Simultaneous Application of Gas and Brake Pedals

On Fri, 28 Jan 2005 09:34:09 -0500, MoPar Man > wrote:

>Bill Putney wrote:
>
>> That's because of the "self-energizing" property of drum brakes.
>> The geometry of the pivot point is designed such that the small
>> amount of friction applied due to the pedal pressure gets amplified
>> by rotating the shoe into the drum harder (a multiplication effect,
>> a mechanical "power brake").
>
>I thought it was because the 100% of the pressure in the brake line is
>transfered to pushing both brake shoes into the drum (because the
>wheel cylinder is pushing 2 pistons outward towards the drum out of
>both sides of the cylinder) vs disk brakes (where half of the pressure
>is wasted by trying to force open the calipers and the other half is
>used to push the pads into the rotor).
You do not understand hydraulics.Pressure in a closed system is equal
and undiminished in all directions, and for every action there is an
equal and opposite reaction. ALL the pressure in a single ended OR
double ended cyl is exerted on the pistons.
Also, MANY early drum brakes were non-servo, or non self energizing
brakes. Huck (early GM) and centerline(early Chrysler) were not. Twin
leading shoe brakes of any description are not. The Bendix brake was
the first self energizing, or "servo" drum brake. Also known as single
leading shoe - the leading shoe contacts the drum first and jams the
trailing shoe firmly against the drum through the adjusting link (180
degrees from the cyl).
Brakes with fixed anchors opposite the cyl, or dual cyls, can NOT do
this.
>
>> The downside of power brakes, which is a necessity with disk brakes
>> because they do not have the designed-in mechanical amplification,
>> is that after one or two pumps of the pedal while under throttle,
> --------------------------------------------------------


>
>A condition I can't imagine happening in the field, unless it's one of
>these hypothetical mysterious run-away
>full-throttle-while-standing-still cases. Even in that case, you're
>not going to be pumping the brakes several times (and depleating the
>vacuum reservior) - you're going to plant your foot on the brake pedal
>and keep it there. In that case, you're not going to depleat the
>vacuum.


Don't bet your life on it.Several years ago (OK, mabee 15 or more) The
aftermarket cruise control on my wife's old Corolla wagon stuck at
half throttle. By the second attempt to slow it down,there was NO
vacuum left, She got around the "rolling roadblock" ahead of her and
allowed the vehicle to build some more speed, which reduced the engine
load and allowed vacuum to build again - meaning she had one more good
application in store. It was only a 1.8, but at 60MPH the brakes could
NOT bring the car to a stop with half throttle applied. To slow down
she had to shut off the engine, then restart it to keep going (to get
off the highway)

Just for kicks, I tried on my 94 TransSport 3.8 today. At 40kph, I hit
the brake and the throttle at the same time. Any reduction in speed
would be very hard to measure.On the second application without
lifting the throttle foot the vehicle sped up as I had less boost.
I only did a few seconds test, and the brakes were already starting to
smell pretty good. And this vehicle stops VERY well.

On Fri, 28 Jan 2005 11:29:07 -0600, Steve > wrote:

>Joe wrote:
>
>
>>
>> Both true. I've always found manual drum brakes quite capable. Detroit used
>> to make some cars with 300 gross hp, but not very many. Not like now! I
>> think cars today, on average, have more power than they ever had before, on
>> average. If you look at the big performers, of course it's far more obvious.
>> Several on the market with 400 hp, NET. Find a muscle car with that.
>>
>>
>
>The standardized methods by which horsepower is measured have changed
>MANY times over the years, not just the one big change (from SAE gross
>to SAE net) in 1972. The actual definition of SAE Net has been revised
>many times in the intervening years, as had SAE gross before that. Its
>meaningless to compare a 1969 "375 horsepower" 440 to a 2005 "350 HP"
>5.7 Hemi, except to run the two cars on the same dynomometer (or weigh
>them and run them down the dragstrip and calculate based on ET or trap
>speed- a surprisingly consistent and accurate method). Its quite popular
>now to dismiss the 60s ratings as over-optimistic, but having driven
>both old and new and having seen both old and new run on the same dyno
>is a real eye-opener. A lot of the 60s engines were actually
>deliberately under-rated because the insurance companies were trying to
>avoid covering high-horsepower cars.
Yes, many of the muscle car era cars were deliberately under-rated.
The SAE specs have changed some, but HP is still HP. The definition
has not changed. What HAS changed is the way HP is produced today.
The muscle car era engines put out prodigious torque at pretty low
speeds, many of them dropping off quite markedly above, say, 4000 RPM.

