No, seriously... why are drum brakes "cheap"?

Maybe I have too much free time to think about things...

Just as an example (because it's what I drive) I was thinking about my 2013 Chevy Sonic. LS and LT trims get rear drums, while the LTZ and RS get rear discs.

I went to RockAuto and did some research:
Pads cost about the same as shoes
New drum is $65, new rotor is $30
Caliper is $130, wheel cylinder is $25
Hardware kit: $15 for drum, $8 for disc

So times two, disc brakes cost maybe $200 more in parts, at retail. Maybe $100 more per car at cost?

But then Chevy has to design, engineer, build, and stock two different ABS computers, two different sets of brake lines, and possibly two different master cylinders.

When does it stop being worth it?

Manufacturer math is x 000,000's. If it costs $5 less per car to do something that can translate into tens of millions over several years of a model manufacture. Also, there are higher premiums and prices for the higher trim models, so the profit margin on that amenity on those trim levels could translate into tens of millions in additional profit. You'll probably not be able to back into the tipping point without understanding literally every dime of the manufacturer's costing model.

I dunno. I am however ready for drums to go away entirely! Wasn't one of the excuses for keeping them around so long was that it was/is easier to get parking brakes to work with drums (leading to the bastardization on the rear of my '97 Explorer with a disc service brake and a tiny drum parking brake inside it)

EvanR wrote: But then Chevy has to design, engineer, build, and stock two different ABS computers, two different sets of brake lines, and possibly two different master cylinders. When does it stop being worth it?

THIS!

In reply to KyAllroad:

my 03 Toyota is the same way, the rotor hat is used as a little drum brake for the parking brake. Its annoying to deal with!

The new almost $40k Tacomas only come with rear drums.

I suspect some of the price difference may have to do with the precision / quality required for disc components. I am sure a drum, despite having about the same amount of metal, requires much more machining and precision than a disc.

I don't really mind drum brakes. Having some of the drum brake tools certainly makes it nicer. Heck, I am going to go through the brakes on my Ghia this weekend, and those requires manual adjustment!

Brian wrote:

EvanR wrote: But then Chevy has to design, engineer, build, and stock two different ABS computers, two different sets of brake lines, and possibly two different master cylinders. When does it stop being worth it?

THIS!

Not this.

The ABS computer is the same, the calibration is different- no cost. Most of the brake lines are identical up until the last bits- which can easily be made up via the flex line- no cost. And the braking effort can be made up via a different, but equal cost valve.

The other big deal about drums- they are much lighter. Which is a very big deal as we progress forward.

But I'll defer to Angry, since I'm not a brake engineer.

Also, my understanding is that drum brakes are usually lighter (at least in the rear) than discs. This is contrary to what you might think, but I remember that GRM converted their ACR project autocrosser back to drums in the rear and saved something like 10-15 pounds.

They are lighter and smaller. In rear applications they are much cheaper than the complicated caliper (or additional secondary drum) needed to have a parking brake. You can actuate them pretty effectively without hydraulic pressure at all. For heavy front bias vehicles the less effective braking isn't really an issue either. A FWD Malibu isn't using them for much.

I suppose for certain types of vehicles there might be an advantage to having the pad surface out of the weather although that is pure speculation I just made up.

No vehicle deserves to have drum brakes, not even Satan's own Hyundai.

Woody wrote: No vehicle deserves to have drum brakes, not even Satan's own Hyundai.

So if someone gave you a car with 4 drum brakes, you would turn it away, regardless of the car?

alfadriver wrote:

Woody wrote: No vehicle deserves to have drum brakes, not even Satan's own Hyundai.

So if someone gave you a car with 4 drum brakes, you would turn it away, regardless of the car?

Do you foresee that happening?

alfadriver wrote:

Woody wrote: No vehicle deserves to have drum brakes, not even Satan's own Hyundai.

So if someone gave you a car with 4 drum brakes, you would turn it away, regardless of the car?

Swap it to disks?

I wonder what the difference in assembly time on a production line is like...thinking drums have to take a fair bit longer to assemble.

Woody wrote:

alfadriver wrote:

Woody wrote: No vehicle deserves to have drum brakes, not even Satan's own Hyundai.

So if someone gave you a car with 4 drum brakes, you would turn it away, regardless of the car?

Do you foresee that happening?

No- hypothetical.

Bear in mind, there are already a LOT of cars with 4 wheel drums- and I know one that ran in the challenge like that.

Now that I think about it- I will, again, offer the idea that if you want to make a real change, there are opportunities to do so.

If it's actually cheaper, lighter, and more effective to have 4 disks, the math to make it happen is pretty easy to sell.

Furious_E wrote:

alfadriver wrote:

Woody wrote: No vehicle deserves to have drum brakes, not even Satan's own Hyundai.

So if someone gave you a car with 4 drum brakes, you would turn it away, regardless of the car?

Swap it to disks? I wonder what the difference in assembly time on a production line is like...thinking drums have to take a fair bit longer to assemble.

I'd think they get to the assembly line as brake/suspension assemblies. That is why they are attached to the hub with little clips or screws - so they don't fall off in shipping.

I like the Saturn method. Brake flex hose goes right to the wheel cylinder. WHy can't everyone do this?

FWIW, I am a staunch advocate of rear drums. They don't fail constantly like rear calipers, they are lighter, and they have far less drag. Modern rear drums also seem to outlast the rest of the car, you see Hondas and Toyotas with 250k on them and plenty of lining left.

For a drum, isn't there only one face to machine compared to two faces of a disk?

alfadriver wrote:

Woody wrote: No vehicle deserves to have drum brakes, not even Satan's own Hyundai.

So if someone gave you a car with 4 drum brakes, you would turn it away, regardless of the car?

Did he say that? No. He said that the vehicle didn't deserve it, not that they made the vehicle undeserving.

Having grown up driving - and servicing - a 3200 lb American car with unpowered drum brakes at all 4 corners, I agree with him completely.

RossD wrote: For a drum, isn't there only one face to machine compared to two faces of a disk?

Who still gets brakes machined in the days of Rock Auto and Amazon? At least for anything even remotely common.

Duke wrote:

RossD wrote: For a drum, isn't there only one face to machine compared to two faces of a disk?

Who still gets brakes machined in the days of Rock Auto and Amazon? At least for anything even remotely common.

you still have to manufacture the part the first time

In reply to Duke:

Alfas with 4 drums are awesome. Some, you can't even convert to 2 disks.

Bad drums don't mean they are all bad, just like live axles.

Even then, autocrossing a corvair with 4 drums was interesting- but still effective.

Again, if it matters that much- there are ways to change it. Math always wins the day.

I'm in agreement with your hatred of drums but Auto OEM's make critical decisions based on less than $1/per vehicle.

I have no problem with drums, it's those dammed bass players you gotta watch out for.

I don't like the comparison of drum to disc on the rear of a FWD econobox. One is significantly lighter, the other offers (or can offer) significantly more performance. Kinda apples to oranges.

Give the drums as much thermal mass and heat dissipation as the discs. They have to get a lot bigger.

Give the discs as little performance as the drums have. They can get a lot smaller & lighter.