Simultaneous Application of Gas and Brake Pedals

On Tue, 1 Feb 2005, Bernard farquart wrote:

> Anyone who thinks International Harvester products were *under*
> engineered has no concept of what they are talking about.

There is that, but I didn't pick on Putney for it 'cause his claim that
"AMC automatic transmissions" was crying out louder for attention.

They did have their downsides, chief amongst which was parts
interchangeability. Ever look at the Hollander Interchange Manual for just
about any "light duty" IH product? Six different and non-interchangeable
front brake drums for one model, for instance, depending on production
date!

But yeah, IH was never *ever* known for putting out marginally-engineered
products before the company failed and was reborn as "Navistar".

> I say this as the owner of a forty year old four cyl. scout that came
> factory with sodium filled valves, just because it seemed like the way
> to do it.

Yup. Very typical of IH.

DS

Nate Nagel wrote:
> Steve wrote:

>>
>> And the pedal effort in a 4400-lb 1969 vehicle with manual disk brakes
>> is NOT significantly higher than the pedal effort in a Honda Accord of
>> today. And disk vs. drum makes no difference at all. I just don't see
>> whay the staement that power boost "is a necessity with disk brakes"
>> keeps popping into discussions.
>>
>
> *sigh*
>
> I'm not typing my explanation of it again. It is far more likely to be
> necessary with discs than with drums. search this thread for it.
>
> nate
>

Nate, there's absolutely NO engineering basis for that statement! That
was my whole objection in the first place. The fact that there have been
several (incorrect) assertions made in this thread about "why" disk
brakes "need" power assist does not make it true. Disk brakes do not
"need" power assist any more than drum brakes, whether or not the drum
brakes are of the self-energizing variety.

Bernard farquart wrote:

>
> Anyone who thinks International Harvester products were
> *under* engineered has no concept of what they are talking about.
>

100% agreed on that one. The IH 345 is one of the most amazingly tough
engines I've ever seen. Pretty comparable overall to the
truck/industrial versions of the Mopar big-blocks of the 60s and 70s
(the 413 and 361 in particular).

Steve wrote:
> Nate Nagel wrote:
> > Steve wrote:
>
> >>
> >> And the pedal effort in a 4400-lb 1969 vehicle with manual disk
brakes
> >> is NOT significantly higher than the pedal effort in a Honda
Accord of
> >> today. And disk vs. drum makes no difference at all. I just don't
see
> >> whay the staement that power boost "is a necessity with disk
brakes"
> >> keeps popping into discussions.
> >>
> >
> > *sigh*
> >
> > I'm not typing my explanation of it again. It is far more likely
to be
> > necessary with discs than with drums. search this thread for it.
> >
> > nate
> >
>
> Nate, there's absolutely NO engineering basis for that statement!
That
> was my whole objection in the first place. The fact that there have
been
> several (incorrect) assertions made in this thread about "why" disk
> brakes "need" power assist does not make it true. Disk brakes do not
> "need" power assist any more than drum brakes, whether or not the
drum
> brakes are of the self-energizing variety.

So you're saying that all those years of engineering school and
experience actually working as an engineer with automotive braking
systems were for naught. The fact that you don't like my explanation
doesn't mean it's not true. Discs *do* require more line pressure for
a given brake torque than self-energizing drums, assuming similar
diameters and normal piston sizes. Simple, indisputable fact.

nate

(damn, I really hate it when I have to play the "credentials" card, but
willfully ignorant people just **** me the f**k off!)

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. 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.

Very true!

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

I don't like hydroboosts, just for the simple reason that a lot of
times the PS pump is not adequately sized. Thus, if you do a few quick
slalom maneuvers and then slam on the brakes, the pump may "gulp" for a
second to catch up. Not something that happens in everyday driving, to
be sure, but IMHO that makes it even more dangerous, as it can be
alarming when it happens.

I don't remember ever having this issue in my old BMW 535i but I've
experienced it in several light trucks and SUVs (only vehicles I've
driven with hydraulic assist.) Of course, the Bimmer had another issue
which was the hydraulic accumulator "bomb" was dead, which made initial
application of the brake pedal, um, interesting, but that was more due
to the fact that it was ancient and had 200K miles on it rather than a
design flaw. Likely with the dead "bomb" it would have experienced the
same problems, but I never had it on a test track to find out.

nate

On Tue, 1 Feb 2005, N8N wrote:

> Discs *do* require more line pressure for a given brake torque than
> self-energizing drums, assuming similar diameters and normal piston
> sizes. Simple, indisputable fact.

Definitely simple and indisputable, but why are you being so obtuse as to
pretend this is even close to half of the story? "Needs more line
pressure" does NOT necessarily equate to "Needs a power booster".

