drum brake advantages

[moribundman]

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Hmmm... may be the rubber caps on the sliders' bolt heads were probably for better air sealing ?.. I was curious why there were rubber boots, and if for rust, why no boot for the bleeder screw.

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The rubber boots on the guide pins keep moisture out. Since the guide pins are lubed and stuck tightly in the caliper "holes," suction will naturally occur, which makes the sliding action springy.

The bleeder nipples have rubber caps.

 

[SWS]

Hi Audi,
I was thinking that disc brakes would work faster because there is essentially zero spacing of the friction components. Hit them with pressure and they brake instantly. Release the pressure and they free-up fast. This seems to me to be an advantage in the fast "pulsing" characteristic of ABS, for example.

Also, as previously stated by somebody, it makes sense that the ABS and VSC systems could be optimized if all of the brakes on the car are the same technology.

In terms of wet brakes, I have been driving for 33 years and have had several scares with wet 4-wheel drum brakes (including condensation). In contrast, my experience with disc brakes is that they don't stay wet. In 2 cars I have owned, the alloy wheels had large spokes so I could see and even touch the disc rotors. I have driven through terrible rain and puddles, splashing my way home and then parked right in the garage. I have examined the discs and they are dry. Touching the edge of the rotor (never the friction surface!), I observed that the rotor was warm, even if it was winter. Therefore, I have concluded that the combination of constant friction wiping and a little heat will keep disc brakes "dry", even in my worst driving. Note that I am not talking about submerging the brakes in water... that is a different worst-case scenario.

 

[jsharp]

The only advantage I can see to drum brakes is the ease of designing a parking brake mechanism.

A few people have mentioned the lower cost of drum brakes but I just can't see it. All of those drums, springs, levers, adjusters, cables, shoes, cylinders, backing plates, etc, etc. just can't be that much cheaper to build than a simple disc brake. And the assembly time and cost has to be substantially higher.

I'm starting to wonder if drum brakes aren't one of those "that's way we did it in '42, and it worked fine" things and that's why we still see them...

 

[JHZR2]

my 04 saab doesnt have drum parking brakes on its rear wheel discs.

There is actually a semi-rotating piston, which is attached to the parking brake handle. Using the lever actuates the rear disc brake calipers, and the pads clamping down act as a parking brake...

Works well!

JMH

 

[Steve S]

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Originally posted by Audi Junkie:
Drum's performance is not affected by wet conditions.

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unless they get wet.

 

[Steve S]

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Originally posted by Shannow:
Also, the air braking systems of big trucks lend themselves to drum brakes.

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I was lucky to be able to drive about 3 trips from San Francisco Calif to Salt Lake City Utah when I drove truck for Coca Cola U.S.A. .These trailors were setup for demo or testing I don't remember but they from a braking part worked good there was some real good grades to test them on. There was virtually no fade using the trailer brakes only

.The truck were loaded to their max which was close to 80,000 gross vehicle.

 

[John K]

jsharp - when disc brakes were becoming more common on European cars Detroit kept talking about there wasn't any advantage to going to discs, etc. The economics part comes from the investment they already had in manufacturing and they didn't want to invest in the change. The changeover is the expensive part, and in the beginning they didn't have floating calipers, etc. Detroit finds a way to lower the cost before adopting newer technology. Keeping what you have is always cheaper. Remember the PowerGlide 2 spd automatic? Chevy produced them for years after much better trannys were developed, because they had produced them so long and they were cheap to make. That is what amazes me about the Japanese, they will introduce newer designs of engines so fast. Other threads talk about the fact that DOHC aren't new, they have been around for years, etc., but they haven't been produced in great numbers until the
Japanese forced the competition to match them.

 

[darryld13]

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Originally posted by jsharp:
~SNIP~

A few people have mentioned the lower cost of drum brakes but I just can't see it. All of those drums, springs, levers, adjusters, cables, shoes, cylinders, backing plates, etc, etc. just can't be that much cheaper to build than a simple disc brake. And the assembly time and cost has to be substantially higher.

~SNIP~

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Calipers make the disc system more expensive. Drum=rotor, shoes=pad, but the caliper plus it's hardware is more expensive than the rest of the drum system. A good place to see the difference is RockAuto.com where you can price out a rear drum brake system versus an optional rear disc brake system on say a 2004 Accord LX.

 

[JHZR2]

very interesting!!!

Thanks,

JMH

 

[Audi Junkie]

I'd like to call-out the guys who claim drums operating in rainy conditions have pads and friction surfaces that are wet. I've seen reports of accumlated dust, not water though. I'm not looking for anything specific, just some general "proof" that they get wet...in the rain...on the inside.

 

[Chris142]

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Originally posted by Audi Junkie:
I'd like to call-out the guys who claim drums operating in rainy conditions have pads and friction surfaces that are wet. I've seen reports of accumlated dust, not water though. I'm not looking for anything specific, just some general "proof" that they get wet...in the rain...on the inside.

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Ok I'll bite.

My pickup has 4-wheel drums. After driving down a flooded street the 1st time you apply the brakes you don't know what to expect. It may go left, right or not stop at all.

