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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / November 2006Drum 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! > 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 [quoted text clipped - 9 lines] > 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 [quoted text clipped - 5 lines] > > discuss! 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 >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). :))  SignatureJohn H > 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). :)) 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. SignatureRoger Blake (Subtract 10 for email.) >> 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). :)) > >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. Discontinued due to design problems shortly after its introduction IIRC. :) SignatureJohn H > >> 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). :)) [quoted text clipped - 7 lines] > -- > John H Discontinued which? The braking system, the OHC 4-cyl, or the whole car altogether? :-P -phaeton > Discontinued which? The braking system, the OHC 4-cyl, or the whole > car altogether? 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. SignatureRoger Blake (Subtract 10 for email.) > 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 [quoted text clipped - 9 lines] > 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 [quoted text clipped - 3 lines] > 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 Signaturereplace "fly" with "com" to reply. http://home.comcast.net/~njnagel > 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. > 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. [quoted text clipped - 8 lines] > 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! > 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. > > Yes, but as cars became faster we needed more reliable braking. Ever > > had a set of drums fade or get wet? It's scary. [quoted text clipped - 3 lines] > equally likely) so disk brake fade is rarely encountered on street cars. > But it happens. Highly unlikely...not impossible, but close to it. > > > Yes, but as cars became faster we needed more reliable braking. Ever > > > had a set of drums fade or get wet? It's scary. [quoted text clipped - 5 lines] > > Highly unlikely...not impossible, but close to it. 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. > > > > Yes, but as cars became faster we needed more reliable braking. Ever > > > > had a set of drums fade or get wet? It's scary. [quoted text clipped - 32 lines] > could have lit a cigarette off the rotors. It was broad daylight and I > swear they were glowing. 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. > 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. 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" ? Signaturehttp://www.mat.uc.pt/~rps/ .pt is Portugal| `Whom the gods love die young'-Menander (342-292 BC) Europe | Villeneuve 50-82, Toivonen 56-86, Senna 60-94 >>>Yes, but as cars became faster we needed more reliable braking. Ever >>>had a set of drums fade or get wet? It's scary. [quoted text clipped - 5 lines] > > Highly unlikely...not impossible, but close to it. 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. > 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. > > 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. 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. > That's well within the limits of what a > well-designed DRUM brake system can do- after all, 18-wheelers STILL use [quoted text clipped - 3 lines] > how often do you make more than 2 "panic stops" in a row in real life, > let alone 5? or 10?) 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. > The second reason drums make sense for rear brakes is because of the > emergency brake. 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. > > Or is this another thing where the rest of the world had 4-wheel disc > > brakes since the 1950s, but Detroit refused to 'progress'? 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/ Signaturehttp://www.mat.uc.pt/~rps/ .pt is Portugal| `Whom the gods love die young'-Menander (342-292 BC) Europe | Villeneuve 50-82, Toivonen 56-86, Senna 60-94 everyone wrote: >discuss! 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: > Overhead cams 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 > everyone wrote: > >discuss! [quoted text clipped - 8 lines] > to drive some modern car without power assistance, or with broken power > assistance. Gawd(s) help you if you try to stop that 1957 Buick Roadmaster after driving through a deep puddle. > Braking force on discs vs drums (with servo action), SLA/steering box > front suspension versus strut/rack-n-pinion? Was there a question or a confused statement? > I realize that this is > why the steering wheel in a 53 Bel Air is as big around as a hula hoop Wait a minute...the steering wheel is big because of differences in braking forces? Huh??? Steering wheels are usually big because the car is heavy and weighs down on large tires. > 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) Who is the they that should have arrived at rack and pinion steering and when should they have done it. > Braking area- Do drums *always* have more area? More area than what. The surface area of a disc is pretty generous if you think about it. But comparing braking or contact area is pointless - drum and disc systems are two fundamentally different designs. One uses a larger braking surface but lower pressure while the other uses a smaller contact surface and higher pressures to accomplish the same end. > I thought that the > forward-facing shoe actually turns (mostly) away from the drum (once [quoted text clipped - 3 lines] > 10% on the front. If I'm wrong please correct me. > I understand that my perception of comparative area might also be Just what exactly is comparative (braking) area anyway. Never heard of that term. > 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. Sure...extreme speed changes on cars with fat high adhesion tires requires a lot of force to be exerted on the wheels. > Steve wrote: > > Overhead cams [quoted text clipped - 7 lines] > > -phaeton > > Braking force on discs vs drums (with servo action), SLA/steering box > > front suspension versus strut/rack-n-pinion? > > Was there a question or a confused statement? In this context, a poorly worded statement, sorry. Feel free to disregard it. > > I realize that this is > > why the steering wheel in a 53 Bel Air is as big around as a hula hoop > > Wait a minute...the steering wheel is big because of differences in > braking forces? Huh??? Steering wheels are usually big because the > car is heavy and weighs down on large tires. This is also related to the previous citation. It's not apparent, but I was comparing non-power-assisted older cars with newer power-assisted cars. However, my whole spiel into steering is admittedly disjointed and makes little sense, so once again, feel free to disregard this statement. ;-) > > 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) > > Who is the they that should have arrived at rack and pinion steering > and when should they have done it. "They" being auto manufacturers, and 'when' being before the (formerly) traditional steering box-based front suspension/steering systems became the norm. Once again, this is a poorly worded question and statement on my part, and it's actually probably its own topic. I will elaborate if you want me to though. > Just what exactly is comparative (braking) area anyway. Never heard of > that term. In this context, i was meaning "drum brake contact area compared to disc brake contact area". Sorry. > > -phaeton > This is also related to the previous citation. It's not apparent, but > I was comparing non-power-assisted older cars with newer power-assisted > cars. However, my whole spiel into steering is admittedly disjointed > and makes little sense, so once again, feel free to disregard this > statement. ;-) Any comparison of a non-assisted braking system to an ASSISTED braking system with the booster non-functional or disabled is specious. It is FAR harder to stop a car with a dead power brake booster than it is to stop the same car with MANUAL brakes. As an example- my daily driver is a 1966 Dodge Polara. It originally had power drum brakes that would throw you through the windshield with a feather touch on the pedal. It was fine once you were used to it, but a real shocker if you'd been used to driving another car. It was also a single-cylinder master cylinder, which I consider unacceptable to drive daily- a single blown hose would take out the whole system. When I gave the car a makeover last year, part of the upgrade was to put on front disk brakes (bolt-on using a '73 New Yorker as a donor car for the spindles, calipers, rotors, and brake lines). At the same time, I got rid of the whole power assist assembly and replaced it with a manual brake pedal linkage from a '65 Dodge 880, hooked to a modern aluminum master cylinder from an 89 Diplomat, with the proportioning valve, safety valve from the Diplomat. So the car now has a fully split braking system, with safety valve to isolate the halves of the system from each other in the event of a blown hose or wheel cylinder, and warning light that comes on when the safety valve has to do its thing. AND it has manual front disk/rear drum brakes. I *love* the brake feel- its more tactile than power boosted brakes and does have a somewhat higher pedal effort, but much lower pedal effort than just disconnecting a power booster. I can bring that big C-body to a stop faster than the ABS and 4-wheel power disks on my wife's 93 Vision TSi can stop that car. About the only gripe I have is that manual brakes demand that the resting height of the brake pedal be a bit higher than power brakes, because there has to be more total pedal travel. Its back to the feel of my '68 Ford and '49 Plymouth from years gone by- you have to slightly LIFT your foot to move it to the brake pedal, rather than just slide it left. No problem once you're used to it, but I am considering putting power brakes back in (using a modern booster) for just that reason. After all, my wife does like to drive that car, too. She doesn't mind the pedal feel at all, but the height does bug her because she had literally never driven a manual-brake car before in her whole life. I learned on manual brakes, so its second nature to me. > everyone wrote: > [quoted text clipped - 25 lines] > been on race cars- unsurprisingly the rotors were huge and so were the > calipers. "Total Contact" drum brakes (trade name of either Bendix or Lockheed, I forget who came up with it) are just that. The way both the front and rear shoes pivot allow for both shoes to be in total contact with the drum. Earlier brakes (such as the ones on my '49 Plymouth) had separate wheel cylinders for each shoe, and had more contact at the end that the cylinder activated versus the "heel" end of the shoe. The other problem with this type as opposed to the Total Contact design is that the brake is far less effective when the car is going backwards than forward. Backing up really briskly and slamming on the brakes was always "interesting" in my ol '49. > Steve wrote: > >>Overhead cams > > This is actually going to be the subject of my next little 'tirade'. I have no preference as to how the valves get actuated, and I own both types. OHC has advantages.... if you want to turn the engine over 7000 RPM it has BIG advantages. What chafes me is when magazine writers even CARE how the valves work so long as they work. The abuse the old Jeep 4.0L inline 6 got from magazine writers was unforgivable. It was superior in every way compared to most of the Japanese engines they compared it to, but they always ragged on it because it was an "antiquated pushrod engine," despite the fact that it typically returned better acceleration, better mileage, and had more bottom-end torque for offroad rock-crawling than the competition OR its replacement- the OHC 3.7L v6. > everyone wrote: > >discuss! [quoted text clipped - 13 lines] > 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) Not so much the design of the steering mechanism or the difference between SLA and struts - a good recirculating ball steering box is just as good as a good rack and pinion setup, from the driver's perspective; likewise a SLA suspension arguably provides better wheel control than a strut type suspension. Heck, BMW kept using their excellent recirc ball boxes long after everyone else went to R&P and BMW's are renowned for their incredible steering feel and precision. However, back in the day, power steering was always an extra cost option, and cars were designed as such. What this meant was a) the suspension was set up with less caster, to reduce steering effort, and b) the steering *ratio* - i.e. how many degrees the front wheels turned for a given rotation of the steering wheel - was generally set up to provide the driver with more leverage. The first thing that people notice when driving a 50's vintage car is that the steering tends to be a little "numb" (due to the lack of caster) and "slow" (due to the slow ratio) which is just the nature of the beast. And, yes, the steering wheels tended to be large - 17" or even larger, to also give the driver more leverage in slow speed situations. As automakers realized that more and more people were ordering cars with power steering anyway, caster specs were changed and ratios quickened to provide a better experience for the driver, but that made vehicles without power steering almost undriveable unless you had decent upper body strength, so eventually the manual steering option was pretty much dropped across the board except for small, light cars that didn't really need it to begin with. > Braking area- Do drums *always* have more area? I thought that the > forward-facing shoe actually turns (mostly) away from the drum (once [quoted text clipped - 6 lines] > been on race cars- unsurprisingly the rotors were huge and so were the > calipers. Based on looking at the wear patterns on the shoes of drum brakes; I would say that it doesn't appear that the front shoe has appreciably less contact area than the rear as a percentage of total lining area, assuming that the brakes are kept in proper adjustment. That said, from a pure physics standpoint, it really doesn't matter how much lining area there is at all; the greater area is only useful when it comes to resisting fade (as is the ability of the drum or rotor to quickly shed heat buildup.) What is important in terms of brake torque, for either system, is the *diameter* of the drum or disc, as the same frictional force will provide a greater torque on a larger diameter drum or disc. nate > 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? I think it may have had more to do with design and tooling commitments. Retooling for a totally new system takes time and money. When discs were an option, they were more expensive than drums. Back in the day, if you bought a new car on a budget, you went with the cheaper drums. I know the AMC Marlin was available with discs in 1967, so you can bet they'd been working on discs at least a couple of years prior. > Or is this another thing where the rest of the world had 4-wheel disc > brakes since the 1950s, but Detroit refused to 'progress'? Front drums were used by all world manufacturers well into the mid'70s, along with single-circuit master cylinders where local laws permitted. The Japanese, for instance, did not ship us their front drums primarily because they were concerned with up-contenting their vehicles to distinguish them on the American market. This was the same thinking that led them to