Toby, et al:
OK - I whipped up a spreadsheet comparing force output at the wheel cylinders
over a range of input force values at the master cylinder, given the bore
diameters of the front wheel cylinders, rear wheel cylinders and master
cylinder. Including the range of rear wheel cylinder bore diameters yields a
good comparison of the relative braking force obtained from different sized
rear wheel cylinders. The calculation sheet
shows very clearly how the front brakes are applying much more force than the
rears, but figuring out exactly what it all means as regards a comparison of
the amount of braking force you're actually getting at each end of the car is a
different matter, precisely because of the factors you mentioned: differences
in swept area and the presence of the servo effect in the rear drum. Maybe a
little more digging into some of
the reference books is in order here...
Gary McCormick
San Jose, CA
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Toby B wrote:
> Actually,
> since the master cylinder bore's the same diameter for both circuits,
> it's the wheel cylinders that compensate for the different types of
> brakes! (Drums vs. disc) And wheel position (front vs. back) too. The
> contact area of the disc pad's a few square inches, compared to the many
> square inches of the shoe in back (and that's discounting servo action,
> which acts as an assist for drum brakes using the wheel's rotation). So
> the big calipers squeeze the front pads hard, while the rear cylinders
> push with much less force.
> And that junction block that connects both circuits is just a warning
> switch- there's no proportioning valve in the roadster, unlike many
> other cars...
> So it's really a pretty straightforward system!
> Toby
>
> Gary McCormick wrote:
> >
> > Thomas-
> >
> > So I am thinking that the tandem master cylinder (like on my '70 2000)
>provides a balance between the front and rear brake; that is, the two circuits
>(or whatever) are sized to compensate for the difference in slave (wheel)
>cylinder diameters and therefore displacement volume, front and rear ;
>allowing balanced braking (per the design intent of the engineer who laid out
>the braking system). Have I got that right?
> >
> > Gary McCormick
> > San Jose, CA
> >
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