Ooops ...
"So, for the same pedal pressure, with the 5/8" m/c you get about 43%
more force at the
slave cylinders or, conversely, to get the same stopping power you'll
have to press the
pedal 43% harder."
Should read:
So, for the same pedal pressure, with the 5/8" m/c you get about 43%
more force at the
slave cylinders or, conversely, to get the same stopping power WITH THE
3/4" CYL you'll
have to press the pedal 43% harder.
bs
Bob Spidell wrote:
> OK, I'll take a shot at this ...
>
> A 5/8" cylinder has a surface area of roughly .31 inch sq.
>
> A 3/4" cylinder has a surface area of roughly .44 inch sq.
>
> Let's say for illustration the force applied by your foot multiplied
> by the arm of the
> brake pedal is 100lbs (I have no idea if this is even close, but it's
> convenient).
>
> Divide 100 by the respective areas and get:
>
> On the 5/8" cyl the force applied to the brake fluid is roughly 323 psi.
>
> The force applied on the 3/4" cyl is roughly 227 psi.
> So, for the same pedal pressure, with the 5/8" m/c you get about 43%
> more force at the
> slave cylinders or, conversely, to get the same stopping power you'll
> have to press the
> pedal 43% harder. It's not the volume of fluid you push, but the
> force applied to it that
> matters (unless you have silicone brake fluid, which is apparently
> made from old sponges
> and is impossible for mortal man to bleed properly ;). The amount of
> pedal travel variance
> in the two would probably not even be noticeable (unless your slave
> cylinders are very far
> from the drums or disks, in which case you need to adjust your brakes).
>
> This is why the servo-boosted systems have the larger bore
> cylinders--the servo amplifies
> the foot pressure and you need less of the hydraulic advantage
> provided by the smaller bore
> master cyls.
>
>
> bs
>
>
> Steve B. Gerow wrote:
>
>> On my car the PO had fitted the .75 in. master cylinder which seems
>> to work
>> fine with my non-power drum brakes. The pedal effort is not up to modern
>> standards but not excessive.
>>
>> If I were to switch to the 5/8 cylinder would my pedal effort get
>> less or
>> more?
>> I'm thinking it would be less because I'd be moving the piston
>> further to
>> move the shoes the same distance.
>>
>>
>>
>
--
***************************************************************
Bob Spidell San Jose, CA bspidell@comcast.net
'67 Austin-Healey 3000 '56 Austin-Healey 100M
***************************************************************
|