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Re: Tail lenses

To: Chris Vaught <CVaught@hawaii.rr.com>
Subject: Re: Tail lenses
From: Steve Laifman <laifman@flash.net>
Date: Wed, 25 Aug 1999 08:02:46 -0700
Chris Vaught wrote:

>  My only real delima is in what size ti buy. 3/4,7/8, or 1" bore. What would 
>be
> best for the stock calipers and wheel cylinders? Would a 1" bore on the
> clutch reduce pedal effort? These are just a few of the many questions I
> have. If you have any ideas or past experience please let me know.
> Thanks
> Chris

Chris,

Don't know what will "fit" the dual thickness firewall mount, clearances, and
pedal connections, but you've got the diameters backwards.  The smaller the 
bore,
they less the pedal effort (with or without a servo) but the further the travel.
It is related to the ratio of the pedal force (use pedal lever arm lengths to 
get
foot force) and the area of the piston of the master cylinder.

Input force, for same output force,  is ratio of the square of the considered
diameters.

For instance:  a 3/4" cylinder is 0.5625 inches squared.
                    a 7/8" cylinder is 0.7656 inches squared.
                The ratio is 0.7656 divided by 0.5625, or 1.36

    For the same output pressure the 7/8 cylinder requires 1.36 times the input
force as the smaller 3/4" cylinder, and correspondingly less travel.

Other way round, 0.5625 divided by 0.7656 is 0.735  or 73.5% less force for the
3/4 over the 7/8 (and, of course more pedal travel.)

Sorry, but I don't know the pedal ratio, off hand, so you'll have to measure the
distances between the pedal and the hinge point and the hinge point and the 
master
cylinder attach hole.  The ratio of these numbers gives you the leverage of the
pedal to apply to get foot force and pedal travel.

Girling(/Lucas) cylinders are available in different bores and fit your 
mounting.
No real need to go elsewhere, as they are available.  You probably will have to
reuse your original pedal input yoke/shaft.

My son Jay has done some of this on his Alpine, when he removed the servos, so 
he
may have specific part numbers and results.  Of course, his legs are a good deal
stronger than mine.

The elimination of the power servo, alone, will increase your pedal forces from
2.3 to 3 times the power assisted forces, with no M/C change (depending on year
and PO substitutions of non stock units.)

You are, of course, limited by the floorboard, or you could move the firewall
FORWARD 4".

{9->

Steve

--
Steve Laifman         < Find out what is most     >
B9472289              < important in your life    >
                      < and don't let it get away!>

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