Drum Brakes and Disc Brakes, A Historical Question

In the early part of the last century, there were a lot of different
styles of brakes. Seems that we all settled on the internal drum brake
for a good part of the century.

Drum brakes worked. They stopped the car.


Thing is, we all know these days that disc brakes are superior. Better
stopping power, better cooling ability, self-adjusting for wear, etc.
The thing that I can't seem to wrap my noodle around though, is why
didn't we see them sooner? Compared to drum brakes, disc brakes are a
much simpler design. I would wager that it is even cheaper to make
disc brake sets. The master cylinder is irrelevant- same concepts
apply, just different front/rear proportioning.

I realize that in manufacturing, *nothing* gets changed unless there is
a damn good reason to. But why did it take until when.... Late 1960s,
early 1970s or so until FRONT disc brakes became the norm? How come it
took until now for them to start showing up on the rear wheels?

Was there some enabling technology or manufacturing process that needed
to be developed or invented that made disc brakes possible? I can't
seem to think of anything disc brakes require that drum brakes didn't
already have. Why didn't disc brakes become the norm instead of drum?

Or is this another thing where the rest of the world had 4-wheel disc
brakes since the 1950s, but Detroit refused to 'progress'?

discuss!

phaeton wrote:
> In the early part of the last century, there were a lot of different
> styles of brakes. Seems that we all settled on the internal drum brake
> for a good part of the century.
>
> Drum brakes worked. They stopped the car.
>
>
> Thing is, we all know these days that disc brakes are superior. Better
> stopping power, better cooling ability, self-adjusting for wear, etc.
> The thing that I can't seem to wrap my noodle around though, is why
> didn't we see them sooner? Compared to drum brakes, disc brakes are a
> much simpler design. I would wager that it is even cheaper to make
> disc brake sets. The master cylinder is irrelevant- same concepts
> apply, just different front/rear proportioning.

In many applications discs are not superior to drums. A drum brake has
much more stopping ability than a disc, look at the amount of surface
area covered by a pad versus a set of shoes. Plus drums can be self
assisting as well. Discs are MUCH easier to damage as well.

The real reasons for disc brakes are cost and vehicle weight. a lighter
rotating assembly takes less power to turn, less power means less fuel
burned. They are also less expensive to manufacture and for the company
to install. You don't need any skill to put on a set of discs and pads,
you do need to adjust a set of drums correctly, on the assembly line
that is time they no longer need to pay for. You also make it easier for
the dealer to service the vehicle because anybody can do a brake swap
with discs.

>
> I realize that in manufacturing, *nothing* gets changed unless there is
> a damn good reason to. But why did it take until when.... Late 1960s,
> early 1970s or so until FRONT disc brakes became the norm? How come it
> took until now for them to start showing up on the rear wheels?

It is mainly because they had brakes that worked just fine, until they
started using the 4 wheel anti lock, much easier to modulate a caliper
than a wheel cylinder. Mainly because of the self energizing effects of
the drums.

>
> Was there some enabling technology or manufacturing process that needed
> to be developed or invented that made disc brakes possible? I can't
> seem to think of anything disc brakes require that drum brakes didn't
> already have. Why didn't disc brakes become the norm instead of drum?
>
> Or is this another thing where the rest of the world had 4-wheel disc
> brakes since the 1950s, but Detroit refused to 'progress'?
>
> discuss!
>

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Disc brakes in the form familiar today didn't really start appearing on
the street until the mid-late 50s, AFAIK (after a couple of postwar
false starts).

Although there were a few street four-wheel applications from the
earliest days, that was restricted to uncompromising performance cars
for a long, long time. Four-wheel discs on more of a mass-market car
at something resembling a popular price is 1980s-and-onward stuff, I
think.

Unless you really drive hard, rear drums are fine (the front brakes do
most of the work) and a hard-gripping, mechanically actuated parking
brake is easy to implement.

What changed, I don't know, so I guess this bag of gas didn't really
quite answer your question after all. But maybe it'll help a useful
discussion get going...

Cheers,
--Joe

phaeton wrote:
>
>Or is this another thing where the rest of the world had 4-wheel disc
>brakes since the 1950s, but Detroit refused to 'progress'?

Yep, another clear case of Detroit never thought of it first. ;-)

The other fine example of the syndrome is the Chrysler Hemi Six....
Designed and built in Australia to replace the Slant Six and arguably
one of the best mass production sixes of its era ever built anywhere.
Also, at one stage, the most powerful production six on the planet.