Today's engines, being smaller displacement, pruduce less torque, but
they continue, due to advanced tuning and design, to produce that same
torque, or very close, up into the 6000 RPM range and well above.
Since the formula for HP is lb-ft of torqueXrpm/5252, the horsepower
available from some of these "mighty mouse" engines is increadible .
You just have to wind them pretty tight to get it.

They do not give you quite the "seat of the pants" "grunt" the 455SDs
and street hemis, and 427 Shotguns, or 428 CobraJets did. Particularly
from a dead stop withouthigh-p-revving heroics.

On Fri, 28 Jan 2005, Steve wrote:

> Bill Putney wrote:
>
> > The downside of power brakes, which is a necessity with disk brakes
> > because they do not have the designed-in mechanical amplification,
>
> Why do people keep saying this?

The parrot effect, I'm guessing.

> Disk brakes DO NOT "require" power assist at all.

You are correct. They don't.

> I much prefer the feel of manual disk brakes to any other
> braking system out there.

Well, to be perfectly semantic about it, the only "manual brakes" out
there are the ones on vehicles specially modified for the handicapped. But
yes, I agree with you, a properly set up and dialled-in unboosted disc
system cannot be beaten in terms of pedal feel.

> 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. The car stops
> on a dime.

Unboosted discs are terrific in slick winter conditions, too. We're
looking at deleting the brake booster from my '92 Spirit R/T clone. It'll
doubtless take a different master cylinder, but there's an enormous
variety of MCs that'll fit.

I think the mistake most people make is in thinking that power brakes
without boost are the same as unboosted brakes. They're very definitely
not. The mechanical advantage of the brake pedal over the cylinder is much
greater in an unboosted setup than it is in a power setup.

DS

Daniel J. Stern wrote:
> On Fri, 28 Jan 2005, Steve wrote:
>
> > Bill Putney wrote:
> >
> > > The downside of power brakes, which is a necessity with disk
brakes
> > > because they do not have the designed-in mechanical
amplification,
> >
> > Why do people keep saying this?
>
> The parrot effect, I'm guessing.

Probably because the vast majority of disc brake cars do have power
assist - dating back to the first installation of modern discs on
American passenger cars in the '63 Studebaker models, where the disc
brake package came with a mandatory power booster.

>
> > Disk brakes DO NOT "require" power assist at all.
>
> You are correct. They don't.
>
> > I much prefer the feel of manual disk brakes to any other
> > braking system out there.
>
> Well, to be perfectly semantic about it, the only "manual brakes" out
> there are the ones on vehicles specially modified for the
handicapped. But
> yes, I agree with you, a properly set up and dialled-in unboosted
disc
> system cannot be beaten in terms of pedal feel.
>
> > 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. The car
stops
> > on a dime.
>
> Unboosted discs are terrific in slick winter conditions, too. We're
> looking at deleting the brake booster from my '92 Spirit R/T clone.
It'll
> doubtless take a different master cylinder, but there's an enormous
> variety of MCs that'll fit.
>
> I think the mistake most people make is in thinking that power brakes
> without boost are the same as unboosted brakes. They're very
definitely
> not. The mechanical advantage of the brake pedal over the cylinder is
much
> greater in an unboosted setup than it is in a power setup.
>
> DS

True, although with a reasonably heavy car it does become almost a
necessity to have the power booster because you are trading off pedal
travel against line pressure, and both need to be kept at a reasonable
level.

