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Old January 29th 05, 05:05 PM
Bill Putney
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Daniel J. Stern wrote:

> On Fri, 28 Jan 2005, Bill Putney wrote:
>
>
>>I think it could be argued that for a commercially successful
>>main-stream consumer vehicle of today, they do.

>
>
> Arguability and truth are not the same thing, and the former does not
> imply the latter.


We're talking about the market place - not subject to rigid rules as are
the laws of physics. That's why claims made about it are subjective.
Certainly you aren't going to claim that you can predict what the
"market" will do in response to some subtile technical change - yet
there likely will be a repsonse to that change. There's just no formula
to calculate the impact.

> Most consumers don't know or care what-all goes on under
> the hood and under the car. Give them a car that works (even marginally,
> viz. brisk-selling garbage from GM and Ford) and they'll buy it.
>
>
>>>...I much prefer the feel of manual disk brakes to any other
>>>braking system out there. My '69 Dodge currently has stock Kelsey-Hayes
>>>front disks and stock rear-drums, activated by a MANUAL disk brake
>>>master cylinder and a MANUAL pedal linkage. The feel is just wonderful,
>>>and really only slightly higher pedal effort than when it had a power
>>>booster, MC, and pedal setup. There is much more pedal *travel* which
>>>allows finer control over braking with the manual setup.

>>
>>Yes - achieved with much smaller diameter

>
>
> 7/8" bore vs. 1-1/32" bore, so the "much" smaller diameter amounts to a
> whole five thirty-seconds of an inch. And that's only on certain vehicles.
> In some years and on some vehicles ('70 and earlier A-bodies for one
> example), the same 1" bore was used with or without a booster.


So that's a 40% increase in piston area = 40% increase in
pedal-to-caliper piston force multiplication. Nice trick using a
throwing out a linear parameter in an attempt to minimize what is a
square law effect. 40% is a big difference when you're talking braking
effort.

>
>>The reason that they don't have power boost is that (1) there is not
>>adequate vacuum to guarantee boost under all critical conditions

>
>
> Hydroboost


Which does away with unobtainable vacuum requirements and gets the boost
from an "always on" source: the power steering pump. Thanks for
reinforcing my point that vacuum source for brakes is unreliable in
certain critical situations like stuck throttle, which is what I believe
we were talking about.

Once again, my points about the difference between drums and disc brakes
were in the context of the cars that 95+% of consumers and no doubt
those here drive. I stand by what I said.

The more commmercially viable vehicle will have power assisted disc
brakes on the front if not on all four wheels - right or wrong, that's
what today's market has determined. It has obviously not always been
that way, nor will it likely always be that way in the future.

>
>>(2) The weight penalty of a separate electrically powered vacuum pump is
>>too high

>
>
> Hydroboost



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Bill Putney
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