install reclining seats, radios and resistance-type rear window defoggers as standard at a time when those were options or unavailable at all on North American cars. SignatureTeGGeR® > I know the AMC Marlin was available with discs in 1967, so you can bet > they'd been working on discs at least a couple of years prior. The Rambler Marlin came standard with front power disc brakes for the 1965 model year, these were made optional in '66. (Classic and Ambassador models offered discs as an option starting in '65.) This was a four-piston, fixed-caliper Bendix system with solid rotors. A bizarre "non-servo" drum brake setup was used in the rear. (Was supposed to match the discs without use of a proportioning valve. Virtually impossible to get parts for today!) As I recall, Studebaker offered disc brakes as an option starting in '62 or '63. > Front drums were used by all world manufacturers well into the mid'70s, > along with single-circuit master cylinders where local laws permitted. Rambler made dual-circuit master cylinders standard on all their models (except Metropolitan, which was on its way out) starting in the 1962 model year. I think Studebaker also did so around this time, and Cadillac as well. > The Japanese, for instance, did not ship us their front drums primarily > because they were concerned with up-contenting their vehicles to Some Japanese vehicles shipped to the U.S. did indeed come with drum brakes. This was the case with the Subaru 360 and Star/1100 (the latter had inboard front drums), the early Toyota Coronas, as well as early Datsun pickups. SignatureRoger Blake (Subtract 10 for email.) > > I know the AMC Marlin was available with discs in 1967, so you can bet > > they'd been working on discs at least a couple of years prior. [quoted text clipped - 6 lines] > without use of a proportioning valve. Virtually impossible to get parts > for today!) Studebaker did the same thing; the rear brakes used were actually based on an old pickup truck brake design. I personally like this arrangement; the lack of a prop valve is just one less item to fail. Studebaker however used dual piston calipers, not the later 4-piston type. I'm guessing that the 4-pots hadn't been introduced yet, but I'm willing to be corrected. Is it possible that the Marlin's rear drums shared parts/design with the Avanti? If so, I might be able to help track down parts sources, if this is of personal concern to you. > As I recall, Studebaker offered disc brakes as an option starting in > '62 or '63. late '62, for the '63 model year. Parts were shared with contemporary Jag E-Type. Avantis and "Super" package cars got discs as standard, but since the spindles etc. were shared across all model lines you could order any Studebaker you wanted with disc brakes. > > Front drums were used by all world manufacturers well into the mid'70s, > > along with single-circuit master cylinders where local laws permitted. > > Rambler made dual-circuit master cylinders standard on all their models > (except Metropolitan, which was on its way out) starting in the 1962 model > year. I think Studebaker also did so around this time, and Cadillac as well. Studebaker introduced them for the '63 model year. Not sure about Cadillac. Oddly enough, Studebaker did *not* use the dual circuit master cylinder on cars equipped with disc brakes; I can understand this on the Hawk series which still used the underfloor master cylinder (dating back to prewar cars) and therefore didn't have a dual circuit master cylinder option at all, but on the Larks and Avantis which used the more modern suspended pedal setup I'm not sure what the reasoning behind this decision was. At some point a dual circuit master cylinder was mandated by a FMVSS, I think about 1967? > > The Japanese, for instance, did not ship us their front drums primarily > > because they were concerned with up-contenting their vehicles to > > Some Japanese vehicles shipped to the U.S. did indeed come with drum brakes. > This was the case with the Subaru 360 and Star/1100 (the latter had inboard > front drums), the early Toyota Coronas, as well as early Datsun pickups. So did very early VW Rabbits, for that matter. nate > Studebaker did the same thing; the rear brakes used were actually based > on an old pickup truck brake design. I personally like this > arrangement; the lack of a prop valve is just one less item to fail. Good point. The real problem with the Bendix non-servo drums used in conjuction with the early Rambler disc brakes is lack of parts. At this point most parts catalogs don't even list them properly, unless you can get to the old printed books. Even so the parts have all been discontinued, can't even get replacement shoes any more let alone the bizarre ratcheting adjuster, etc. (At least shoes can be relined.) > willing to be corrected. Is it possible that the Marlin's rear drums > shared parts/design with the Avanti? If so, I might be able to help > track down parts sources, if this is of personal concern to you. It seems to me that at some point I looked into this and found that they were no interchangeable parts. The standard "fix" at this point for those old Rambler disc systems is to retrofit the brakes from a "modern" 1980s-vintage AMC car (like a Concord). Parts