You got the Slant Six and we got the Hemi. We also got our first disc
brakes on a locally built car in 1956 (Triumph TR3). )

--
John H

phaeton wrote:
> In the early part of the last century, there were a lot of different
> styles of brakes. Seems that we all settled on the internal drum brake
> for a good part of the century.
>
> Drum brakes worked. They stopped the car.
>
>
> Thing is, we all know these days that disc brakes are superior. Better
> stopping power, better cooling ability, self-adjusting for wear, etc.
> The thing that I can't seem to wrap my noodle around though, is why
> didn't we see them sooner? Compared to drum brakes, disc brakes are a
> much simpler design. I would wager that it is even cheaper to make
> disc brake sets. The master cylinder is irrelevant- same concepts
> apply, just different front/rear proportioning.

Actually, you're *almost* right. Drums actually give you more brake
torque per unit line pressure than discs, especially the self-energizing
servo type (the ones with the anchor pin at the top, where the friction
of one shoe jams the other one harder into the drum.) My '55 Stude has
factory-style drum brakes (I can't say factory as I've traded the
original smooth drums for finned) with no power booster and it does not
require any particular feats of strength to stop, although it probably
weighs over 3000 lbs.

>
> I realize that in manufacturing, *nothing* gets changed unless there is
> a damn good reason to. But why did it take until when.... Late 1960s,
> early 1970s or so until FRONT disc brakes became the norm? How come it
> took until now for them to start showing up on the rear wheels?
>

Because they really weren't needed, and more importantly, sticking with
drum brakes allowed manufacturers to not provide a power booster, which
is pretty much required with disc brakes, unless it's on a very small
car. Today, however, with heavier traffic and better tires available,
mfgrs. seem to think that they need to provicde better brakes rather
than simpler ones. I can't argue with that, except to say that I'd
rather have good drums than discs with undersized rotors that are just
going to warp in a couple thousand miles.

> Was there some enabling technology or manufacturing process that needed
> to be developed or invented that made disc brakes possible? I can't
> seem to think of anything disc brakes require that drum brakes didn't
> already have. Why didn't disc brakes become the norm instead of drum?
>
> Or is this another thing where the rest of the world had 4-wheel disc
> brakes since the 1950s, but Detroit refused to 'progress'?
>

Not really. Chrysler experimented with a weird type of disc brake in
the 50's and Studebaker introduced the modern disc brake to the US on
the Avanti for the '63 model year. I am not sure when they were first
used in Europe but at least '57 (as my mom had a Triumph with discs, and
my dad hated working on them - apparently he hadn't heard of White Post,
if they were even around in the early 70s) and maybe a couple years
earlier. In any case, whatever the holdup was, the drum brake was
pretty much perfected *before* the discs were introduced.

nate


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

phaeton wrote:

> The thing that I can't seem to wrap my noodle around though, is why
> didn't we see [disk brakes] sooner?

We probably did, but couldn't afford to make them.

Disk brakes need hydraulics, drums can use cable or rod. My Dad's 1932
MG has drums (big ones!) and has an 1950's after-market conversion to
improve the front brakes by converting them to hydraulic. Disk brakes
don't work with cables because the travel is smaller and there's no
self-servo action -- so you need a _lot_ of force in a small travel and
pull-wire systems just can't deliver this. Ask any mountain biker -
bikes have recently discovered disks and the cable systems have very
poor and unreliable performance compared to the hydraulics.

Disk brakes need manufacturing techniques that just weren't available
pre-war, having been developed in wartime to manufacture aircraft
hydraulic power systems (not just brakes). Calipers are a large
diameter piston that must be ground to size if it's to work adequately.
The smaller long travel pistons of a drum system can be turned on a
lathe then simply honed with a semi-manual triple stone.

The first real "mass market" (and that was a very small market, but it
was still a production line not a coachbuilder) car with standard disk
brakes was the Jaguar XK150 in 1957 (a successful import into the USA
too). This was the road development of Jaguar's successful use of disk
brakes with the racing C types and D types at Le Mans.

phaeton wrote:
> In the early part of the last century, there were a lot of different
> styles of brakes. Seems that we all settled on the internal drum brake
> for a good part of the century.
>
> Drum brakes worked. They stopped the car.

Yes, but as cars became faster we needed more reliable braking. Ever
had a set of drums fade or get wet? It's scary.

