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Author Topic: Intelligent Dumb Question:  (Read 14986 times)
Devin & Amy
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« Reply #15 on: August 04, 2006, 05:46:43 AM »

Hi all,

Forgive my ignorance, but if I have a sudden air loss at highway speed, won't the E-brake pop?
 I had a situation similar to this except not at highway speed. I crowned a mountain at a campground close to Lebanon,TN when I "felt a pop in my foot". coming down the other side of the mountain I noticed that my pressure went below 70 p.s.i. w/o the accompanying rattle of my compressor kicking in. I took it slow to the campground knowing I was hurt and not wanting to fix the bus on a two lane highway. I entered into the campground at about 20 p.s.i. and almost got into a site, when the e-brake set at about 5 m.p.h. it hit pretty hard.
The compressor had internally combusted and had to be replaced. But if I would have lost an airline or anything else catastrophic in the system, do you have any time to think, or just react?
Again sorry for my ignorance, as I've been pretty lucky with a good sound bus.

Devin
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« Reply #16 on: August 04, 2006, 07:54:14 AM »

Russ,

You are one funny fellow!

Yes, I have aplied the parking brake at high speed.

And when this experiment is over, we need to go back and make some correction to some of these other posts.

Folks, don't be using this post as education, there are some myths being exposed.

happy coaching!
buswarrior
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« Reply #17 on: August 04, 2006, 01:35:27 PM »

buswarrior,

If these are myths how about telling us exactly which ones are?

A general statement helps nobody, please be specific.
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PD4107-152
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« Reply #18 on: August 04, 2006, 05:51:06 PM »

Gusc (and others) -  Hang in there, I want this post to run thru Sunday evening, then I'll explain the method to my madness!

Promise!   Wink
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RJ Long
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« Reply #19 on: August 04, 2006, 07:52:31 PM »

OK, I posted this in another thread, but thought it might be better "out on it's own", so to speak.† So here it is:


Have any of you "popped" the emergency brake button at 50 mph on dry pavement to actually see what happens?


If so, please share your experience.


Yes;   I had a front tire blowout about a year and a half ago.   I remembered that in the drivers book
         for my MCI,  It said that I could do that in case of emergency.    When I had the blowout,
         I did apply the parking brake.  Everything went smooth.  The bus stayed on the road and
         everything was under control.  The only thing that was a bit unerving was the way the bus
         shook.  I mean everything . Even had a couple of seams split on the cabinets.  But all was
         OK.   Check page 9  (approx)  in the MCI drivers hand book.    Just keep good tires  on the
         front end and all will be OK.   Good luck.

If not, why not?


Let the flames begin!!† †Wink












PS:† There's actually a method to my madness here, be patient. . .
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Barn Owl
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« Reply #20 on: August 04, 2006, 11:26:56 PM »

Warning! This post will probably be come across as disjointed and seem to ramble on, but itís late and I am tired, so at this time I donít care. I might clean it up later if I feel like it.

Iím not going to pretend to know it all; I think there are a lot of members here that have been driving longer than I have been living. I have to supplement my lack of experience and knowledge by consulting others. I have only driven my bus, so Iím not sure what all buses are capable of. I do have a CDL and several years ago I did drive professionally (not buses).

Quote
it's physically impossible to lock up a drive axle carrying 7 or more tons with an e-brake application... esp. at 40mph. Good grief.

I know that spring parking brakes do not have the ability to lock up a fully loaded set of drive axles but they can if you donít have enough weight on them. I donít like to type so that is why I said if one ďmanagedĒ to lock them up and that saved me from having to delve into every possible scenario. Would an empty shell do it? I donít know, but I stand by what I said that if you did or could lock them, it can be expensive if you flat spot your tires.

I am fortunate to work with a very large company that has one of the fewest accidents rates per mile driven. Their training program is often emulated and copied. I have never seen anything on practicing this procedure. Our instructors do not teach this, and if there was a benefit to it, Iím sure they would.

I talked to several of our tractor mechanics about it and they also see no reason or benefit to doing it. Part of their preventive maintenance procedure is to test the parking brake. This is done by engaging the brake while the vehicle is stationary and attempting to move it. I had never heard about cam over so I asked: They said that in the ďold daysĒ there was a style that was prone to it if the brakes were not adjusted properly, but no one here (where I work) is old enough to have seen a set like that I† guess. They also said that the only time they have seen a cam over in modern brakes is when there has been some type of brake component failure. An example was given of a cracked or broken brake drum that would allow the shoes to hyper-extend up over the cam. By the way, the four mechanics I talked to said they would not pull the parking brake while moving in a bus if they owned one, even though it would probably not do any damage to the components.

Also as luck would have it our state DMV uses our lot to test for the CDL license. I asked about the DOT pre-trip that was mentioned in an earlier posting about testing the parking brake at low speed. I was told that in the state of VA there is no such requirement, and the official had never heard of it (Does someone have a DOT web link that references this?). She said that she sees no real benefit to doing it.† The same driving methods and recovery methods are essentially the same for all vehicles. The example given is that if you can recover from a skid in a car you should be able to recover from a skid in a bus using the same techniques.