for those are still readily available, probably because they were shared with the Jeep line. > behind this decision was. At some point a dual circuit master cylinder > was mandated by a FMVSS, I think about 1967? Yes, as I recall 1967 was the first year for federally-mandated dual circuit brakes. SignatureRoger Blake (Subtract 10 for email.) > In article <1159364617.964034.45080@k70g2000cwa.googlegroups.com>, N8N > wrote: [quoted text clipped - 4 lines] > Yes, as I recall 1967 was the first year for federally-mandated dual > circuit brakes. I thought it was Jan 1, 1968. A bunch of new safety regs came in for the 1968 model year. Headrests, 3-point seat belts, side marker lights, door beams, among other things. AFAIK, 1968 models built in 1967 didn't need them, but some makers installed them early anyway. SignatureTeGGeR® > I thought it was Jan 1, 1968. I thought it was 1967, but I could be wrong, it was a long time ago and I'm going by my own memory. As I recall that same year the collapsible steering columns came into play, though Ford went with a big cushion in the center of the steering wheel at first. (AMC and Checker purchased the GM collapsible columns.) SignatureRoger Blake (Subtract 10 for email.) >> I thought it was Jan 1, 1968. > [quoted text clipped - 4 lines] > and Checker purchased the GM collapsible columns.) > Safety regulations came in dribs and drabs at first. The first may have been headlight height restrictions, and the requirement of sealed beams in 1940. I'm not sure when safety glass was first required. Lap belts were first required in 1965. The 1968 model year saw a whole whack of regulations all at once, sparked by the furor surrounding Ralph Nader's book from a few years earlier. SignatureTeGGeR® > > Studebaker did the same thing; the rear brakes used were actually based > > on an old pickup truck brake design. I personally like this [quoted text clipped - 7 lines] > any more let alone the bizarre ratcheting adjuster, etc. (At > least shoes can be relined.) If it has a ratcheting adjuster, the brakes are NOT the same as a Studebaker. The Studes with front discs used eccentric adjusters behind the shoes. I thought I might be able to help you out, but I guess not. nate >>I know the AMC Marlin was available with discs in 1967, so you can bet >>they'd been working on discs at least a couple of years prior. [quoted text clipped - 9 lines] > As I recall, Studebaker offered disc brakes as an option starting in > '62 or '63. Imperial had a 4-wheel disk system ( with an odd full-disk caliper) briefly in the 50s. I'm not sure exactly when they started, but I know that in 1966 Budd 4-piston disk brakes were optional on all the full-size Chrysler products (Polara, Monaco, Fury, Newport, 300, New Yorker, Imperial). The midsizes (Belvedere/Satellite, Coronet, Charger) had them optionally no later than '67. Both of those systems are now very hard to get parts for- I considered tring to scare up an original Budd system for my Polara but gave up quickly. Most owners of those cars now retrofit the single-piston Kelsey-Hayes calipers that were standard (and darn near universal) in the 70s and 80s. Cheap, available, work 99% as well as 4-piston brakes anyway. The only real advantage of the 4-piston setup is more even inboard vs. outboard pad wear and more tolerance to warped rotors (not necessarily a good thing- I'd rather feel a warped rotor and FIX it, personally). >>>I know the AMC Marlin was available with discs in 1967, so you can >>>bet they'd been working on discs at least a couple of years prior. [quoted text clipped - 12 lines] > Imperial had a 4-wheel disk system ( with an odd full-disk caliper) > briefly in the 50s. Those were the Lambert discs. Not at all like Jaguar's system of 1957. Very odd, and a very interesting concept. The big problem with the Lamberts was that they used the same hydraulic wheel cylinders used by drum brakes, but operated them at 4 times the usual hydraulic pressure. Apparently fluid ruptures were too common for comfort, so the Lamberts were discontinued. SignatureTeGGeR® > Imperial had a 4-wheel disk system ( with an odd full-disk caliper) > briefly in the 50s. I'm not sure exactly when they started, but I know That's right, I had forgotten about that. I never really did 'grok' how that system worked. As far as I know the earliest post-war use of disc brakes in the U.S. was in the 1949 Crosley -- however those were basically unmodified aircraft brakes. These would lock up solid due to corrosion when used on salted winter roads. > Budd system for my Polara but gave up quickly. Most owners of those cars > now retrofit the single-piston Kelsey-Hayes calipers that were standard > (and darn near universal) in the 70s and 80s. Cheap, available, work 99% That's also SOP for the early AMC/Rambler disc brake systems. Retrofitting the single-piston Bendix calipers from 1980s-vintage AMC cars is pretty much a bolt-in operation. SignatureRoger Blake (Subtract 10 for email.) >> I know the AMC Marlin was available with discs in 1967, so you can >> bet they'd been working on discs at least a couple of years prior. [quoted text clipped - 3 lines] > Ambassador models offered discs as an option starting in '65.) This > was a four-piston, fixed-caliper Bendix