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!
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phaeton wrote:

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.

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.

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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
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phaeton wrote:

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). :))
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As I recall, here in the U.S. we got our first disc brakes on the 1949 Crosley, which also featured an overhead-cam 4-cylinder engine.
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Roger Blake wrote:

Discontinued due to design problems shortly after its introduction IIRC. :)
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John_H wrote:

Discontinued which? The braking system, the OHC 4-cyl, or the whole car altogether?
:-P
-phaeton
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wrote:

The brakes could not stand up to salted winter roads (salting was a practice just starting at the time). The Crosley discs just corroded and locked up as soon as the salt hit them, so they were quickly discontinued.
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phaeton wrote:

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.

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.

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
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phaeton wrote:

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.
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phaeton 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.

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

Probably inertial more than any other reason.

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

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John S. wrote:

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.
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Steve wrote:

Highly unlikely...not impossible, but close to it.
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John S. wrote:

I've experienced both. The wetness part is very common- so common that I've gotten used to braking way early when I drive my truck in the rain. I've apparently got some glazing too that doesn't help things, but it apparently has just the right aerodynamics underneath it to soak the brakes when driving at highway speeds. It used to be that I'd hit the brakes in the rain and nothing would happen for about half a football field. I've since changed my braking habits and it appears that i've 'worn off' the glazing, if that's possible. Either way, I can stop now.
Brake fade was on hwy 140 in northern Nevada. It was a steep, narrow, mountainous road with about a 200 drop on one side (no guard rail) and loose boulders falling down the other side. Myself and all my worldly possessions were navigating this ever so gingerly when the brakes started to fade about halfway through each sharp little corner. There are few times in my life where I was so scared. I started doing all kinds of desperate things like turning on the AC full blast, dropping all the windows and turning on ever electrical accessory I had to try and increase 'drag' on the engine.
I eventually came across a fairly flat stretch of road that was about 400 feet long. I shut the engine off (kept it in gear) and stood on the brake pedal to come to a stop. And sat there for awhile, hoping nobody would come around either corner and annhiliate me. I probably could have lit a cigarette off the rotors. It was broad daylight and I swear they were glowing.
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phaeton wrote:

To be sure, it is possible to fade discs as well, you just have to work at it and ride 'em a lot more. That's why I use gears as well as brakes to control speed in the mountains. It's easy for that speed to creep up and hauling that 4,000 pound car down takes a lot more braking effort than holding a constant speed. The guys I've seen that get themselves into trouble go fast into a corner, hit the brakes and repeat the process in the next corner. No set of brakes is designed to take that kind of purposeful mistreatment for an extended time.
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Porsche's brakes are. Other manufacturers are not quite as competent (even the ones who are willing to spend the same kind of money and use the same suppliers (Brembo calipers, I think, although Porsche says that they make the cross-drilled disks (which are not made by drilling) in-house).
And, BTW, "purposeful mistreatment" ?
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John S. wrote:

You don't do much mountain driving, do you?
And the wet part happens equally with drums or disks. Disks just dry out a little quicker.
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phaeton wrote:

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!

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.
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Yes, although I think your numbers are a bit high. From what I have read 80% / 20% is a brake distribuition usual for FWD cars which usually have a static weight distribution around 67/33. RWD cars try to have distributions of about 50/50, so brake distribuition should be less biased to the front.
But brake distribution is not the whole story. Me and a friend used to have 2 similar cars (Honda Concerto vs Rover 214, made in the same factory AFAIK). The Honda's brakes were good while the Rover's where quite bad. And one of the big differences was the pedal travel: the Rover, with rear drums, had a much softer and long-travel pedal.
I am not saying that the rear disks versus drums was the only difference, (it is likely that the Honda's front disks were also bigger (I think they were ventilated)) but my current car with 4 disks also has a much better feel in the brake pedal, so I think it was a large factor.

In a mountain road, you might not be doing any "panic stops", but the brake effort can be similar or bigger. I remember a magazine article in which they descended a mountain and managed to overheat most of the car's brakes (I think the test was intended to be a bit of a worst test case, so the drivers were not trying to save the brakes).
Also, in the current environment, a sporty car should be able to endure a lap of two of a circuit (track days are getting increasingly popular in several countries). Some cars (BMWs M3, M5, etc., for instance) can overheat in just one lap.

Brake disks that can be actuated by a cable existed 30 years ago already. (I don't remember the name. Girling ?) That system used a moving caliper and so it is not as high-performance as a 4 piston brake caliper, but it is enough for rear wheels.
I think my current car uses such a system, since it doesn't seem to have drums.

Probably not. Some European brands might have transitioned first. I am thinking of Volvo (because of their focus on safety) and Jaguar (because they were the first to win at Le Mans with disk brakes). I don't remember what Mercedes and BMW used to use, but I think many models had rear drums.
Cheaper brands like Opel, VW, Peugeot, Renault, Fiat had rear drums in most models. Citroen (in the 70s) was a bit of an exception. IIRC, the GS has 4 disk brakes.
BTW, a summary history of brakes (from an American point of view):
http://www.brakesguide.com /
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everyone wrote:

Excellent! I'm starting to really dig this ng. I like discussing things like this with informed people.
Braking force/brake booster- This here might be the very thing I overlooked. Now that you all mention this, it *did* occur to me at some point in the past why you can drive an old heavy-as-a-whale car without power steering or power brakes. But Gawds help you if you try to drive some modern car without power assistance, or with broken power assistance. Braking force on discs vs drums (with servo action), SLA/steering box front suspension versus strut/rack-n-pinion? I realize that this is why the steering wheel in a 53 Bel Air is as big around as a hula hoop, but once again.... surely there's a reason why they didn't arrive at rack and pinion steering first... (maybe we'll cover that one later)
Braking area- Do drums *always* have more area? I thought that the forward-facing shoe actually turns (mostly) away from the drum (once again, servo action), pivoting on the wheel cylinder 'rod', in order to force the rear facing shoe into the drum. Thus, you have 100% contact on the rear shoe (which is shaped ever so differently), but only about 10% on the front. If I'm wrong please correct me. I understand that my perception of comparative area might also be skewed because a great deal of disc brakes that I've seen have actually been on race cars- unsurprisingly the rotors were huge and so were the calipers.
Steve wrote:

This is actually going to be the subject of my next little 'tirade'. But I was going to wait till this topic had run its course, first. If I post 15 half-informed topics at once, y'all might think I'm trolling ;-)
Thanks for the discussion!
-phaeton
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