Brake pad question



"wle" <[email protected]> wrote in message
news:[email protected]...
> "Mark South" <[email protected]> wrote in message
news:<[email protected]>...
> > Today I exeperienced something new to me.
> >
> > About 20 km into my Sunday morning ride, I was coming up
> > a gentle hill into
a
> > tiny village and thinking "Hell, I must be getting
> > weaker every day, why is
this
> > incline so hard?"
>
> well, after all that, what was it?

Good question. I still am not certain, but it seems to me
that my original explanantion based on thermal expansion of
the brake pads was the correct one.

When the bike is left in my cool garage overnight the brake
develops a little more travel and this reduces again when
I'm out on the road.

I run the pads very close to the rim to start with, so it
didn't take much to make them bind, I guess.
--
"Since you must keep improving, a $5 bike offers a lot more
opportunities to improve it, and can be improved cheaper.
It's expensive to improve on a $2000 bike." - Rick Onanian
in rec.bicycles.tech
 
I am betting it's dirty calipers that are sticking. I have noticed that my dual pivots "gunk up" a lot more often than my old single pivots.
 
Mark South writes:

>>> Today I experienced something new.

>>> About 20 km into my Sunday morning ride, I was coming up
>>> a gentle hill into a tiny village and thinking "Hell, I
>>> must be getting weaker every day, why is this incline so
>>> hard?"

>> well, after all that, what was it?

> Good question. I still am not certain, but it seems to me
> that my original explanation based on thermal expansion of
> the brake pads was the correct one.

Thermal expansion, even in soft material like bicycle brake
pads cannot take up that clearance unless they were dragging
after they were last adjusted.

> When the bike is left in my cool garage overnight the
> brake develops a little more travel and this reduces again
> when I'm out on the road.

> I run the pads very close to the rim to start with, so it
> didn't take much to make them bind, I guess.

You must be running with less than 0.5mm total clearance for
that to go away thermally but then you didn't comment on
whether the brake was off center (more clearance on one side
than the other). Dual pivot brakes cannot swivel except
permanently, by rotating the anchor bolt. That is what I
think happened. Somewhere along the way the brake caliper
got pushed to one side.

Check how easily the caliper and bolt can be rotated bolt
with the wheel removed. It should not be movable by hand if
the bolt is tight. If this brake is operating with less than
0.5mm clearance it is set too closely and will drag even if
perfectly centered when pedaling standing on hills. When the
bottom of the wheel is side loaded to the right, the top
moves to the right also and will cause drag.

Wheel flex of rear wheels in climbing is why Campagnolo
reverted to a single pivot, lower mechanical advantage brake
for the rear with more clearance. Such a brake does not need
to be dual pivot. Clearance is governed by how high the
mechanical advantage. Car disk brakes, for instance, run
with practically no clearance and have a high mechanical
advantage that is still too low without power assist. At
least their brakes have float to accept elastic movement of
the wheel and disc.

Jobst Brandt [email protected]
 
[email protected] wrote:

> ...Car disk brakes, for instance, run with practically no
> clearance and have a high mechanical advantage that is
> still too low without power assist....

The only reason for power assist brakes in a car of
reasonable mass would be to assist a driver with physical
disabilities. If people find non-assisted brakes too hard to
use, then they are either weak or lazy. This is similar to
finding a bicycle frame pump too hard to use. ;)

--
Tom Sherman – Quad City Area
 
Tom Sherman writes:

>> Car disk brakes, for instance, run with practically no
>> clearance and have a high mechanical advantage that is
>> still too low without power assist...

> The only reason for power assist brakes in a car of
> reasonable mass would be to assist a driver with physical
> disabilities. If people find non-assisted brakes too hard
> to use, then they are either weak or lazy. This is similar
> to finding a bicycle frame pump too hard to use. ;)

I suggest you test your hypothesis by shutting off the
engine of your car on a safe stretch of road and see how
easily you can stop it by stepping on the brake pedal. That
is what no-assist would be. Of course if you are driving one
of the 650,000 recalled Mercedes-Benz cars with electronic
control, you won't have any rear wheel brakes anyway.