system with solid rotors. Didn't pretty much every NA manufacturer move to single-piston floating calipers by 1968? > As I recall, Studebaker offered disc brakes as an option starting in > '62 or '63. Well there you go. Far from being behind the curve, it now appears American manufacturers had been working on discs pretty much as long as the Europeans had. >> Front drums were used by all world manufacturers well into the >> mid'70s, along with single-circuit master cylinders where local laws >> permitted. > > Rambler made dual-circuit master cylinders standard on all their > models (except Metropolitan, which was on its way out) ...and wasn't even made by AMC, but by the British Motor Corporation of England on BMC's A30 chassis. It was sold as the Austin Metropolitan in the UK. <snip> >> The Japanese, for instance, did not ship us their front drums >> primarily because they were concerned with up-contenting their [quoted text clipped - 4 lines] > latter had inboard front drums), the early Toyota Coronas, as well as > early Datsun pickups. So there were some exceptions to the rule. The Toyota Corolla was available with front drums as late as 1975, but those were not installed in Canada or the US. SignatureTeGGeR® > Didn't pretty much every NA manufacturer move to single-piston floating > calipers by 1968? I think AMC used the 4-piston Bendix jobs through 1970, moving to Kelsey-Hayes single-piston floating calipers in 1971, and Bendix single-piston in 1975. (Though my '75 Hornet was built early in the model year and still has the KH brakes.) > ...and wasn't even made by AMC, but by the British Motor Corporation of > England on BMC's A30 chassis. It was sold as the Austin Metropolitan in > the UK. The Metropolitan was designed by Nash in the U.S. (actually an outside designer named Bill Flajole). It was determined early on in the Met's design that it would be built overseas to take advantage of lower labor costs and to get around steel shortages in the U.S., Fiat was initially considered, Austin ultimately chosen. There was a book called "The Metropolitan Story" that came out a few years back that goes into the car's history in great detail, and of course much may be found on "thuh web," such as: http://home.insightbb.com/~hoosiermets/page11.html SignatureRoger Blake (Subtract 10 for email.) Speaking of Metros.. A friend of mine in HS had about 5 of those. His last name was "Hudson", and he claimed it was one and the same with the Hudson Automobile company that got absorbed into Chrysler. Says his dad was part of the Hudson RnD team and stayed on in Chrysler up into the 70s. I always thought they were neat little cars, but I don't remember if any of them ran or drove. They were all in a field behind his house, along with some other stuff I have never seen before or since- most notably a set of fuel injection heads for a 440, and a '56 New Yorker with a 392 Hemi prototype in it, a pushbutton transmission, power everything (windows, seats, steering wheel adj, mirror adj, etc) and (of all things) a phonograph that could play 45s. Btw, this has been an interesting thread to read, with all the historical bits. Thanks to everyone who has chimed in! -phaeton >> ...and wasn't even made by AMC, but by the British Motor Corporation >> of England on BMC's A30 chassis. It was sold as the Austin [quoted text clipped - 10 lines] > > http://home.insightbb.com/~hoosiermets/page11.html I had a look at that page. And this one: http://en.wikipedia.org/wiki/Nash_Metropolitan They say nothing about what Nash ended up using as the basis for the Metropolitan. The Wiki page does say the car was built using "existing mechanical components". The Met was built using the Austin A30 chassis and (originally, apparently) the Austin A-series engine. I suspect Bill Flajole ended up contributing little outside of the body styling. The identical chassis and engine family was used for the original Austin-Healey Sprite, although the original Sprite never received a B-series engine. SignatureTeGGeR® > They say nothing about what Nash ended up using as the basis for the > Metropolitan. The Wiki page does say the car was built using "existing You might want to look up the book "The Metropolitan Story" if you are really interested, as it goes into minute detail about how the car was developed. The front suspension was unique to the Met and was Nash-style with the springs high up on the upper control arms. I don't know if the floorpan (it's a unibody car, so no "chassis" in the sense of a separate frame) is shared with any Austin models of the day. The initial prototypes were made using Fiat running gear. Engine and drivetrain of production models were 100% Austin, though interestingly the 4-speed gearbox was converted to 3-speed by locking out first gear. (Nash did extensive consumer research and drivers at that time were accustomed to 3-speed tranny with column shift.) SignatureRoger Blake (Subtract 10 for email.) >> They say nothing about what Nash ended up using as the basis for the >> Metropolitan. The Wiki page does say the car was built using [quoted text clipped - 13 lines] > out first gear. (Nash did extensive consumer research and drivers at > that time were accustomed to 3-speed tranny with column shift.) Your