When are disc brakes going to be the norm?

[allan5oh]

Other then upfront costs, I don't see any downside to them. Europe uses them exclusively. Whats the holdup? Are the big fleets really that resistant to newer better technology?

[Maniac]

They already tried them and they worked well , BUT didn't last long.

The company I was leased to has a yard full of old gasoline tankers with them, the mechanics said they were bad news, they used to change the pads every few weeks.

[allan5oh]

I've heard of the old design not working well either. The new ones are supposed to last longer and the pads are much easier to replace then shoes. I'd love to see the whole design in front of me and compare it to the current brakes. We all know how many problems there are with the current brakes. Clevis pins braking, s-cam rollers seizing and binding, s-cams wearing out, s-cam bushings wearing out. Some of this is preventable with maintenance, but not all of it.

[emerlin]

They are also much more expensive to rebuild than drums from what I've heard.

[Maniac]

The old ones were easy to change also, just had to do it often.

In 30 years I've never had any real brake problems, other than them wearing out, only replaced the "S" cam bushings on 1 trailer, must be my good maintenence that keeps them this way

[bob h]

The old ones were easy to change also, just had to do it often.

In 30 years I've never had any real brake problems, other than them wearing out, only replaced the "S" cam bushings on 1 trailer, must be my good maintenence that keeps them this way

sure it does ...

[allan5oh]

I don't know, I think drums are a severely inferior design in many ways. For example, up here we have problems with the s-cam rollers. They simply rust away, and bind up. I had a problem with my front axle pulling to the left, the stroke was the same and everything. Turned out one of the rollers was seized. How am I supposed to "maintain" that? It has to come apart to do anything. Those rollers don't get any grease.

[bob h]

I don't know, I think drums are a severely inferior design in many ways. For example, up here we have problems with the s-cam rollers. They simply rust away, and bind up. I had a problem with my front axle pulling to the left, the stroke was the same and everything. Turned out one of the rollers was seized. How am I supposed to "maintain" that? It has to come apart to do anything. Those rollers don't get any grease.

no, they don't. i do however grease them where they run in the shoe web

that sounds like a salt brine issue?

i've only ever heard bad stories about air disks; short life accompanied by high maintenance costs... i've never worked on equipment that had them.

in the shop, hydraulic disks on medium duties were quite expensive, and a short life..., i would expect the same with heavies.

are disks a better performing brake? yes

are disks more economical? no, and when disks do dominate the market, none of us here will ever see the price of brake maintenance (cost per mile) down where it is today again.

...but, they're comin' ;0)

[Birken Vogt]

Well from what I understand they will be coming sooner rather than later with the new stopping distance requirements. I too have heard nothing but bad about them, the various products by all manufacturers. I think that the good old 16.5x7" drums work great but I guess the stopping distance is not where the government wants it to be so we throw cautious driving out the window and replace it with gobs of money. Frustrating

Birken

[brian]

drum brakes can stop just as well as disc brakes, its the reaction time that differs but guess what there gonna be slow anyway in a 70 foot long 80k pound truck.

you can keep the decreased fuel mileage (disc pads are always touching the rotors in one spot or another and every little bit counts) and increased maintenance and cost of replacement.

[allan5oh]

drum brakes can stop just as well as disc brakes

I see *ZERO* evidence this is correct. Even the OEMS say that changing to disc brakes will be mandatory to decrease stopping distances.

Ever talk to a European driver that comes over here? They bitch about the junky brakes we have all the time. Lack of feel, brake fade, lack of brake power, you name it. The discs dominate the drums in those fields.

OK I'll rephrase what I'm saying, a properly designed disc brake owns drum brakes.

How many drum brakes do you see on performance vehicles?

[allan5oh]

Heres a good article on the NEWER disc brakes:

http://archives.fleetmag.com/publica...?pubId=1&id=49

and some quotes :

The biggest difference between the old brakes and the new DX models, according to Szapacs, is the way the brake actually operates on the slide pins that allow the caliper to slide freely on the rotor.

Big al likes! No more seized/rusty clevis's, s-cam rollers, etc..

Szapacs pays more up-front for the air disc brakes, but his trucks have more stopping power and maintenance costs on the DX 195s are, he says, "virtually nonexistent." Most of the units easily go 500,000 miles with no pad replacements or relines, and no rotor issues. Air Products trades its tractors out at 600,000 miles, and it's not uncommon for those trucks to be sold with their original pads and rotors up front.

Sounds pretty low maintenance to me.

The "overall design" of discs is definitely better. The problem in the past was with specific designs of the products. Hell, the first cars with EFI were pretty crappy. Funny, I don't see carbs any more.

[allan5oh]

Another manufacturer:

http://www.fleetequipmentmag.com/Def...&entry_id=2488

In fact, the company said all-disc truck tractors have consistently shown the ability to stop within today’s regulatory standard for passenger cars.

The impetus behind the NPRM on truck stopping distances is the Motor Carrier Safety Improvement Act of 1999, which was designed to reduce highway fatalities by 50 percent over the following 10-year period. NHTSA believes it can achieve this goal by reducing the tractor stopping distance requirement. Among its findings are that the difference in stopping distances between large trucks and passenger vehicles are a leading factor in the intensity of highway accidents. Currently, FMVSS provisions set the stopping distance for heavy trucks at 355 feet and at 216 feet for passenger vehicles. A 30 percent reduction would lower the heavy truck threshold to 249 feet.

That's fine and dandy, but there are vehicles out there that can stop in less then 100 feet. Also, that 249 feet is after the brakes have applied. Never mind reaction time, and the time it takes for the air to get to the brakes. You can see why better brakes are needed.