There are *many* ways of varying the mechanical advantage of the driver's
foot over the disc caliper pistons.

DS

On Tue, 1 Feb 2005, N8N wrote:

> > Hydroboost
>
> I don't like hydroboosts, just for the simple reason that a lot of
> times the PS pump is not adequately sized.

I don't like hydroboosts, for the simple reason that it's a doglick,
failure-prone, needlessly-complex system that gives rotten pedal feel.

In article . com>, N8N wrote:

>> Nate, there's absolutely NO engineering basis for that statement! That
>> was my whole objection in the first place. The fact that there have been
>> several (incorrect) assertions made in this thread about "why" disk
>> brakes "need" power assist does not make it true. Disk brakes do not
>> "need" power assist any more than drum brakes, whether or not the drum
>> brakes are of the self-energizing variety.

> So you're saying that all those years of engineering school and
> experience actually working as an engineer with automotive braking
> systems were for naught. The fact that you don't like my explanation
> doesn't mean it's not true. Discs *do* require more line pressure for
> a given brake torque than self-energizing drums, assuming similar
> diameters and normal piston sizes. Simple, indisputable fact.
>
> nate
>
> (damn, I really hate it when I have to play the "credentials" card, but
> willfully ignorant people just **** me the f**k off!)

A simple machine design textbook proves you're right nate. The self
energizing feature is the advantage of drums.

N8N wrote:
> Steve wrote:
>
>>Nate Nagel wrote:
>>
>>>Steve wrote:
>>
>>>>And the pedal effort in a 4400-lb 1969 vehicle with manual disk
>
> brakes
>
>>>>is NOT significantly higher than the pedal effort in a Honda
>
> Accord of
>
>>>>today. And disk vs. drum makes no difference at all. I just don't
>
> see
>
>>>>whay the staement that power boost "is a necessity with disk
>
> brakes"
>
>>>>keeps popping into discussions.
>>>>
>>>
>>>*sigh*
>>>
>>>I'm not typing my explanation of it again. It is far more likely
>
> to be
>
>>>necessary with discs than with drums. search this thread for it.
>>>
>>>nate
>>>
>>
>>Nate, there's absolutely NO engineering basis for that statement!
>
> That
>
>>was my whole objection in the first place. The fact that there have
>
> been
>
>>several (incorrect) assertions made in this thread about "why" disk
>>brakes "need" power assist does not make it true. Disk brakes do not
>>"need" power assist any more than drum brakes, whether or not the
>
> drum
>
>>brakes are of the self-energizing variety.
>
>
> So you're saying that all those years of engineering school and
> experience actually working as an engineer with automotive braking
> systems were for naught. The fact that you don't like my explanation
> doesn't mean it's not true. Discs *do* require more line pressure for
> a given brake torque than self-energizing drums, assuming similar
> diameters and normal piston sizes. Simple, indisputable fact.

True, but requiring more line pressure isn't the same thing as requiring
power assist. This is only true if the additional line pressure
required increases the pedal effort so much that a typical human hasn't
enough leg power to make them perform adequately. I don't think this is
the case across the board with disk brakes. I think that is the other
person's point.


Matt

Daniel J. Stern wrote:

> On Tue, 1 Feb 2005, N8N wrote:
>
>
>>Discs *do* require more line pressure for a given brake torque than
>>self-energizing drums, assuming similar diameters and normal piston
>>sizes. Simple, indisputable fact.
>
>
> Definitely simple and indisputable, but why are you being so obtuse as to
> pretend this is even close to half of the story? "Needs more line
> pressure" does NOT necessarily equate to "Needs a power booster".
>
> There are *many* ways of varying the mechanical advantage of the driver's
> foot over the disc caliper pistons.
>

True, but a lot of them involve tradeoffs, usually in the "stroke" of
the master cylinder. A smaller bore in the MC will provide good pedal
feel and acceptable pedal effort, BUT is not often workable in modern
braking systems as the pedal will eventually "bottom out" on a
full-effort, high-speed, ABS-active stop - definitely something you
don't want to happen. Likewise, there may not be enough room to leave
enough pedal left in a one-circuit-failed condition. Yes, it *can*
work, but there's plenty of reasons why it doesn't.

That said, in a light car (<2500 lbs.) I agree that a power booster can
probably be optional, although you probably won't see it with ABS for
reasons given above. Additionally, a litigation-sensitive corporation
isn't going to release a vehicle for production requiring *any*
higher-than-normal pedal effort unless it's a specialty model that
they're fairly confident is going to be bought entirely by enthusiasts.

nate

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