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Author Topic: DD3 Brake Chamber rebuild  (Read 10298 times)
Gary LaBombard
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« Reply #30 on: July 30, 2006, 11:10:03 AM »

Cliff,
I have just one more question about this (horse beating subject), why isn't the DD3 used any more today on our newer rigs that go faster, haul heavier loads and go further distances than ever and over the same roads as the earlier brake systems used?? I don't mean to be so stubborn at this to keep it going but I truly don't understand why they aren't used more if they are so much more dependable and safer for the same reasons stated above?? As far as safety, I am all for that as you all know, but traveling safe speeds, traveling safe distances from the vehicle ahead of you having a safe braking system for your toad if used is being done by thousands of others right this moment is truly the way to travel and many of these buses do not have the DD3?? This is my last post on this so as not to bore you or peave you off on this but I can't help wondering. Are all the buses out there now with spring brake systems at a danger to the rest of us??

I finally am putting "MY" comments on this particular post to rest, thank God right??
Best of luck,
Gary
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Gary
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« Reply #31 on: July 30, 2006, 11:30:08 AM »

Gary,

I enjoy when we ALL get into a discussion on a subject like this.

Everyone is stating what they know, being cordial, expanding on each others posts as other information is added or commenting on

anothers post.

This is exactly how this BBS should be used.(My humble opinion)

I am also curious the reason why the change to the spring brakes.

My guess is that they were looking for a cheaper alternative that met there specifications. Or the specification changed.

Maybe the DD3 was considered overkill!

Of course this is not just with brakes , but all the componets of there assembly process

I would love to hear from someone who has first hand knowledge of the reason.

Interesting topic and I have enjoyed your contributions to it.

Cliff
« Last Edit: July 30, 2006, 02:50:50 PM by FloridaCracker » Logged

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Gary LaBombard
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« Reply #32 on: July 30, 2006, 02:55:57 PM »

Cliff,
You would make a good politician as you know the right things to say to calm down a Yankee-Rebel. Just don't get into politics, I like you as you are and you know how I feel about them right now anyhow. Maybe I will feel better when our troops come home before we lose any more and when the price of fuel comes down so that everyone can make a living and afford to get there to do it.

But I would seriously also like to know, why all the many millions of vehicles out there now all have the spring brakes and there are only a few old timers left, (Buses I believe only left now) that still have these dinosaur DD3's on them. Straight skinny now, no thoughts of how wonderful they were in the old days, straight stuff why they are not used today. Cost to manufactuer, not in an assembly factory once designed and parts fabricated in large lots, at least the cost would not be like we are led to believe. Good grief, 10 years ago you would pay abut $3,000 for a computer system that you can now buy for $499 at Best Buy. Why?? Competition which is great. Why can't these DD3's be manufactured in a competitive way or is it they are not really needed after all if you are safe.

Good grief, I said in my last post that was my last post on this subject but the (politician) here, (Cliff) calmed me down to more reasonable conversation, can't you tell??
Gary
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Gary
RJ
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« Reply #33 on: July 30, 2006, 06:21:15 PM »

Gary -  Simple answer to your question about why DD3s are no longer OEM on most equipment:


$$$$$$


Spring brakes are much simpler and less expensive, not to mention fewer air lines and associated plumbing. 

And, since the manufacturing philosophy nowdays seems to be more of "maximize the profit, forget the quality" (example: MCI's G4500), every penny saved makes the shareholders happy.  Not to mention the Wall Street analysts, who really screw the system up with their short-sighted short-range predictions.

FWIW. . .

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RJ Long
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« Reply #34 on: July 30, 2006, 06:41:39 PM »

Gary, I truly suspect that some bean counter somewhere along the way figured that spring brakes stop a coach half as fast as DD3s... but cost one-quarter as much. Or something like that. Choices like this get made all of the time. Same reason Ford execs took "acceptable risks" leading to exploding Pintos everywhere. And Morton Thiokol saved a few bucks on an o-ring that led to the Challenger disaster.

And, no, there's not a rash of motorcoach accidents due to failing air systems. Maybe spring brakes are "good enough" if they do fail. Or maybe loss of air pressure is almost non-existent anymore, especially in the well-maintained fleets of the daily haulers.

But I do know that a cyclist was killed in Boulder County just a few weeks ago due to failed brakes on a gravel truck. Similar accidents happen in the trucking industry all of the time, usually due to maintenence issues. And the most-advanced brake cans in the world won't stop a vehicle if the brakes are out of adjustment or over-worn.

What we can do, as a "pleasure" class of heavy-vehicle users, is maintain our coaches regularly, and deviate from the manufacturer's designs and specs only when the "acceptable risks" are tolerable and well-researched and engineered.

Speaking of deviations: Would I upgrade a Johnson Bar system to spring brakes? Most definitely. Would I retrofit spring cans onto a DD3 system? You already know the answer to that. Wink But someone else's "acceptable risks" might be different than mine.

And please don't make any post your last post on any subject, if you still have something to say. I learn stuff here every day from posters just like yourself who take the time to post information and ask meaningful questions. As long as we keep it civil... and I think we have here... we all benefit.

Cheers,
Brian
« Last Edit: July 30, 2006, 06:43:14 PM by SpaceShipBuffalo » Logged

Brian Brown
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« Reply #35 on: July 30, 2006, 10:17:23 PM »

Since there have been many viewpoints on this subject, I might as well add another.

When you lose your air so that the dynamite button pops, the springs on the drivers are released and provide as much stopping pressure as is required to cage the springs. On our coach, that is about 45 psi.

If you lose your air on a DD-3 system, and the button pops, then air is applied from a storage tank and the locks on the pushrods are set. What pressure is applied by the emergency air tank?