BTW, the "highway cowboys" should note the bolded word in that italicized statement. Not naming ANY names.

[allan5oh]

Threes a charm:

http://www.roadstaronline.com/2003/05/050a0305.asp

Also on the panel and giving the fleet perspective was Marty Fletcher, who is technical and training director for US Xpress. He had only good things to say about the 100-truck test with 50 ADB/ECBS tractors and 50 control trucks, with the air discs showing no maintenance issues, improved performance and, at 225,000 to 250,000 miles, only around 25% wear to the brake pads. At that level, they could go to a million miles, he said. However, Fletcher remains guarded. He says he wants to see what happens to braking performance when the pads get beyond 50% worn.

Regulation may be what will drive the use of the ADB - with or without ECBS - here. The National Highway Traffic Safety Administration is expected to issue a recommended performance rule that would call for 30% shorter stopping distances for heavy trucks by 2007. Today's braking regulation requires heavy vehicles to stop in 355 feet from 60 mph. According to Bendix testing, a typical drum-braked tractor with unbraked control trailer at 56,470 pounds GVW can pull up in about 292 feet, or 17% shorter. That won't be enough to meet the more stringent standard without further development of the basic S-cam brake.

But equipped with the air discs on steer and drive axles, the same rig can stop in 215 feet, or 39% shorter. Not only does that exceed the proposed performance target, but it is actually only about five feet more than a typical passenger car. As Bendix' Bailey points out, if the purpose of the regulation is safety, it makes a lot of sense to regulate trucks and cars to have comparable stopping performance.

And while there is no anticipated performance standard at 75 mph, there are plenty of states where trucks run at this speed. The disc brake's improved ability to covert kinetic energy to heat - without fade - is even more obvious here. In the Bendix tests, the drum-braked tractor-trailer stopped in 517 feet while the disc-equipped unit pulled up in 345 feet - just over the length of a football field - maintaining its better than 30% performance improvement and stopping 172 feet shorter.

[bob h]

Well from what I understand they will be coming sooner rather than later with the new stopping distance requirements. I too have heard nothing but bad about them, the various products by all manufacturers. I think that the good old 16.5x7" drums work great but I guess the stopping distance is not where the government wants it to be so we throw cautious driving out the window and replace it with gobs of money. Frustrating

Birken

nhtsa has already announced that the new stopping distances can be met by drum brake systems...

it is frustatating, the manufacturers are forcing this stuff onto the market, there's no money in 16.5 x 7s in anymore... anybody can market that stuff.

[bob h]

[quote="allan5oh"]

drum brakes can stop just as well as disc brakes

I see *ZERO* evidence this is correct.

agreed, too many variables... i dont' believe braking power is what drives disk brake interest anyhow

Even the OEMS say that changing to disc brakes will be mandatory to decrease stopping distances.

i don't see anywhere in the links you've provided where they claim disk brakeas are the ONLY way to meet new braking standards

Ever talk to a European driver that comes over here? They bitch about the junky brakes we have all the time. Lack of feel, brake fade, lack of brake power, you name it. The discs dominate the drums in those fields.

OK I'll rephrase what I'm saying, a properly designed disc brake owns drum brakes.

? maybe you should re-rephrase? ;0) ;0)

How many drum brakes do you see on performance vehicles?

[bob h]

drum brakes can stop just as well as disc brakes

I see *ZERO* evidence this is correct.

agreed, too many variables... i dont' believe braking power is what drives disk brake interest anyhow

Even the OEMS say that changing to disc brakes will be mandatory to decrease stopping distances.

i don't see anywhere in the links you've provided where they claim disk brakes are the ONLY way to meet new braking standards

Ever talk to a European driver that comes over here? They bitch about the junky brakes we have all the time. Lack of feel, brake fade, lack of brake power, you name it. The discs dominate the drums in those fields.

OK I'll rephrase what I'm saying, a properly designed disc brake owns drum brakes.

? maybe you should re-rephrase? ;0) ;0)

How many drum brakes do you see on performance vehicles?

[Birken Vogt]

nhtsa has already announced that the new stopping distances can be met by drum brake systems...

it is frustatating, the manufacturers are forcing this stuff onto the market, there's no money in 16.5 x 7s in anymore... anybody can market that stuff.

Yep, that is probably the most accurate assessment of the situation.

That's the way it goes these days it seems....

Birken

[allan5oh]

nhtsa has already announced that the new stopping distances can be met by drum brake systems...

it is frustatating, the manufacturers are forcing this stuff onto the market, there's no money in 16.5 x 7s in anymore... anybody can market that stuff.

Let's see, discs over drums:

- Decreased stopping distances
- Increased heat rejection
- Decreased fade due to design(a drum expands AWAY from the shoes)
- Increased "pedal feel" and sensitivity
- Less maintenance, if the system is properly designed

What is there to lose?

I don't think the manufacturers are forcing this stuff, we'll see what happens.

I think we should all at least try driving a full disc truck at some time. There might be quite a few pleasant surprises.

[RockyMtnProDriver]

It has been absolutely proved that disc brakes are superior to drum brakes in every way, except for cost. For all of the reasons why Allan said and more.

And the cost of them will certainly come down when they are in mass production.

We are going to have Discs on Class 8 vehicles for certain. It is just a matter of time.

I am certain that an 18 speed tranny is more expensive than a 5 and 4, that halogen lights are more expensive than standard headlights, that radial tires are more expensive than bias ply.

The only reason I did not get them on my tractor, is that that they are not available yet, and there is no where to fix them.

I think that those that say they don't want them probably also said they would never buy a touch tone phone, a color TV or get ABS on their car.

It is the future.