hamilton
> '?? Spite - not yet in my garage
>
> Zempel David wrote:
>
> > In finishing up the installation of my new brakes I attempted to adjust the
> > parking brake. It's never been adjusted correctly and only appears to be an
> > ornament attached to my TR4. It's impossible to adjust the cables that run
>to
> > the drums in that they are screwed as far as they can go into the "T" thingy
> > that connects them to the main parking brake cable. I imagine that once I
>add
> > brake fluid and bleed the brakes that this might take some of the slack out
>of
> > the cables. However, since the available adjustment (number of turns before
> > bottoming out) was almost non-existant, I'm not convinced bleeding the
>brakes
> > will solve my problem.
> > Do these 3/16" cables stretch? (I think that's unlikely)
> > Does anybody have a similiar experiance and solved it?
> >
> > thanks, Dave Zempel.
> > '63 TR4 Surreytop
> > Sunnyvale, CA.
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