Braking in New Handbrake shoes and Disks

In article >,
Jeff Strickland > wrote:
> > I'm not sure how you could design a friction brake that only worked to
> > hold the car stationary? Although you could mess about with the
> > linings so it had the very best friction under those conditions?. But
> > if all it was required to do was just this, then a mechanical lock -
> > like you have on an auto - would be perfect. But handbrakes are the
> > same as the normal working brakes in principle, ie friction. And do
> > the job rather badly on the average BMW.
> >


> A mechanical lock that used pins into a spline, or equivelent, AND if
> the car was nudged for any reason, then the pins could sheer and the
> brake would be rendered useless.

Make it strong enough and the tyres would simply slide.

> If the parking brake was a pad of any
> sort that pressed against a surface, and the car was nudged, then the
> pad and surface could slip and set to the new position without
> destruction of the system.

If you've designed this magical friction material which is super efficient
at rest, but near useless when moving, the car will simply continue on its
way?

> All a Parking Brake has to do is keep a vehicle that is at rest at rest.
> A parked car needs to remain parked. This is what a parking brake does.

It needs to hold efficiently on *any* hill, and also against the force of
an auto in drive. To do this so the most wimpy person can use it easily
means it would probably be a half decent emergency brake too?

But in any case I disagree it works well as a parking brake.

> Yes, they _could_ have linked it mechanically to the disc brakes and
> called it an emergency brake, but they didn't They created a brake shoe
> and drum that is minimally designed to keep a stationary load
> stationary. I don't understand houw you could possible ask how to design
> a friction brake that only worked to hold a car stationary.

Thought that was your idea?

> BMW Parking Brakes work as good as they need to. They don't make very
> good emergency brakes, but they rise to the challenge of keeping a
> parked car parked, and that is all they need do by definition.

Others make handbrakes that are more efficient. It's not rocket science.

--
*i souport publik edekashun.

Dave Plowman London SW
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"Dave Plowman (News)" > wrote in message
...
> In article >,
> Jeff Strickland > wrote:
>> > I'm not sure how you could design a friction brake that only worked to
>> > hold the car stationary? Although you could mess about with the
>> > linings so it had the very best friction under those conditions?. But
>> > if all it was required to do was just this, then a mechanical lock -
>> > like you have on an auto - would be perfect. But handbrakes are the
>> > same as the normal working brakes in principle, ie friction. And do
>> > the job rather badly on the average BMW.
>> >
>
>
>> A mechanical lock that used pins into a spline, or equivelent, AND if
>> the car was nudged for any reason, then the pins could sheer and the
>> brake would be rendered useless.
>
> Make it strong enough and the tyres would simply slide.
>


Yes, but why screw with it? The Parking Brake does it's job easily and
reliably. And cheaply.




>> If the parking brake was a pad of any
>> sort that pressed against a surface, and the car was nudged, then the
>> pad and surface could slip and set to the new position without
>> destruction of the system.
>
> If you've designed this magical friction material which is super efficient
> at rest, but near useless when moving, the car will simply continue on its
> way?
>

What are you talking about? It's a simple matter of surface area. If the
surface area of the brake is small, it will not change a dynamic load into a
static load very efficiently, but will easily keep a static load from
becoming a dynamic one.

The very fact that this needs to be explained again and again shows that you
just don't get it Dave. I thought you were smarter than this.




>> All a Parking Brake has to do is keep a vehicle that is at rest at rest.
>> A parked car needs to remain parked. This is what a parking brake does.
>
> It needs to hold efficiently on *any* hill, and also against the force of
> an auto in drive. To do this so the most wimpy person can use it easily
> means it would probably be a half decent emergency brake too?
>

There is no need for it to work against the force of the transmission in
Drive. Indeed, Drive at idle is a load that it can easily hold in place, but
there is no reason to think that mashing the gas will be kept in check by
the parking brake. I have never owned a car with a parking brake that could
not be overpowered by an automatic transmission if therer was enough effort
put into the abuse.




> But in any case I disagree it works well as a parking brake.
>
>> Yes, they _could_ have linked it mechanically to the disc brakes and
>> called it an emergency brake, but they didn't They created a brake shoe
>> and drum that is minimally designed to keep a stationary load
>> stationary. I don't understand houw you could possible ask how to design
>> a friction brake that only worked to hold a car stationary.
>
> Thought that was your idea?
>

It was my idea, and you questioned how it could be possible to have such a
design.




>> BMW Parking Brakes work as good as they need to. They don't make very
>> good emergency brakes, but they rise to the challenge of keeping a
>> parked car parked, and that is all they need do by definition.
>
> Others make handbrakes that are more efficient. It's not rocket science.
>

True, it isn't rocket science. Anybody could do it, but the fact remains
they didn't do it for whatever reason. It is beyond the scope of the Parking
Brake system to haul a moving car to a standing stop with any degree of
effenciency. Yes, the car will eventually stop, but that is not the
objective of a Parking Brake. That is the objective of an Emergency Brake,
but not of a Parking Brake.

In article >,
Jeff Strickland > wrote:
> Yes, but why screw with it? The Parking Brake does it's job easily and
> reliably.