Personally the only car I've driven with unboosted discs was my '71
914/4, and the feel is spectacular...

nate

Daniel J. Stern wrote:

>
> I think the mistake most people make is in thinking that power brakes
> without boost are the same as unboosted brakes. They're very definitely
> not. The mechanical advantage of the brake pedal over the cylinder is much
> greater in an unboosted setup than it is in a power setup.
>
> DS

Absolutely, the pedal LINKAGE is often different in addition to a
different bore size in the master cylinder when comparing power brake
and non-power systems for the same model car. In the case of Mopar
B-bodies like my '69, the power brake cars had a bellcrank mechanism
that moves the master cylinder piston FASTER than the pedal moves. The
loss of leverage is more than offset by the power booster... UNTIL the
booster quits working and mashing the brake pedal is like stepping on a
block of lead. The manual brake pedal linkage is a direct connection
from the pedal to the MC piston and has much more mechanical advantage,
at the cost of more pedal travel. All other power brake cars have a
similar mechanism for reducing pedal travel, or simply attach the
pushrod closer to the pedal rather than closer to the pedal hinge
(another way of changing leverage)I LIKE the added pedal travel- for one
thing it makes "sudden acceleration" a lot less likely (just to tie two
threads in a knot... ) ;-p

wrote:

>
> Yes, many of the muscle car era cars were deliberately under-rated.
> The SAE specs have changed some, but HP is still HP. The definition
> has not changed.

I agree that 1 horsepower is still 746 watts, but that's where agreement
ends. If you could magically bring an LS-1 back through time and let GM
rate it in 1969 *exactly* the same way they rated the '69 302
smallblock, I think you'd be surprised how similar they are. Of course
the LS-1 can get 28 mpg in a Camaro, which the 302 never did.

> What HAS changed is the way HP is produced today.
> The muscle car era engines put out prodigious torque at pretty low
> speeds, many of them dropping off quite markedly above, say, 4000 RPM.

4000 RPM was right through mid 50s maybe. Even many big-block muscle car
engines of the 60s were good to 5000 to 5500 RPM. Not the long-stroke
monsters like the Olds 455, but quite a few others. Some short-stroke
engines like the Chrysler 383 could happily reach nearly 6000 RPM as
built in the 1960s. If I were to build a 383 with available
off-the-shelf pistons today, its simple to make it work beyond 7000 RPM.
And we all know that many of the 60s smallblocks were real screamers
too- Ford 283s and Boss 302s, Mopar 273s, and the Chevy 302 that was
good to nearly 8000 RPM come to mind

>
> Today's engines, being smaller displacement, pruduce less torque, but
> they continue, due to advanced tuning and design, to produce that same
> torque, or very close, up into the 6000 RPM range and well above.

No, they produce LESS torque up there, but since HP goes as the product
of torque and RPM (as you pointed out), they can produce similar
horsepower. Not necessarily MORE horsepower, but similar. There is only
a tiny percentage of production cars today that can produce the same
real-world horsepower as a Buick 455 Stage I or a Mopar 440. LS-1s do.
Vipers do. The 5.7 Hemi comes close, and the 6.3L Hemi (coincidentally
about 383 CID- aint that cute?) promises to do as well or better. Ford
Modulars don't (except the 32-valve Cobra which is about a tie). Only
the rather exotic BMWs and Benz's do.

What is true and what I think you're getting at is that the
garden-variety sedan V6 of today (say, a Chrysler 3.5 or a Buick 3.8)
produces more horsepower than a garden-variety 2-bbl sedan v8 of 1975.
But who really cares about that?


>
> They do not give you quite the "seat of the pants" "grunt"

Which is exactly what make them BORING.

