Why did it take so long for auto manufacturers in the US to put disk brakes on their cars. They are superior and I can’t see how they could cost much more than drum brakes to manufacture and install.
Alot of things don’t cost much more. Add them all up, and they make a dent.
BTW, my truck has anti-lock brakes and the rears are drums. Since 90% of the braking is handled by the fronts, it isn’t a big deal. After 85k, they are 50% worn.
Most likely experence w/ them. Also front disk/rear drum usually is very well ballanced combo. Most of the braking force is handeled w/ the front anyway, while you don’t have the constant drag losses of disk in the rear (drum brakes do not have a constant drag).
A general rule of thumb when you’re talking about cars is that the industry will adopt new technology and standards after they have already been around for a long time. They resisted putting seat belts in cars for years until the government threatened them with regulation. They then adopted seat belts as an option. Same with airbags, disc brakes, fuel injection, ABS and taction control. By the time they were put on cars they were already old technology. A consumer does not want to be a test-bed for new stuff. Wonder why GM doesn’t have any hybrid technology? It’s because they were letting Toyota take the risk. Now they’re behind the times, but they were not at all certain that hybrids would be successful. Toyota took a risk and won. GM took a risk and lost.
Now there is more oversight and mandate from the government, but there’s still a lot of play in the system. Some cheaper cars are still rear drum- front disc brakes, and that’s OK because the rear wheels don’t do a lot of the work. If the government tried to mandate discs on the back they would fight it tooth and nail, because they make money selling the option.
Think about this: if the actual difference in price between drums and discs is 5 cents, over the life of a successful car design (say 200,000 cars) they stand to lose $10,000 over the course of production. That adds up over time when you count every option and every model, because they all have compromises. Then you factor in the loss of profit from the upgrade, the installation costs for options, the engineering, etc., and you’re talking the difference for some companies between solvency and bankruptcy.
Another point to note is that hydraulic assist is required with disc brakes; these days, when powered accessories are the norm a manufacturer scarcely gives a second thought to adding another hydraulic system, but back in the days when drums were common, adding discs also means running additional lines and fittings. Disc brakes first become common on passenger cars in sport cars and high performance touring cars where brake fade (then tendency of brakes to loose resistance as they heat up) can be an issue. The more open and exposed surface of discs cools much faster, and unlike drums making them larger makes them more effective both at generating braking force and radiating away heat. The discs, however, are also more sensitive to tolerances; even a slight warpage or surface roughness will result in shudder and squeal, so they need to be composed of a very uniform material and held in line with the caliper to fairly high tolerance. So there’s both some legacy experience and technical know-how that contributed to inertia with regard to the widespread adoption of disc brakes. I have a hard time imaging that the drum mechanism is cheaper than discs, but the additional equipment and tolerances may bring the two into parity with regard to cost, and if you’re already using drums on other cars in your line it’s pretty easy to spec them for a new model.
That being said, I’d rather replace the discs and pads any day over working on drums. Discs are bloody simple; two pads, a caliper assembly, a piston or two, all bolted to the hub. Drums are a spiny-arsed porcupine in comparison, with endless amounts of springly little bits that like to go “boing!” all over the garage.
Here’s the How Stuff Works page on power brakes. Share and Enjoy.
Stranger
I always wondered the same thing until I drove my Saturn with rear drum brakes. It is absolutely the best braking car I’ve ever driven and that includes a number of luxury sport cars. By best braking I’m referring to feel and control. Certainly an ABS version might improve wet surface braking but I’d rather have these brakes. I’m taking the ABS system off my sports car and putting on bigger brakes in hopes of duplicating the feel.
Negative on that. I had a brand new 1966 Mustang GT which had front disc brakes, rear drums, and NO power assist. This is NOT a requirement.
You’ve never seen the movie, have you? 
I don’t know the complete history of disc brakes, but I can give you a little bit of info. One of the first automotive uses was in race cars built by Harry A. Miller who was the mentor of Preston Tucker. I think that they first appeared in the 1930s, during WW II, military aircraft were equipped with disc brakes. (It was also at this time that improved hydraulic technology was developed, which was needed to control aircraft like the P-51 Mustang.) After the war, Tucker was the first person to try and build a car with disc brakes, but he had problems with the brakes being cooled, and then, of course, the Feds got involved and he got shut down.