Perhaps on your car. But not on mine.

> And cheaply.

You're right there.


> >> If the parking brake was a pad of any
> >> sort that pressed against a surface, and the car was nudged, then the
> >> pad and surface could slip and set to the new position without
> >> destruction of the system.
> >
> > If you've designed this magical friction material which is super
> > efficient at rest, but near useless when moving, the car will simply
> > continue on its way?
> >

> What are you talking about? It's a simple matter of surface area. If the
> surface area of the brake is small, it will not change a dynamic load
> into a static load very efficiently, but will easily keep a static load
> from becoming a dynamic one.

> The very fact that this needs to be explained again and again shows that
> you just don't get it Dave. I thought you were smarter than this.

Err, care to measure the 'surface area' of the rear pads and then that of
the handbrake shoes? ;-)



> >> All a Parking Brake has to do is keep a vehicle that is at rest at
> >> rest. A parked car needs to remain parked. This is what a parking
> >> brake does.
> >
> > It needs to hold efficiently on *any* hill, and also against the force of
> > an auto in drive. To do this so the most wimpy person can use it easily
> > means it would probably be a half decent emergency brake too?
> >

> There is no need for it to work against the force of the transmission in
> Drive. Indeed, Drive at idle is a load that it can easily hold in
> place, but there is no reason to think that mashing the gas will be
> kept in check by the parking brake. I have never owned a car with a
> parking brake that could not be overpowered by an automatic
> transmission if therer was enough effort put into the abuse.

I'm talking about at idle in drive. Facing downwards on a steep hill.

> > But in any case I disagree it works well as a parking brake.

> >> Yes, they _could_ have linked it mechanically to the disc brakes and
> >> called it an emergency brake, but they didn't They created a brake
> >> shoe and drum that is minimally designed to keep a stationary load
> >> stationary. I don't understand houw you could possible ask how to
> >> design a friction brake that only worked to hold a car stationary.

> > Thought that was your idea?


> It was my idea, and you questioned how it could be possible to have such
> a design.


> >> BMW Parking Brakes work as good as they need to. They don't make very
> >> good emergency brakes, but they rise to the challenge of keeping a
> >> parked car parked, and that is all they need do by definition.
> >
> > Others make handbrakes that are more efficient. It's not rocket
> > science.
> >

> True, it isn't rocket science. Anybody could do it, but the fact remains
> they didn't do it for whatever reason. It is beyond the scope of the
> Parking Brake system to haul a moving car to a standing stop with any
> degree of effenciency.

It's beyond the ability of it to just hold the car stationary under some
circumstances. Oh - and not just on my particular car. Many others have
complained about it. It's undoubtedly made worse by the 'creep' with an
auto, and most will simply hold the car on the footbrake. But that's not
the point.

> Yes, the car will eventually stop, but that is
> not the objective of a Parking Brake. That is the objective of an
> Emergency Brake, but not of a Parking Brake.

I don't know why you keep on bringing up an emergency brake, since this
isn't really needed with dual circuit brakes. But an efficient parking
brake would also by nature be one from low speeds.

All that's needed is to increase the mechanical advantage of the system -
ie, increase the maximum available clamping force. But then you'd also
need a self adjusting mechanism.

--
*If you try to fail, and succeed, which have you done?

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" > wrote in message
...
> > What are you talking about? It's a simple matter of surface area. If the
> > surface area of the brake is small, it will not change a dynamic load
> > into a static load very efficiently, but will easily keep a static load
> > from becoming a dynamic one.
>
> > The very fact that this needs to be explained again and again shows that
> > you just don't get it Dave. I thought you were smarter than this.
>
> Err, care to measure the 'surface area' of the rear pads and then that of
> the handbrake shoes? ;-)

More importantly, take a worn shoe out and notice how little of the surface
area has been contacting the drum due to bad alignment. Ccompare *that* to
you disc brake pad surface area -- which operates farther from the axis and
thefore has more leverage anyway.

> It's beyond the ability of it to just hold the car stationary under some
> circumstances. Oh - and not just on my particular car. Many others have
> complained about it. It's undoubtedly made worse by the 'creep' with an
> auto, and most will simply hold the car on the footbrake. But that's not
> the point.

All 3 E30's I've driven had the same problem, parking brake is too weak to
hold the car on a driveway-grade hill. Any of the crappy entry-level
Pontiacs from my youth could lock the rear wheels at 30kph easily with their
foot actuated parking brakes. Not so the bimmers.

> All that's needed is to increase the mechanical advantage of the system -
> ie, increase the maximum available clamping force. But then you'd also
> need a self adjusting mechanism.

Which is absent, hence my comment about shoe alignment.

-Russ.

In article >,
Somebody > wrote:
> All 3 E30's I've driven had the same problem, parking brake is too weak
> to hold the car on a driveway-grade hill. Any of the crappy entry-level
> Pontiacs from my youth could lock the rear wheels at 30kph easily with
> their foot actuated parking brakes. Not so the bimmers.