The spongy response that is variable with dynamic pad
clearance from cornering is undesirable and has too much
travel due to the mechanical advantage in such systems. I
drove my last disc brake car with no assist long ago and it
didn't weight as much as the cars we normally use.

Jobst Brandt [email protected]
 
[email protected] wrote:

> Tom Sherman writes:
>
>
>>>Car disk brakes, for instance, run with practically no
>>>clearance and have a high mechanical advantage that is
>>>still too low without power assist...
>
>
>>The only reason for power assist brakes in a car of
>>reasonable mass would be to assist a driver with physical
>>disabilities. If people find non-assisted brakes too hard
>>to use, then they are either weak or lazy. This is similar
>>to finding a bicycle frame pump too hard to use. ;)
>
>
> I suggest you test your hypothesis by shutting off the
> engine of your car on a safe stretch of road and see how
> easily you can stop it by stepping on the brake pedal.
> That is what no-assist would be. Of course if you are
> driving one of the 650,000 recalled Mercedes-Benz cars
> with electronic control, you won't have any rear wheel
> brakes anyway.
>
> The spongy response that is variable with dynamic pad
> clearance from cornering is undesirable and has too much
> travel due to the mechanical advantage in such systems. I
> drove my last disc brake car with no assist long ago and
> it didn't weight as much as the cars we normally use.

I have driven older cars without power brakes and did not
find the effort excessive: certainly nothing out of the
normal range for fit cyclist. Brake boosters (in most
cases) change the feel of the brakes in a manner that
makes modulation more difficult. Power brakes (in a
reasonably sized vehicle) are no more necessary that power
steering is. [1]

[1] I used to drive a 1972 Oldsmobile with a broken power
steering pump. That car had close to 3000 pounds of
weight on the front wheels. At the time I weighed less
than 140 pounds and certainly DID NOT have above average
upper body strength.

--
Tom Sherman – Quad City Area
 
On Sat, 19 Jun 2004 02:29:41 GMT,
[email protected] wrote:

>Tom Sherman writes:
>
>>> Car disk brakes, for instance, run with practically no
>>> clearance and have a high mechanical advantage that is
>>> still too low without power assist...
>
>> The only reason for power assist brakes in a car of
>> reasonable mass would be to assist a driver with
>> physical disabilities. If people find non-assisted
>> brakes too hard to use, then they are either weak or
>> lazy. This is similar to finding a bicycle frame pump
>> too hard to use. ;)
>
>I suggest you test your hypothesis by shutting off the
>engine of your car on a safe stretch of road and see how
>easily you can stop it by stepping on the brake pedal.
>That is what no-assist would be. Of course if you are
>driving one of the 650,000 recalled Mercedes-Benz cars
>with electronic control, you won't have any rear wheel
>brakes anyway.
>
>The spongy response that is variable with dynamic pad
>clearance from cornering is undesirable and has too much
>travel due to the mechanical advantage in such systems. I
>drove my last disc brake car with no assist long ago and it
>didn't weight as much as the cars we normally use.
>
>Jobst Brandt [email protected]

Dear Jobst,

Gotta go with you on this one. I just peeked at an ancient
Subaru site devoted to elderly light-weight vehicles

http://www.cars101.com/oldsubaru.html#1983%20Subaru

Even in 1975, the first 1-ton Subarus all had power-assisted
front disc brakes. Despite their feeble 1.3, 1.4, and--gasp!--
1.6 liter engines, it was thought wise to borrow engine
power to help the brakes stop the thundering behemoths.

Oddly, the site says only that my state-of-the-art dog-
hauling 1983 Subaru has "vented" front discs and remains coy
about whether they are assisted by the pavement-rippling
1.8 liter 73-horsepower engine.

Carl Fogel
 
Tom Sherman writes:

>>>> Car disk brakes, for instance, run with practically no
>>>> clearance and have a high mechanical advantage that is
>>>> still too low without power assist...