implication is that the unibody may be unique to the Met. I'm sure you're right, but... Taking your advice, I did some Internet searching and came up with a bunch of Met sites. As an aggregate, they indicate that the engine, transmission, brakes, steering, rear axle, and at least some of the suspension were straight carry-overs from the A30 and the A40. Given the Met's low selling price, small volume, and high parts-bin content, I just find it kind of hard to believe Nash or BMC would have tooled up an entire new unibody when they already had the A30's to work with. Having seen both up close (while lacking a measuring tape at the time), I'd swear the Met and the A30/A35 are the exact same wheelbase and track width. SignatureTeGGeR® > Your implication is that the unibody may be unique to the Met. I'm sure > you're right, but... Actually I'm not so sure, not being familiar with the British cars that the running gear was lifted from. It is common knowledge amongst old car buffs where the engine etc. came from, but I've never seen anything indicating that the unibody platform came from an existing vehicle. It would be interesting to compare the Met with an A30 or A40 close up, particularly underneath to check the chassis design. SignatureRoger Blake (Subtract 10 for email.) > Didn't pretty much every NA manufacturer move to single-piston floating > calipers by 1968? Well, Chrysler A-bodies (Dart/Valiant/Duster/Demon) stuck with 4-piston disks through 72, changing to Kelsey-Hayes floating calipers for 73. "TeGGeR?" <tegger@tegger.c0m> wrote: > Front drums were used by all world manufacturers well into the mid'70s, I don't know what was usual in those days. But I know that my parents' 1973 Opel Kadett (General Motors Europe) had front disk brakes. Since this was not an expensive or sports car, I would expect that front brakes were more the norm than the exception at the time. > along with single-circuit master cylinders where local laws permitted. I find this appalling ! Somewhate apropos I read an interview in the French Sport-Auto magazine with an old race driver. This guy used to drive for Lotus (50s or 60s). In that interview he said "Chapman was a genius but he always wanted to make things too damn light" (quote from memory). So during a race the brake line on this guy's car burst and since it was a single-circuit he lost all brakes. He managed to not hurt himself in the subsequent crash, but when he got back to the boxes he stopped at the Ferrari box and asked the team director for a place in the team. The next race he was driving for them. Signaturehttp://www.mat.uc.pt/~rps/ .pt is Portugal| `Whom the gods love die young'-Menander (342-292 BC) Europe | Villeneuve 50-82, Toivonen 56-86, Senna 60-94 >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 [quoted text clipped - 24 lines] > >discuss! It may seem surprising but not everyone considered them superior to drum. I recall an article back in the 60's in Popular Mechanics/Science. Smokey Yunich (probably misspelled) was one of there regular writers and had been, and perhaps still was at the time, a well known stock car racer. He believed drums were superior and wrote about it in a "debate" in the magazine with someone else who argued that disks were superior. There is something to be said for drum brakes, you'll notice they are still in widespread use on 18 wheelers. >> Or is this another thing where the rest of the world had 4-wheel disc >> brakes since the 1950s, but Detroit refused to 'progress'? [quoted text clipped - 10 lines] > drum brakes, you'll notice they are still in widespread use on 18 > wheelers. There is one area where drums are "better" - weight. on my 76 Camaro, the front disks are the heavy parts, and all that mass needs to be rotated. The rear drums are lighter than the rotors, and the total mass of the disk assembly is definitely greater than the total mass of the drum assembly. That said, I'll take the weight penalty with disks 11 times out of 10 on any car that I'm working on. I hate drums. I had a web page showing the weights, and it was around 40 pounds advantage for 4 wheel drums, but I've since lost the link, so don't quote me on that. Ray >>> Or is this another thing where the rest of the world had 4-wheel disc >>> brakes since the 1950s, but Detroit refused to 'progress'? [quoted text clipped - 25 lines] > > Ray I'm not sure that the weight thing is really that significant. If nothing else, the rotational inertia of a drum is likely greater than a disc of equal diameter, even if the total weight is the same or less. So you might win some on unsprung weight, but lose on rotational inertia. nate Signaturereplace "fly" with "com" to reply. http://home.comcast.net/~njnagel > I'm not sure that the weight thing is really that significant. If nothing > else, the rotational inertia of a drum is likely greater than a disc of > equal diameter, even if the total weight is the same or less. So you might > win some on unsprung weight, but lose on rotational inertia. > > nate I havent done any calculations, but intuitively it would seem that rotational inertia would not be greatly different, and wouldnt be too big a deal anyway. Have you put a pencil to it, Nate? |
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