Yup. I had a '60s Rover P6 3500 with inboard rear discs with the handbrake
operating on these. It was a fairly involved mechanism, with a mechanical
self adjuster for both foot and handbrake in the caliper. The caliper
pivoted, but had only one hydraulic piston. It also would easily lock the
rear wheels at 30 mph with minimal effort on the handbrake. So it can be
done. BMW have simply saved money with a crappy design. A decent drum
handbrake would need to be about 10" and self adjusting as providing the
required amount of leverage would leave no room for wear, etc.

--
*A fool and his money can throw one hell of a party.

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" > wrote in message
...
> In article >,
> Somebody > wrote:
> > All 3 E30's I've driven had the same problem, parking brake is too weak
> > to hold the car on a driveway-grade hill. Any of the crappy entry-level
> > Pontiacs from my youth could lock the rear wheels at 30kph easily with
> > their foot actuated parking brakes. Not so the bimmers.
>
> Yup. I had a '60s Rover P6 3500 with inboard rear discs with the handbrake
> operating on these. It was a fairly involved mechanism, with a mechanical
> self adjuster for both foot and handbrake in the caliper. The caliper
> pivoted, but had only one hydraulic piston. It also would easily lock the
> rear wheels at 30 mph with minimal effort on the handbrake. So it can be
> done. BMW have simply saved money with a crappy design. A decent drum
> handbrake would need to be about 10" and self adjusting as providing the
> required amount of leverage would leave no room for wear, etc.
>

You guys are missing the point, the example you gave of a '60s era Pontiac
used the actual brakes for stopping as a Parking Brake. Frankly, in those
days, the parking brake was reasonably termed an Emergency Brake. It could
be called upon to stop the car if needed. The trouble was that there was a
court case where a person told the judge, "it was an emergency, so I used
that brake to stop sooner." Shortly after that, it became known as a parking
brake.

You have to think of what they - the engineers - have as the goal, not of
what you would like it to do. The ONLY goal is to hold the car in place once
you have found a parking spot. It does this job very well, IF it is adjusted
properly. My bitch about the parking brake is that it is a bitch to adjust
properly.

In article >,
Jeff Strickland > wrote:
> You guys are missing the point, the example you gave of a '60s era
> Pontiac used the actual brakes for stopping as a Parking Brake. Frankly,
> in those days, the parking brake was reasonably termed an Emergency
> Brake. It could be called upon to stop the car if needed. The trouble
> was that there was a court case where a person told the judge, "it was
> an emergency, so I used that brake to stop sooner." Shortly after that,
> it became known as a parking brake.

I'm not missing the point, Jeff, you are. A parking brake should be
capable of holding the car stationary on *any* hill using modest force -
the amount anyone could be expected to provide. The one on my car isn't -
despite being in perfect condition. Neither was the previous one on my
E34. Or in the previous E28.

Its use as an emergency brake became redundant after dual circuit brakes
came in.

With an auto, the problem is not great. But with a manual, doing hill
starts on a steep hill would be a real pain.

--
*When companies ship Styrofoam, what do they pack it in? *

Dave Plowman London SW
To e-mail, change noise into sound.

In article >,
Jeff Strickland > wrote:
> The ONLY goal is to hold the car in place once you have found a parking
> spot.

Err, hill starts on a steep hill in a manual? Or do you just hold it on
the clutch? And do you ever have a full load in your car?

> It does this job very well, IF it is adjusted properly. My bitch
> about the parking brake is that it is a bitch to adjust properly.

Easy enough with the correct technique. But given the quality of the rest
of the mechanics, it should be self adjusting. Self adjusting brakes have
been around for a long, long, time.

It's just cheap and nasty.

--
*Lottery: A tax on people who are bad at math.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
<snip>
>
> With an auto, the problem is not great. But with a manual, doing hill
> starts on a steep hill would be a real pain.
>

While I agree that the parking brakes don't work very well, starting on
hills is really not a problem if you can drive a manual properly. Hill
starts should be done using the service brake with heel-and-toe, not
with the parking brake. Irrespective of the hill's slope, it is not
difficult to start this way without any backward movement and without
excessive clutch wear.

JRE

Dave Plowman (News) wrote:
> In article >,
> Jeff Strickland > wrote:
> > The ONLY goal is to hold the car in place once you have found a
parking
> > spot.
>
> Err, hill starts on a steep hill in a manual? Or do you just hold it
on
> the clutch? And do you ever have a full load in your car?
>


Also a nightmare if you have another car sitting right behind your rear
bumper and the traffic is only inching forward once in a while. Even
worse if you have to back up a steep ramp for some reason (like the
garage door not opening for some reason). Without the handbrake you
will have to slip your clutch a lot more than you'd care to.


> > It does this job very well, IF it is adjusted properly. My bitch
> > about the parking brake is that it is a bitch to adjust properly.
>
> Easy enough with the correct technique. But given the quality of the
rest
> of the mechanics, it should be self adjusting. Self adjusting brakes
have
> been around for a long, long, time.
>
> It's just cheap and nasty.
>


The one in my 540 works just fine and the damn car is even heavier than
yours. Unless the tolerances are really that sloppy there must be
something wrong with yours.



> --
> *Lottery: A tax on people who are bad at math.
>
> Dave Plowman London SW
> To e-mail, change noise into sound.