>>> The only reason for power assist brakes in a car of
>>> reasonable mass would be to assist a driver with
>>> physical disabilities. If people find non-assisted
>>> brakes too hard to use, then they are either weak or
>>> lazy. This is similar to finding a bicycle frame pump
>>> too hard to use.

>> I suggest you test your hypothesis by shutting off the
>> engine of your car on a safe stretch of road and see how
>> easily you can stop it by stepping on the brake pedal.
>> That is what no-assist would be. Of course if you are
>> driving one of the 650,000 recalled Mercedes-Benz cars
>> with electronic control, you won't have any rear wheel
>> brakes anyway.

>> The spongy response that is variable with dynamic pad
>> clearance from cornering is undesirable and has too much
>> travel due to the mechanical advantage in such systems. I
>> drove my last disc brake car with no assist long ago and
>> it didn't weight as much as the cars we normally use.

> I have driven older cars without power brakes and did not
> find the effort excessive: certainly nothing out of the
> normal range for fit cyclist.

What "older cars" did you drive that had unassisted
disc brakes?

> Brake boosters (in most cases) change the feel of the
> brakes in a manner that makes modulation more difficult.
> Power brakes (in a reasonably sized vehicle) are no more
> necessary that power steering
> is.[1]

I think you are mistaking the poor response of drum brakes
for power disc brakes. Todays disc brakes are as linear and
controllable as you can expect, far better than brakes
without power assist.

Drum brakes got by without power assist for a long time
because drums use self servo (self activating leading shoes)
whose effectiveness varied with temperature and humidity, so
much so that they locked up on occasion. The non-linearity
of drum brakes is what got rid of them. Discs in contrast
are linear (braking proportional to pedal pressure) but
because they have a low coefficient of friction that, except
for the lightest cars, require a brake booster. These
boosters are vacuum driven in most cars.

> [1] I used to drive a 1972 Oldsmobile with a broken power
> steering pump. That car had close to 3000 pounds of
> weight on the front wheels. At the time I weighed less
> than 140 pounds and certainly DID NOT have above
> average upper body strength.

So what are you proposing? How does this affect brakes?

Jobst Brandt [email protected]
 
In article <[email protected]>,
[email protected] says...
> Tom Sherman writes:
>
<snip>
> > I have driven older cars without power brakes and did
> > not find the effort excessive: certainly nothing out of
> > the normal range for fit cyclist.
>
> What "older cars" did you drive that had unassisted
> disc brakes?
>
VW beetles from the late 60's early 70's. Porsche 911/912
from introduction (64) until quite recently (late 80's?)

> > Brake boosters (in most cases) change the feel of the
> > brakes in a manner that makes modulation more difficult.
> > Power brakes (in a reasonably sized vehicle) are no more
> > necessary that power steering
> > is.[1]

Porsche factory said this re the 911 for a long time.
>
> I think you are mistaking the poor response of drum brakes
> for power disc brakes. Todays disc brakes are as linear
> and controllable as you can expect, far better than brakes
> without power assist.
>
> Drum brakes got by without power assist for a long time
> because drums use self servo (self activating leading
> shoes) whose effectiveness varied with temperature and
> humidity, so much so that they locked up on occasion.
> The non-linearity of drum brakes is what got rid of
> them. Discs in contrast are linear (braking proportional
> to pedal pressure) but because they have a low
> coefficient of friction that, except for the lightest
> cars, require a brake booster. These boosters are vacuum
> driven in most cars.
>
Porsche customers said this for even longer - they won!
 