In article > writes:
wrote:
>
>> On Sat, 22 Jan 2005 22:38:54 -0500, "James C. Reeves"
>> > wrote:
>>
>>
>>>Couldn't in my 1967 GTO. The engine torque far overpowered any brake
>>>pressure I could place on the brake pedal. Now the car wouldn't actually
>>>move (the front brakes kept it in place)...but it would sure billow plenty
>>>of smoke from the spinning rear tires!

I've seen a Dodge Aspen do this. True, it was a 1980 model police
package with the 360 4-bbl and a monster exhaust. It could be held
with the brakes and spin both back tires.
--
Jeff Wieland

Steve wrote:

> MoPar Man wrote:
>
>> I thought it was because the 100% of the pressure in the brake line is
>> transfered to pushing both brake shoes into the drum (because the
>> wheel cylinder is pushing 2 pistons outward towards the drum out of
>> both sides of the cylinder) vs disk brakes (where half of the pressure
>> is wasted by trying to force open the calipers and the other half is
>> used to push the pads into the rotor).
>
>
> You might want to stop and think about that... there is no "wasted"
> force in a disk brake caliper, either the single-piston "floating" type
> or the 4-piston "fixed" type.

Well, a self-energizing drum brake does take significantly less line
pressure than a disc to develop the same torque at the wheel... I'll
grant you that the explanation given above is inaccurate, but in a
typical disc with floating shoes and an anchor pin at the top, a lot of
the torque generated actually comes from the rotation of the drum
forcing the primary (trailing) shoe into the anchor pin.

nate

--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel

Steve wrote:

> Bill Putney wrote:
>
>
>> The downside of power brakes, which is a necessity with disk brakes
>> because they do not have the designed-in mechanical amplification,
>
>
> Why do people keep saying this? Disk brakes DO NOT "require" power
> assist at all...

I think it could be argued that for a commercially successful
main-stream consumer vehicle of today, they do.

> ...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, longer travel master cylinder
pistons to gain back some of that mechanical advantage. That comes at
the "cost" of much greater pedal travel, which has the upside of greater
sensitivity (i.e., being able to modulate the pedal more precisely).

I guess my comment was about what 95+% of people drive on the road
today. Apparently the mfgrs., for good or bad, feel that the public
wants short pedal travel for *perceived* quick reaction time and
*perceived* safety.


The car stops
> on a dime.
>
> And if that streetable example weren't enough, how do you explain the
> fact that no NASCAR race cars have a power booster, but they all have
> 4-wheel DISK brakes???

If there is no type of boost at all, then it is, by definition and the
laws of physics, at the price of longer pedal travel and the advantage
of greater control - again - by playing games with the master/slave
piston diameter ratios.

The reason that they don't have power boost is that (1) there is not
adequate vacuum to guarantee boost under all critical conditions, and
(2) The weight penalty of a separate electrically powered vacuum pump is
too high. The obvious solution for that niche application is to utilize
the adaptability and quick reflexes of the drivers and have a bonus of
greater sensitivity (modulation control) as a bonus.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

Daniel J. Stern wrote:

> On Fri, 28 Jan 2005, Steve wrote:
>
>
>>Bill Putney wrote:
>>
>>
>>>The downside of power brakes, which is a necessity with disk brakes
>>>because they do not have the designed-in mechanical amplification,
>>
>>Why do people keep saying this?
>
>
> The parrot effect, I'm guessing.

No. The reality of modern consumer vehicles that will be driven by
quite a range of ages, mental quickness, and physical strength.

I used to drive an International Travelall (similar in size to a Chevy
Suburban). Unfortunately the mfgr. figured it didn't need power
steering - but, man, you should have tried to parallel park that thing -
quit4e a feat even for a teenager. I think there would be similar
problems selling a modern vehicle with unpowered disk brakes as selling
ones without power steering just due to human factors.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')