Given how long it took the automotive industry to adopt any of Tucker’s ideas, it’s not really surprising that disc brakes took so long to be implemented. A note for folks with disc brakes on classic cars, if your car was built before steel belted tires, using steel belted tires on unmodified cars can create vibration levels which can dislodge the calipers and cause nasty problems. (It’s such a serious issue that the Studebaker Drivers Club will disqualify you from appearing any events with such a set up.)
[Minor hijack] 90% front 10% rear never struck me as smart distribution of braking force. In those vehicles with adjustable proportioning valves, I’ve set them to provide closer to 60/40. [/Mh]
A couple of things here.
First off is Rick’s law of building cars (I know it called Rick’s law, cause I just named it)
The way you make a million dollars in the car business is to save $1 per car and build a million of them
Simple huh?
Contrary to what the OP posted, when disc brakes were new they were not cheaper, they were more expensive, way more expensive which meant that they broke Rick’s law. Car makers are in business to make money as much as possible, so they adhere to Rick’s law as much as they possibly can.*
a couple of other things to keep in mind, first off cars were lighter then, speed limits were lower, and manual transmissions were a much larger portion of the model sales mix back in the 1950s when disc brakes were starting to show up in imported cars. In addition there was an entire training and supply issue to address. Drums had been around since Moby Dick was a minnow, parts were available everywhere, and everybody knew how to service them. When Disc brakes were new nobody knew how to service them. ** All of these factors helped the drum brake stay in dominance until the mid to late 60’s when muscle cars came on the scene where with the extra power, the extra braking was needed.
after that it became a matter of marketing, then need. Features from “muscle cars” started to trickle down to other models to give them the cachet of the muscle car. Think hey my Maverick isn’t a Mustang, but it has disc brakes just like the Mustang! After that, the perception became (rightfully so in this case, IMHO) that if you did not have disc brakes, you didn’t have shit, and low and behold now everything has at least front disc brakes.
- In general if you want to know why something is done on a car, the answer can be found by looking at one of the following reasons:
[ul]
[li]Rick’s Law[/li][li]Customer demand[/li][li]Regulation[/li][li]Tradition at that car company[/li][li]Conscience of the car company[/li][/ul]
Examples:
why did my 50’s car have real crome metal trim, and now my new car has crome plastic? Rick’s law.
Why do cars have standard power windows, and A/C? Customer demand
Why do cars have Air Bags? Regulation
Why do Peugeot and Renault use 11mm head bolts when the rest of the world uses either 10mm or 12mm? Tradition. Either that, or because they are French. Beats me.
Why did Volvo install 3 point seat belts in our cars starting in 1959? Conscience. (The president of our company had a wife who was a nurse working in rehab. She used to insist that there had to be a way to lower injuries in car crashes. So he hired Nils Bolin, the 3 point belt was invented, patented, and the rest as they say was history, so it was conscience. Either that or nagging.
)
**Believe me when I got into this business in 1968 there were plenty of shops that would either not service disc brakes, or had just gotten into that business in the last year or two.
I doubt you could find a car that uses 90/10 as the distribution from the factory. The rears would never wear out, and the front would be needing replacement all the time.
Huh? Hydraulic assist?
Power brakes use vacuum for the assist (with the exception of a handful of cars 30 or so years ago that had the “Powerboost” system).
Disc brakes do not require assist. Plenty of small cars have non-power disc brakes.
Adding disc brakes does not require additional lines and fittings to speak of. With a disc/drum system, the additional components needed were a metering valve and a proportioning valve. Metering valves were often built into the master cylinder or combined with the porportioning valve. Proportioning valves were typically in line – it might require changing a 4-foot line into a 1-foot line and a 3-foot line, but it certainly didn’t require “another hydraulic system.”
IANAM, but I believe one of the problems with disc brakes was the emergency brake. There’s a nifty mechanism in drum brakes for incorporating the emergency brake. Not so w/ disc. I’m pretty sure it took them a while to incorporate the emergency brake function into the disc design.
Right. With a disc/drum system, it’s easy to put the parking brake in with the drum portion. With 4-wheel disc brakes, the typical choices for the parking brake are using more complicated calipers or having little “parking brake drums” inside the discs, either of which involves extra design and hardware compared to a disc/drum system.