[email protected] wrote:

> Tom Sherman writes:
>
>
>>>>>Car disk brakes, for instance, run with practically no
>>>>>clearance and have a high mechanical advantage that is
>>>>>still too low without power assist...
>
>
>>>>The only reason for power assist brakes in a car of
>>>>reasonable mass would be to assist a driver with
>>>>physical disabilities. If people find non-assisted
>>>>brakes too hard to use, then they are either weak or
>>>>lazy. This is similar to finding a bicycle frame pump
>>>>too hard to use.
>
>
>>>I suggest you test your hypothesis by shutting off the
>>>engine of your car on a safe stretch of road and see how
>>>easily you can stop it by stepping on the brake pedal.
>>>That is what no-assist would be. Of course if you are
>>>driving one of the 650,000 recalled Mercedes-Benz cars
>>>with electronic control, you won't have any rear wheel
>>>brakes anyway.
>
>
>>>The spongy response that is variable with dynamic pad
>>>clearance from cornering is undesirable and has too much
>>>travel due to the mechanical advantage in such systems. I
>>>drove my last disc brake car with no assist long ago and
>>>it didn't weight as much as the cars we normally use.
>
>
>>I have driven older cars without power brakes and did not
>>find the effort excessive: certainly nothing out of the
>>normal range for fit cyclist.
>
>
> What "older cars" did you drive that had unassisted
> disc brakes?

I have driven various MG's and Triumph's with unassisted
front disc/rear drum brakes. Admittedly these car are
significantly lighter than today’s porkers (where a midsize
sedan can weigh 2 tons), but the braking did not take an
unusually high effort.

>>Brake boosters (in most cases) change the feel of the
>>brakes in a manner that makes modulation more difficult.
>>Power brakes (in a reasonably sized vehicle) are no more
>>necessary that power steering
>>is.[1]
>
> I think you are mistaking the poor response of drum brakes
> for power disc brakes. Todays disc brakes are as linear
> and controllable as you can expect, far better than brakes
> without power assist.
>
> Drum brakes got by without power assist for a long time
> because drums use self servo (self activating leading
> shoes) whose effectiveness varied with temperature and
> humidity, so much so that they locked up on occasion.
> The non-linearity of drum brakes is what got rid of
> them. Discs in contrast are linear (braking proportional
> to pedal pressure) but because they have a low
> coefficient of friction that, except for the lightest
> cars, require a brake booster. These boosters are vacuum
> driven in most cars.

Having driven 135,000+ miles in cars with 4-wheel disc
brakes and power assist but no anti-lock, I feel that I am
quite familiar with that type of system. I have also driven
plenty of pickups and vans with rear wheel drum brakes, so I
am all too aware of their poor modulation and "self-
energizing" effect.

>>[1] I used to drive a 1972 Oldsmobile with a broken power
>> steering pump. That car had close to 3000 pounds of
>> weight on the front wheels. At the time I weighed less
>> than 140 pounds and certainly DID NOT have above
>> average upper body strength.
>
> So what are you proposing? How does this affect brakes?

The point is that power assisted braking and steering (not
to mention automatic transmissions) are used in cars because
they are designed for lazy people who expect to put out no
effort, not out of necessity.

--
Tom Sherman – Quad City Area
 
On Sat, 19 Jun 2004 16:24:28 +1000, Bruce Graham
<[email protected]> wrote:

>In article <[email protected]>,
>[email protected] says...
>> Tom Sherman writes:
>>
><snip>
>> > I have driven older cars without power brakes and did
>> > not find the effort excessive: certainly nothing out of
>> > the normal range for fit cyclist.
>>
>> What "older cars" did you drive that had unassisted disc
>> brakes?
>>
>VW beetles from the late 60's early 70's. Porsche 911/912
>from introduction (64) until quite recently (late 80's?)
>
>
>> > Brake boosters (in most cases) change the feel of the
>> > brakes in a manner that makes modulation more
>> > difficult. Power brakes (in a reasonably sized vehicle)
>> > are no more necessary that power steering
>> > is.[1]
>
>Porsche factory said this re the 911 for a long time.
>>
>> I think you are mistaking the poor response of drum
>> brakes for power disc brakes. Todays disc brakes are as
>> linear and controllable as you can expect, far better
>> than brakes without power assist.
>>
>> Drum brakes got by without power assist for a long time
>> because drums use self servo (self activating leading
>> shoes) whose effectiveness varied with temperature and
>> humidity, so much so that they locked up on occasion.
>> The non-linearity of drum brakes is what got rid of
>> them. Discs in contrast are linear (braking proportional
>> to pedal pressure) but because they have a low
>> coefficient of friction that, except for the lightest
>> cars, require a brake booster. These boosters are vacuum
>> driven in most cars.
>>
>Porsche customers said this for even longer - they won!
>

Dear Bruce,

The customer is always right.