Not a problem with normal rain but say if your waiting to turn right and your front wheels are in a dip then water will get into the drums.

 

[Chris142]

Big trucks use a "S" cam system which provides an enourmous amount of leverage to push the shoes against the drums.

The shoes are huge! They contact about 80% of the drum when applied vs 30% or so for disc brakes.

In cars the drum brakes will spin slightly when applied which applies even more pressure to the shoes than just the wheel cylinders supply.

This is wht you have 2 different sized shoes.

 

[Shannow]

quote:

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Originally posted by Audi Junkie:
I'd like to call-out the guys who claim drums operating in rainy conditions have pads and friction surfaces that are wet. I've seen reports of accumlated dust, not water though. I'm not looking for anything specific, just some general "proof" that they get wet...in the rain...on the inside.

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Audie Junkie,
my first car had 4 wheel drums.

In wet weather, they were generally OK (weren't even "good" in dry weather).

Hit standing water, and they were non existant. Unless it was a lucky day, and the fronts would take turns in locking (something to do with the servo effect and "stiction")

 

[Shannow]

I'd like to "call out" Audie Junkie.

Can you please point me to a seal generally installed in drum brakes that would prevent water under pressure getting into the brake drum ?

 

[dkcase]

I've never had a vehicle with 4-wheel disks and I drive the same way I learned and have always practiced -- when going through deep water in the road, lightly apply the brakes to keep water out of them. I guarantee if you don't you will know the difference.

Of course when disk brakes began to be popular that was one advantage claimed -- resistant to water effects because the water is spun right off.

 

[bulwnkl]

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Originally posted by JHZR2:
For a car that isnt 'racing' and at most will need to do a strong 80-0 stop, or a number of repeated 40-0 stops, with a number of feet of rolling between (like in speedup/stop and go traffic), is there any real advantage to rear discs?

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IMHO, no, there isn't. Just like there isn't a practical real-world advantage to a DOHC motor vs. a pushrod, nor to a 6-speed automatic vs. a 3-speed (or even the old 2-speed mentioned in this thread for many American-market cars).

Disk brakes are like carbon fiber; they're associated with "high performance," racing, and general "coolness," so they are a higher-priced option (or they come standard on a higher-priced model). I do actually believe that a decent rear disk brake system costs more than a decent rear drum brake system, which is not the case with carbon fiber, but that's another topic.

I do not know why Chevy went to rear disks and then back to drums on their pickups, but I sure hate many disk brakes on a working pickup. They are often the inexpensive single-piston sliding-caliper design, and they WILL NOT slide when you're operating in mud and serious dirt. I think the proper disk brake design is "too expensive" and so drums have been adopted once again. They also have lots more swept area and 1-time stopping power for huge loads.

 

[jsharp]

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Originally posted by darryld13:

quote:

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Originally posted by jsharp:
~SNIP~

A few people have mentioned the lower cost of drum brakes but I just can't see it. All of those drums, springs, levers, adjusters, cables, shoes, cylinders, backing plates, etc, etc. just can't be that much cheaper to build than a simple disc brake. And the assembly time and cost has to be substantially higher.

~SNIP~

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Calipers make the disc system more expensive. Drum=rotor, shoes=pad, but the caliper plus it's hardware is more expensive than the rest of the drum system. A good place to see the difference is RockAuto.com where you can price out a rear drum brake system versus an optional rear disc brake system on say a 2004 Accord LX.

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If you're using single acting floating calipers the brake hose is another thing that likely kills the cost vs. the solid lines you can use on a drum system. Some of that comes back to you in reduced assembly time though. What John K mentioned is probably as much the problem. The initial changeover.

Honestly, if I never got the chance to own or work on another drum brake I'd be happy. I expect the last pair of drum brakes built might have a self adjuster that actually works though...

 

[JHZR2]

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Originally posted by bulwnkl:
I do not know why Chevy went to rear disks and then back to drums on their pickups, but I sure hate many disk brakes on a working pickup. They are often the inexpensive single-piston sliding-caliper design, and they WILL NOT slide when you're operating in mud and serious dirt. I think the proper disk brake design is "too expensive" and so drums have been adopted once again. They also have lots more swept area and 1-time stopping power for huge loads.

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The will not slide in mud and dirt... yeah, I had some rear caliper issues on my 98 ZR2 for a long time... what is one of its primary uses? off roading, and often in mud and junk.

JMH

 

[Audi Junkie]

I did not say "submerged" or "water under pressure" I said "rainy conditions".

"My pickup has 4-wheel drums. After driving down a flooded street the 1st time you apply the brakes you don't know what to expect. It may go left, right or not stop at all.

Not a problem with normal rain but say if your waiting to turn right and your front wheels are in a dip then water will get into the drums"


This makes me think they stay dry during "rainy conditions".

 

[Shannow]

AJ, as I said.

if you drive through standing water, you can get water in the drums, and seriously affect braking.

That's NOT parking chin deep in a culvert...driving through a puddle at 40MPH can do it.

A far worst effect is when a single wheel locks in rainy conditions (particularly the rear). My brother spun twice due to this.