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RE: Master Cylinders

To: "Spridgets" <spridgets@Autox.Team.Net>
Subject: RE: Master Cylinders
From: "Larry G. Miller" <millerls@classic.msn.com>
Date: Tue, 21 Oct 97 17:57:37 UT
Reply-to: "Larry G. Miller" <millerls@classic.msn.com>
Sender: owner-spridgets@Autox.Team.Net
Chris

What it sounds like you are saying is that with all else being equal, the 3/4 
would require a longer stroke than the 7/8 to apply the same pressure. Is this 
is true, does anyone know the bore on the dual line master cylinders? Would 
there be any reason to switch to the dual line other then the dual lines? Does 
anyone know the reason the original switch was made from 7/8 to 3/4?  Was it 
because disks required less pressure than the drums to provide the same 
stopping power?, Or did it have something to do with the bore size difference 
between the calipers and the old wheel cylinders?

Larry



----------
From:   Chris Kotting
Sent:   21 October, 1997 10:36 AM
To:     'Larry G. Miller'; Spridgets
Subject:        RE: Master Cylinders

Though I haven't done a conversion (yet), and assuming that I'm following 
this thread correctly, basic principles of hydraulics say you should be OK 
going from the 7/8 bore master cylinder to the 3/4.

I'll try to explain.  Let's say you have a small diameter cylinder hooked 
up to a large diameter cylinder, and let's say for convenience that the 
small cylinder is 1" and the large cylinder is 2".  You stroke the small 
cylinder 1" by pressing on the brake pedal, exerting a force of 10 pounds. 
 The big cylinder will move 1/2", but will exert a force of 20 pounds. 
 Half the stroke, twice the force.  Larger differences in diameter change 
the ratio upwards.

The MGB calipers have bigger cylinders (also bigger pads) than the Midget 
calipers, hence with the same (7/8") master cylinder, more clamping force 
(and friction surface) on the brake disc, more stopping power for the same 
pedal pressure, at the price of a longer stroke (which might be okay if it 
gives you better "feel").  Going to the smaller (3/4") master cylinder, 
should make this effect more pronounced.

Does any of this make sense, or did I jump a tooth on my mental timing 
chain?

Chris Kotting
ckotting@iwaynet.net




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