It may also be worth pointing out in all this talk about
assisted braking that about half the auto industry's

here on rec.bicycles.tech.

Forget any smaller-than-average men who ride bicycles and
post here. Think of women around 5'4" and 110 pounds.
Several such sources have just told me that power brakes
(and steering) are damned useful.

Sensitively,

Carl Fogel
 
Bruce Graham wrote:

> In article <[email protected]>,
> [email protected] says...
>
>>Tom Sherman writes:
>>
>
> <snip>
>
>>>I have driven older cars without power brakes and did not
>>>find the effort excessive: certainly nothing out of the
>>>normal range for fit cyclist.
>>
>>What "older cars" did you drive that had unassisted
>>disc brakes?
>>
>
> VW beetles from the late 60's early 70's.

Our '75 VW Rabbit (aka Golf) had unassisted front disc
brakes. As does the '87 Chevy Nova that I gave to our
daughter last year. My primary vehicle is now an '89
Cannondale - it also has unassisted disc brakes (the discs
being the rims).

> Porsche 911/912 from introduction (64) until quite
> recently (late 80's?)
 
<[email protected]> wrote in message
news:[email protected]...
> Mark South writes:
>
> >>> Today I experienced something new.
>
> >>> About 20 km into my Sunday morning ride, I was coming
> >>> up a gentle hill into a tiny village and thinking
> >>> "Hell, I must be getting weaker every day, why is this
> >>> incline so hard?"
>
> >> well, after all that, what was it?
>
> > Good question. I still am not certain, but it seems to
> > me that my original explanation based on thermal
> > expansion of the brake pads was the correct one.
>
> Thermal expansion, even in soft material like bicycle
> brake pads cannot take up that clearance unless they were
> dragging after they were last adjusted.

They were not dragging, but they were very close. The rim
is laterally true within less than .5 mm and the pads have
only enough clearance to not drag on the rim when
everything is cool.

> > When the bike is left in my cool garage overnight the
> > brake develops a little more travel and this reduces
> > again when I'm out on the road.
>
> > I run the pads very close to the rim to start with, so
> > it didn't take much to make them bind, I guess.
>
> You must be running with less than 0.5mm total clearance
> for that to go away thermally but then you didn't comment
> on whether the brake was off center (more clearance on one
> side than the other). Dual pivot brakes cannot swivel
> except permanently, by rotating the anchor bolt. That is
> what I think happened. Somewhere along the way the brake
> caliper got pushed to one side.

The brake is and was perfectly centred. When I stopped
and noticed the pads binding, they were both squeezed
onto the rim.

> Check how easily the caliper and bolt can be rotated
> bolt with the wheel removed. It should not be movable by
> hand if the bolt is tight. If this brake is operating
> with less than 0.5mm clearance it is set too closely and
> will drag even if perfectly centered when pedaling
> standing on hills. When the bottom of the wheel is side
> loaded to the right, the top moves to the right also and
> will cause drag.

Perhaps you're right. The brake pads remained dragging on
the rim when I got off the bike though.

As I said, I fixed it by adding some clearance, but I can
still see (and feel through the levers) the variation in
clearance with temperature.

Perhaps I got a batch of pads with an unusually large (tail
of the distribution) thermal expansion ratio?

> Wheel flex of rear wheels in climbing is why Campagnolo
> reverted to a single pivot, lower mechanical advantage
> brake for the rear with more clearance. Such a brake does
> not need to be dual pivot. Clearance is governed by how
> high the mechanical advantage. Car disk brakes, for
> instance, run with practically no clearance and have a
> high mechanical advantage that is still too low without
> power assist. At least their brakes have float to accept
> elastic movement of the wheel and disc.

