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From: hls on 16 Nov 2009 16:04

"Ray O" <rokigawa(a)NOSPAMtristarassociates.com> wrote in message Before
power assisted brakes were introduced, people
> routinely stopped vehicles by stepping hard on the brake pedal.

That is true, Ray, but also in those days we had front and rear drums, for
the most part.
Discs required a lot more pressure than drums, hence the power assist brakes
became
a necessity rather than just a luxury convenience.


From: someone on 16 Nov 2009 23:07
In article <sJWdnfF9FOHXI5zWnZ2dnUVZ_oKdnZ2d(a)giganews.com>, "hls" <hls(a)nospam.nix> wrote:
>
>"Ray O" <rokigawa(a)NOSPAMtristarassociates.com> wrote in message Before
>power assisted brakes were introduced, people
>> routinely stopped vehicles by stepping hard on the brake pedal.
>
>That is true, Ray, but also in those days we had front and rear drums, for
>the most part.
>Discs required a lot more pressure than drums, hence the power assist brakes
>became
>a necessity rather than just a luxury convenience.
>
>
i wonder about that. i don't think bikes are much different. it tales a lot
more pressure to stop my 650 triumph with a doubling leading shoe front than
a xt 750 jamaha, which had one disc front and weighs more.
From: dsi1 on 17 Nov 2009 00:09
someone(a)some.domain wrote:
> In article <sJWdnfF9FOHXI5zWnZ2dnUVZ_oKdnZ2d(a)giganews.com>, "hls" <hls(a)nospam.nix> wrote:
>> "Ray O" <rokigawa(a)NOSPAMtristarassociates.com> wrote in message Before
>> power assisted brakes were introduced, people
>>> routinely stopped vehicles by stepping hard on the brake pedal.
>> That is true, Ray, but also in those days we had front and rear drums, for
>> the most part.
>> Discs required a lot more pressure than drums, hence the power assist brakes
>> became
>> a necessity rather than just a luxury convenience.
>>
>>
> i wonder about that. i don't think bikes are much different. it tales a lot
> more pressure to stop my 650 triumph with a doubling leading shoe front than
> a xt 750 jamaha, which had one disc front and weighs more.

I doubt there's much validity that vacuum assisted brakes were required
because of the advent of disk brakes. My first car, a 67 Barracuda had
drums and vac boost, as did most cars of the time. That one had a tiny
V8 - a 273! Of course, today that would be a large engine - 4.5L. :-)
From: Ray O on 16 Nov 2009 16:28

"hls" <hls(a)nospam.nix> wrote in message
news:sJWdnfF9FOHXI5zWnZ2dnUVZ_oKdnZ2d(a)giganews.com...
>
> "Ray O" <rokigawa(a)NOSPAMtristarassociates.com> wrote in message Before
> power assisted brakes were introduced, people
>> routinely stopped vehicles by stepping hard on the brake pedal.
>
> That is true, Ray, but also in those days we had front and rear drums, for
> the most part.
> Discs required a lot more pressure than drums, hence the power assist
> brakes became
> a necessity rather than just a luxury convenience.
>
>

Among other things, pedal effort is a function of the design of the master
cylinder, difference in size between the master cylinder and wheel cylinders
(disc or drum), and pedal travel distance. The larger surface area of the
piston in a disc brake caliper relative to the surface area of the piston in
the master cylinder gives a mechanical advantage over the smaller surface
area of a drum brake wheel cylinder.

IMO, the biggest reason that it takes more pedal effort to brake on a
vehicle that was designed with power brakes and that has lost power assist
is that if the vehicle were designed to take minimal pedal effort without
power assist and then you add power assist, the brakes become very touchy
and difficult for most drivers to modulate. My dad's '67 Ambassador had
very touchy brakes, and in a panic stop, the passengers all got tossed
forward against their seat belts.
--

Ray O
(correct punctuation to reply)



From: hls on 17 Nov 2009 09:37

"dsi1" <dsi1(a)spamnet.com> wrote in message news:5eqMm.20048
> I doubt there's much validity that vacuum assisted brakes were required
> because of the advent of disk brakes. My first car, a 67 Barracuda had
> drums and vac boost, as did most cars of the time. That one had a tiny
> V8 - a 273! Of course, today that would be a large engine - 4.5L. :-)

Power assist brakes, as I said, became luxury items. They were not
absolutely necessary on drum brake cars, but certainly made braking
effortless. Finally they found their way onto almost every car.

Disc brakes on large American cars, without power assist, can be monsters.

It is just the way things evolved.
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