I ask this because I know that 45 psi represents quite a bit of stopping effort, but not as much as you would get from a full treadle application (over 80 psi). What is the chance of a collision or loss of control if that much braking effort were suddenly applied? We drive in icy conditions every now and then, and I sure wouldn't want them setting under those conditions.

Would the braking effort from a DD-3 system be much higher? What is the chance of a collision or loss of control with that pressure?

Maybe most of the above is academic, because most cases might involve some driver warning, and not be so dangerous. But I can think of some scenarios that would make loss of air pretty sudden. For example, what if a blowout ripped the hoses off of one pot? Would you prefer DD-3 or springs in a case like this?

The only kind of case that I can think of that I might want more pressure is if a hose blew when I was already standing on the treadle to prevent an accident. I would have to try to steer around whatever I was trying not to run into.

In most other cases, 45 psi would be more than I would care to have. What if the DD-3s applied a lot more pressure? It seems to me that a stackup on the freeway might be a real possibility, if there was no shoulder where this occurred.
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Tom Caffrey PD4106-2576
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« Reply #36 on: July 30, 2006, 11:12:11 PM »

If you lose your air on a DD-3 system, and the button pops, then air is applied from a storage tank and the locks on the pushrods are set. What pressure is applied by the emergency air tank?
Since the poppet is also supposed to apply the emergency brakes at 45psi on a DD3 system, I'd think that it would be the pressure of the emergency tank less the pressure on the service side diaphram of the can (albeit, rapidly decreasing in most cases). So, something like 120-45=75psi on the absolute high side to 90-45=55psi on the low side.

So, yes, the DD3's do stop the coach faster, because of the extra psi given at time of application over the 45psi you mention for springs. But, don't forget it's only applying the brakes to the drive axle cans (springs OR DD3's), whereas a treadle application applies to all axles, so stopping distances are even greater than the pressure would indicate. So I can't imagine a loss of control in this instance, esp. since the steering axle is unaffected. Unless you're on ice or slippery roads, like you said.

In most cases, however, I believe that I would want to stop sooner rather than later in an emergency air loss situation. Especially if headed downhill. Shocked

However, you do bring up some interesting points for discussion.

Thanks!
Brian
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Brian Brown
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« Reply #37 on: July 31, 2006, 05:35:00 AM »

To avoid a lot of mis-information, if you are working on DD-3 chambers go to

http://www.bendix.com/downloads/service_data_sheet/024600.pdf

for a detailed description of operation and repair. Pay particular  attention to the fact that all DD-3 30 chambers do not use the same diaphragms.
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RJ
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« Reply #38 on: July 31, 2006, 08:21:12 PM »

 Huh

Intelligent question designed as a dumb one:

Have any of you ever popped the emergency brake at 50+ mph to actually see what happens?   Shocked

I don't care if it's a spring brake or a DD3, if you've done it, what's been your experience?

If you haven't done it, why not?

Fire away!   Wink
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RJ Long
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« Reply #39 on: July 31, 2006, 10:36:12 PM »

If you haven't done it, why not?

Fire away! Wink

Sounds like a good thing to do... in the name of science, safety, and driver training. Why wait until an emergency to know how the coach will respond?

I'll give the poppet a pull at speed in the next few days and report back...
Brian
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Brian Brown
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« Reply #40 on: August 01, 2006, 06:18:32 AM »

I've pulled the e-brake on a dirt road at 20mph.  It locks up the drive axle NOW!  I personally would not do it at 50mph on pavement unless I had a set of tires I was ready to replace as the resulting flat spot on the tires will make for a very rough ride afterward.
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« Reply #41 on: August 01, 2006, 10:44:55 AM »

Correct me if I'm wrong, but spring brakes on trucks lock on both the trailer and both rear drive axles (where there are two rear axles). While a bus has only two emergency brake chambers for what could be more than half the weight of most trucks.
Any, or all, of the eight spring brake chambers will lock with loss of air...is the stopping force of a DD3 greater?
An aired up bus with DD3s won't roll off even if the park brake button was inadvertantly pushed, without releasing the park brake with the service brakes. Seems as though DD3s may have been designed with safety in mind? Just wondering why so many coaches were fitted with DD3s when trucks went to spring brakes? Got to be a story somewhere.
JR
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« Reply #42 on: August 01, 2006, 04:56:01 PM »


I've pulled the e-brake on a dirt road at 20mph.  It locks up the drive axle NOW!  I personally would not do it at 50mph on pavement unless I had a set of tires I was ready to replace as the resulting flat spot on the tires will make for a very rough ride afterward.



Brian - Try it on dry pavement at 50 mph - the coefficient of friction is quite different than dirt. . .   Wink
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RJ Long
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« Reply #43 on: August 01, 2006, 05:19:09 PM »

I did it once on my 80 Eagle which I assume had spring brakes. I did it at about 35 mph and there was no jerk, no skidding wheels. Just a short controlled stop.
Richard


I've pulled the e-brake on a dirt road at 20mph. It locks up the drive axle NOW! I personally would not do it at 50mph on pavement unless I had a set of tires I was ready to replace as the resulting flat spot on the tires will make for a very rough ride afterward.



Brian - Try it on dry pavement at 50 mph - the coefficient of friction is quite different than dirt. . . Wink
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« Reply #44 on: August 02, 2006, 06:04:12 AM »



Brian - Try it on dry pavement at 50 mph - the coefficient of friction is quite different than dirt. . . Wink

You know, if 20mph is okay and 50 mph is good, then trying it at 100mph is even better!  I gotta do that sometime.  I'll let you know when I plan to as the rocket assits on the rear of the bus to get to 100 should be very loud and visible for miles to come.  Sounds like fun!   Smiley
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