So you are saying I should fit disk brakes on my road bike?

(Ducks and runs :)
--
Mark South: World Citizen, Net Denizen
 
Tom Sherman writes:

> Having driven 135,000+ miles in cars with 4-wheel disc
> brakes and power assist but no anti-lock, I feel that I am
> quite familiar with that type of system. I have also
> driven plenty of pickups and vans with rear wheel drum
> brakes, so I am all too aware of their poor modulation and
> "self-energizing" effect.

Just because you drive cars doesn't qualify you as
understanding the works of the brakes. I'm sure you can
strike up a conversation with a truck driver at a truck-
stop cafe and get all sorts of testimonials on the benefits
of various equipment, some of which is pure folklore and
other parts that happen to coincide with fact. Mileage does
not an automotive engineer make, so take it easy on the
mileage claims.

>>> [1] I used to drive a 1972 Oldsmobile with a broken
>>> power steering pump. That car had close to 3000
>>> pounds of weight on the front wheels. At the time I
>>> weighed less than 140 pounds and certainly DID NOT
>>> have above average upper body strength.

>> So what are you proposing? How does this affect brakes?

> The point is that power assisted braking and steering (not
> to mention automatic transmissions) are used in cars
> because they are designed for lazy people who expect to
> put out no effort, not out of necessity.

Tell that to Michael Schumacher and his competitors. The
power brake is an essential part of good braking and cars
that don't use it are either light enough to squeak by or
too cheap to use it.

The basic concept of a brake is that it is a force
transducer, not a position transducer as steering is. Good
Brake response is proportional to pedal pressure, not
stroke. In fact the stroke involved is counterproductive
because it changes the leverage of the leg and the feel of
how hard the brake is being applied. Stroke on power
assisted brakes is a necessary evil of having to also work
(with diminished capacity) without assist.

Your "lazy people" reference discredits what you say on this
at the outset.

Jobst Brandt [email protected]
 
[email protected] wrote:

> ... Your "lazy people" reference discredits what you say
> on this at the outset....

It was in reference to a certain rec.bicycles.tech regular
who likes to comment on the inability of people to use items
such as full size frame pumps, ride long distances without
drinking water, and to use lower mechanical advantage
bicycle brakes.

--
Tom Sherman – Quad City Area
 
Tom Sherman writes:

>> Your "lazy people" reference discredits what you say on
>> this at the outset....

> It was in reference to a certain rec.bicycles.tech regular
> who likes to comment on the inability of people to use
> items such as full size frame pumps, ride long distances
> without drinking water, and to use lower mechanical
> advantage bicycle brakes.

Why don't you speak for yourself instead of dodging and
making allusions? There is no doubt that many riders are
not able to pump tires with a 20mm diameter piston frame
pump or stop their bicycles safely with 4:1 ratio hand
brakes. They have said so here on this group and have
ceased to complain about it with the advent of dual pivot
brakes and micro-pumps. What does this have to do with
power brakes and their response?

"Lazy people" is not a parameter here nor is it with
power brakes.

Your "a certain rec.bicycles.tech regular" doesn't say what
your problem with this is. You display inhibitions in
expressing what you mean. Speak up!

Jobst Brandt [email protected]
 
Bruce Graham <[email protected]> writes:

> In article <[email protected]>,
> [email protected] says...
>> Tom Sherman writes:
>>
> <snip>
>> > I have driven older cars without power brakes and did
>> > not find the effort excessive: certainly nothing out of
>> > the normal range for fit cyclist.
>>
>> What "older cars" did you drive that had unassisted disc
>> brakes?
>>
> VW beetles from the late 60's early 70's.

Sorry, drum brakes. At least if my wife's '72 Super Beetle
was anything to go by.
 