>
>
> Thing is, we all know these days that disc brakes are superior. Better
> stopping power, better cooling ability, self-adjusting for wear, etc.
> The thing that I can't seem to wrap my noodle around though, is why
> didn't we see them sooner? Compared to drum brakes, disc brakes are a
> much simpler design. I would wager that it is even cheaper to make
> disc brake sets. The master cylinder is irrelevant- same concepts
> apply, just different front/rear proportioning.
>
> I realize that in manufacturing, *nothing* gets changed unless there is
> a damn good reason to. But why did it take until when.... Late 1960s,
> early 1970s or so until FRONT disc brakes became the norm? How come it
> took until now for them to start showing up on the rear wheels?

Front brakes do most of the stopping so you got a big improvement in
braking by just switching the front.


>
> Was there some enabling technology or manufacturing process that needed
> to be developed or invented that made disc brakes possible? I can't
> seem to think of anything disc brakes require that drum brakes didn't
> already have. Why didn't disc brakes become the norm instead of drum?

Probably inertial more than any other reason.

>
> Or is this another thing where the rest of the world had 4-wheel disc
> brakes since the 1950s, but Detroit refused to 'progress'?

Not so on the many domestic and import cars I'm familiar with.


>
> discuss!

phaeton wrote:


>
> I realize that in manufacturing, *nothing* gets changed unless there is
> a damn good reason to. But why did it take until when.... Late 1960s,
> early 1970s or so until FRONT disc brakes became the norm? How come it
> took until now for them to start showing up on the rear wheels?

Front disks make a LOT of sense. The front brakes do about 80-90% of the
work of stopping the car, and heat dissipation is essential- that's what
disks do best.

Rear disks make a lot less sense, for a couple of reasons. First off,
the rear brakes are pretty much along for the ride, dissipating only
10-20% of the braking energy. That's well within the limits of what a
well-designed DRUM brake system can do- after all, 18-wheelers STILL use
drum brakes because they have so much more surface area and are capable
(when designed for it) of more total stopping force, even if it can't be
repeated a dozen times in a row as all the car magazines like to do (but
how often do you make more than 2 "panic stops" in a row in real life,
let alone 5? or 10?)

The second reason drums make sense for rear brakes is because of the
emergency brake. By its very nature the emergency/parking brake has to
be a mechanical brake, not a hydraulic brake. Its super-easy to make a
lever system that will spread the shoes on a hydraulic drum brake
system. IOW, its easy to make the same brake system work by two
different application mechanisms. You cant do that with disks, at least
not easily. And what happens with most rear-disk vehicles is that there
is a tiny DRUM brake mechanism in the center section of the disk rotor
which is mechanically activated for the emergency/parking brake
funciton. Its wasted hardware, adds to cost, and adds to complexity. But
because all the car magazines love to hype the "new" (disk brakes and
overhead cams for everyone!) even when the old may function as well or
better, there's a perception advantage to rear disks. People view rear
disk cars as "more advanced" than rear drum cars. Hell, there are even
multi-thousand dollar kits to convert old muscle cars to rear disks- a
COLOSSAL waste of money since converting the fronts to disk is where
100% of improved stopping performance comes from... NOT from converting
the rears. But its sure making money!



>
> Or is this another thing where the rest of the world had 4-wheel disc
> brakes since the 1950s, but Detroit refused to 'progress'?

A patently false statement, no dicsuccion required. Yes, SOME
high-performance european cars had disks in the 50s and 60s. So did some
high-end American cars. But the VAST majority of all cars stuck with
drum brakes through the mid 60s. At that point, American and European
everyday cars moved very quickly to front disks to the point that it was
practically universal within 5-7 years. Rear disks were hit-and miss,
but until the 90s American makers didn't succumb to the false
perceptioin that rear disks were a performance enhancement of the same
magnitude that front disks were.

John S. wrote:


>
>
> Yes, but as cars became faster we needed more reliable braking. Ever
> had a set of drums fade or get wet? It's scary.
>

Its just as scary when disks fade or get wet... and don't pretend it
doesn't happen. Its less *likely* (well, the fade part, wetness is about
equally likely) so disk brake fade is rarely encountered on street cars.
But it happens.

Steve wrote:
> John S. wrote:
>
>
> >
> >
> > Yes, but as cars became faster we needed more reliable braking. Ever
> > had a set of drums fade or get wet? It's scary.
> >
>
> Its just as scary when disks fade or get wet... and don't pretend it
> doesn't happen. Its less *likely* (well, the fade part, wetness is about
> equally likely) so disk brake fade is rarely encountered on street cars.
> But it happens.


Highly unlikely...not impossible, but close to it.