Originally Posted by DoorDing
I've never seen or heard of the maintenance and sizing issues you've described WRT rear disc brakes, but I'll take your word for it. I've never seen a brake disc (front or rear) in regular use that developed enough rust in the friction area that it wasn't quickly cleared after a few applications of the the main braking system.
You missed at least one e-brake system. I don't care for the goofy mini-drum setups, but plenty of systems use a cable to drive the main caliper. Those systems brake just as well as any rear drum e-brake system.
I also don't believe drum brakes are significantly more expensive to produce than disc brakes, or that manufacturers are doing anyone a favor by putting drums on less expensive vehicles, while using discs on higher end ones. I have no proof of that, other than what we see in model and trim level packages throughout the industry. Rear brake performance is far less important than front brakes, and if a manufacturer could cut costs by installing four wheel discs, I think that's all we'd see.
Marketing gets a bit weird in some situations, like paying a premium for superior performance. The lower end model may be equipped with the more expensive hardware just so you have to change up to the high end to get the perceived advantage (real or not). Marketing is all about manipulating the customer into giving you more money for less product. As I mentioned, in car and SUV applications where the rear load is consistent, rear disks do make sense, since they can be sized appropriately for the consistent load. Its with the swinging load, where a pickup can have a load on the rear swing by 1500-2000 pounds or more depending on whether it is empty or loaded to capacity. Some models of Tacoma have a 1500 pound payload capacity, and given that the majority of its 4000 pound curb weight is sitting on the front, that probably represents at or near two times the empty load on the rear axle, which means that you can apply a lot more braking force before it locks up.
Yes, most of the stopping power is from the front, but when you've got most of your weight sitting over the rear axle, you'd be surprised just how much stopping the back can do.
I've *owned* a pickup with rear disks and a MAJOR rear disk rusting problem. The rear disks had to be replaced on it every single year I owned it because it would develop massive bands of heavy rust. Before that truck, my previous had drums in the rear. 250,000 km and only ONE change of shoes. No other work done (just occasional checkups) on the rear brakes.
Not knowing where you call home, the rear disk rust problem may or may not be an issue there. The salt belts certainly experience this.
if a manufacturer could cut costs by installing four wheel discs, I think that's all we'd see.
That is, in fact, what you're starting to see. There are a few places where drums are installed as an intentional downgrade feature (among other downgrades and/or lack of upgrades) in order to push people into the premium model or upgraded package.
As far as Manufacturing expense goes, it is very easy to show that disks are cheaper to manufacture than drums. Just count all the parts! There is more material (steel is not cheap) on a drum than a disk, the machine required for cutting a drum surface is more complex and expensive. Even the physical shape of a drum is more complex to manufacture than a disk, most of which can just be cut out of a sheet. Both include a hydraulic slave cylinder with rubber seals and pistons, but there are a pile of springs and levers in the drum that aren't present in a disk.
So there you have it. Two kinds of brakes, both are good brakes, both have advantages and disadvantages. The key is to use it in the place where it is best suited. Sometimes, the wrong one goes into a place, just because there are so many people who have this unfounded impression that one is better than the other. Yes, disk brakes are better than drums, however, only in the specific applications where they actually are.