[email protected] wrote:
> Tom Sherman writes:
>
>
>>Having driven 135,000+ miles in cars with 4-wheel disc
>>brakes and power assist but no anti-lock, I feel that I am
>>quite familiar with that type of system. I have also
>>driven plenty of pickups and vans with rear wheel drum
>>brakes, so I am all too aware of their poor modulation and
>>"self-energizing" effect.

actually, the two reasons brakes have gone to disk
from drum are:

1. disks cool much quicker so therefore are much more
fade resistant. ask any big rig driver about fade in
drum brakes.

2. if they get wet, drums are hard to dry out - disks dry
almost immediately so disks are much safer.

and it's too simplistic to claim "poor modulation" on a rear
drum brakes
- it takes no account of load compensation or
proportioning devices.

>
>
> Just because you drive cars doesn't qualify you as
> understanding the works of the brakes. I'm sure you can
> strike up a conversation with a truck driver at a truck-
> stop cafe and get all sorts of testimonials on the
> benefits of various equipment, some of which is pure
> folklore and other parts that happen to coincide with
> fact. Mileage does not an automotive engineer make, so
> take it easy on the mileage claims.
>
>
>>>>[1] I used to drive a 1972 Oldsmobile with a broken
>>>> power steering pump. That car had close to 3000
>>>> pounds of weight on the front wheels. At the time I
>>>> weighed less than 140 pounds and certainly DID NOT
>>>> have above average upper body strength.
>
>
>>>So what are you proposing? How does this affect brakes?
>
>
>>The point is that power assisted braking and steering (not
>>to mention automatic transmissions) are used in cars
>>because they are designed for lazy people who expect to
>>put out no effort, not out of necessity.
>
>
> Tell that to Michael Schumacher and his competitors. The
> power brake is an essential part of good braking and cars
> that don't use it are either light enough to squeak by or
> too cheap to use it.
>
> The basic concept of a brake is that it is a force
> transducer,

technically, it's an energy transducer - turns the energy of
motion into heat.

> not a position transducer as steering is. Good Brake
> response is proportional to pedal pressure, not stroke. In
> fact the stroke involved is counterproductive because it
> changes the leverage of the leg and the feel of how hard
> the brake is being applied. Stroke on power assisted
> brakes is a necessary evil of having to also work (with
> diminished capacity) without assist.

air brakes on buses & trucks are sensitive only to stroke,
not force. you can bottom the pedal on an air braked vehicle
no problem. a common mistake make by people learning to
drive an air braked vehicle is to brake much too fiercely
because they're expecting the pedal to stop going down as
they reach some kind of bite point.

>
> Your "lazy people" reference discredits what you say on
> this at the outset.
>
> Jobst Brandt [email protected]
 
jim beam <[email protected]> wrote:
> air brakes on buses & trucks are sensitive only to stroke,
> not force.

Not the ones I drove. Would be a counter-intuitive
concept, btw.

--
MfG/Best regards helmut springer
 
On Sat, 19 Jun 2004 06:06:48 GMT [email protected]
wrote:

>What "older cars" did you drive that had unassisted
>disc brakes?

VW type 3s came with unassisted front disks from '66 to the
end of production in '73. They certainly require more pedal
effort than a car with power brakes, but that's really only
because power brakes require virtually no effort. I've never
had any problem getting one of mine to stop, but I keep the
brakes in good condition. In general, I've always considered
their brakes to be excellent.

People who are used to power brakes are often surprised by
the pedal effort, but I have always assumed that this was
simply because they were used to the zero effort that power
brakes required.

Their rear drum brakes have one leading and one trailing
shoe on each side, but even with the leading shoes, braking
is poor if the fronts aren't working.

Yes, these were light cars; only about 2250 lbs. There are
modern cars, however, that weigh the same and still use
power brakes, but they are generally front engine/drive, and
have virtually all their weight on the front wheels, so
their rear brakes are almost pointless.

-
-----------------------------------------------
Jim Adney [email protected] Madison, WI 53711 USA
-----------------------------------------------
 
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