Simultaneous Application of Gas and Brake Pedals

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.

 

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.

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.

 

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.

 

The parrot effect, I'm guessing.

You are correct. They don't.

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.

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

 

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.

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

 

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

 

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.

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

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?

Which is exactly what make them BORING.

 

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.

 

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

 

I had a new 1975 Fuel injected Beetle when I was a kid.
There was no clutch lockout to start the vehicle.
My dad went to move the car cause it was blocking his car's access to the
garage in the driveway.
Temperature was below freezing, but not by a lot.
Throttle stuck open after he touched the pedal ( he was not used to fuel
injection cars and had "tapped" the gas pedal like a regular carb car to set
the choke for cold weather start.)
In gear the car was it started and raced through the garage door. ( remeber
1st and reverse are very low ratios )
Turns out the slush and snow build up had accumlated and frozen in the tube
that carried the throttle cable back to the engine.
So after he had "Tapped" the pedal partially, the cable remained stuck while
the pedal returned to normal (springloaded) position.

Even though it caught him by surprise he did hit the brakes but being in a
low gear the car (even tho it was a low horsepoer car - ie: a beetle)
managed to build up enough momentum to break through the garage door before
stopping.

In addition I have had several cars that have had momentary surges or
throttle sticks that required great effort to prevent catastrophe. I had a
66 Coronet with a transplanted 413 that once every three or four months
would race for no reason ( eventually I ditched that carter and got a
remanufactured one to solve the problem.

All I am getting at is there are a lot of reasons why something 'could"
interfer with fuel line, mechanical or electrical throttle body or
electronically controlled engines.

I think anyone who dismisses such a claim awithout fully investigating is
only furthering the mass hysteria often caused in the driving world by those
that don't know...

The poor man was honestly looking for an answer at the beginning of all this
and everyone seems to have taken the subject personally.

 

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

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

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')

 

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')

 

I guess I have to ask why you snipped the rest of that paragraph where I
essentially said exactly that. Continuing from where you snipped my
post: "...your vacuum reserve is depleted, and you essentially have no
(or extremely weak) brakes - this could become critical if a sudden
acceleration situation arises (due to driver error, floor mat jam, or
vehicle controls failure). The mechanics of the drum brake is totally
immune from that loss of amplification."

A person in such a panic situation is not only possibly going to pump
the brakes, but will very likely do so, only to find the brakes getting
very weak by the first pump, and for all intents and purposes, totally
gone by the second or third, and the remainder of the event, whatever it
turns out to be, will be over in mere seconds.

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

 

Obviously you meant "but in a typical drum with floating shoes..." 8^)

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

 

Bingo! An experiment that the naysayers refuse to try or don't want to
admit the results when they did. Under those conditions, by the second
or third pump, most boosted disc brakes are less effective than the
typical parking brake at slowing the vehicle down.

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

 

Sometimes I amaze myself. Sometimes even in a good way. Sometimes...
well, I just amaze myself.

nate

 

I don't understand the thinking behind that.

If you jam on the brakes, and you haven't locked up the wheels
(because you don't hear the tires squeeling), then why would the
typical person *let up on the brakes* and perform a second (or third,
etc) application?

In a panic situation where you know you haven't locked the wheels, I
bet the typical person would keep his foot planted on the brake pedal
until the desired degree of deceleration has been achieved.

 

Rawk! Yes.

Right, 'cause women and little old men *never* drove before what you
arbitrarily consider the "modern" age. Pfft.

No, the original owner decided it didn't need power steering. In any
event, that's irrelevant to the topic at hand, which deals with *brakes*.

Not hard enough, as it seems.

 

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.

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.

Hydroboost

 

Why would you pump the brakes if you were trying to stop a car with the
throttle stuck open?

Matt

P.S. To the owner of the TransSport, better get those brakes fixed.