There are situations where one needs to be exposed to certain situations. When I was getting my pilots license part of the training was to expose the student to a stall/spin. This would allow one to recognize the dangerous situation and recover from it. I see the value of that. Pulling the parking brake at 50mph for kicks and giggles, Iím not getting. If it was proven to be beneficial then it would be a common practice.

Now Iím not against it, Iím to easy going to be.† If itís something someone wants to do, and they feel better after having the experience and knowledge of what happens after you do it, then thatís wonderful. My point is that if you donít, I do not feel that you would be placing yourself at some sort of disadvantage vs. those who have.

Quote
Hang in there, I want this post to run thru Sunday evening, then I'll explain the method to my madness!

Promise!† †

I'm waiting to see if I am falling into some type of trap.
« Last Edit: August 08, 2006, 08:30:26 PM by Barn Owl » Logged

L. Christley - W3EYE Amateur Extra
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Happycampersrus
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« Reply #21 on: August 05, 2006, 04:52:25 AM »

Hey, Barn Owl

The reason I posted the "cam over" is because alot of folks on this board have some really old buses such as the 4104's and Senic Cruiser's and some older than that. I am not going to get into a pissing contest with all the folks here, But I have took my little bottle jack and fixed cam over problems as recently as last year. My company that I work for has some old equipment and some newer stuff. I don't have the luxury of having all new stuff.

Now on to the next topic. I have yet to find any pretrip inspection that says to drive a vehicle down the road and pop the parking brake or emergency brake and that search also includes the states of Cal. & Fla. All I have read say just what Barn Owl describes.

Oh well guys do it your way, as I have missed something about this brake test. A little background on me is I have worked on farm and heavy equipment since the 70's. I graduated from Nashville Auto Diesel College in 1992, and have had class A's since 1993.


Dale
« Last Edit: August 05, 2006, 05:27:03 AM by Happycampersrus » Logged
JackConrad
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« Reply #22 on: August 05, 2006, 05:29:48 AM »

   Perhaps I should explain my pretrip air brake test.  Not sure if it is exactly as DOT requires, but here is what I do. I build air pressure to 120, release parking braking, and put bus in gear letting bus creep to insure that parking brake is released. I then shut off engine, make a firm service brake application, let air pressure stabilize and hold for 1 minute to see if there is any pressure drop. Then continue pumping brake pedal until parking brake "pops", noting this pressure (on my bus this is usually  between 45-50 PSI). I then start engine and let air pressure build, noting how long it takes to build to 120 (mine takes a little longer because I have added an additional accessory tank). I then put bus in gear and try moving before releasing the parking brake. This procedure also alows me to see what pressure activates the low air alarm and at what pressure the alarm de-activates.
   Speaking of low air alarms, how many have both audible and visual low air alarms in working condition. I have been in several coaches lately that did not have working low air alarms SCARY!   Jack
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« Reply #23 on: August 05, 2006, 07:24:05 AM »

Whew !
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Barn Owl
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« Reply #24 on: August 05, 2006, 07:52:31 AM »

I was glad to learn about ďcam oversĒ because I am getting my education here on this board (Iím not sure if my 4106 is susceptible yet). I am lucky to have at work about 15 fleet mechanics to consult with (The best part is its free!), so when I hear something on this board that I want to know more about or I have a problem, the first thing I do is take my question to them. The old man who ran the airport where I learned to fly (He had thousands upon thousands of flight hours) drilled into all of his students that no matter how much you know, or think you know, you are always a student. This has served me well, and if I ever was a student, I am now more than ever. Thank you all for all for the time you take to share your knowledge and experiences with the rest of us. Have a great weekend everyone.

BTW: My low air alarm is INOP so I added that to my list. Thanks Jack
« Last Edit: August 05, 2006, 07:55:39 AM by Barn Owl » Logged

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« Reply #25 on: August 05, 2006, 07:54:32 AM »

Also as luck would have it our state DMV uses our lot to test for the CDL license. I asked about the DOT pre-trip that was mentioned in an earlier posting about testing the parking brake at low speed. I was told that in the state of VA there is no such requirement, and the official had never heard of it (Does someone have a DOT web link that references this?).


Right here is from California's: http://www.dmv.ca.gov/pubs/cdl_htm/sec10_a.htm
Under parking brake check: "Allow the vehicle to move forward slowly and apply the parking brake or set the brake and try to move the vehicle. The brake should not allow any movement."

Why the option? I suspect for some vehicles, it's easier on the clutch to test the park brakes when rolling. But either test accomplishes the same thing... to know that the parking brake will hold the vehicle on a grade when stopped.

Mr. Conrad's pretrip test is exactly what we should all be doing every time we start up our coaches to go somewhere. I, for one, will admit that I don't always do it.

While some might read this thread and think that Russ and Buswarrior are being coy and evasive... but I believe that their years of training coach drivers intends for discussions like this to make us all really think about (and for some of us, actually discover) how our braking systems work and respond in an emergency situation. And I'm pretty certain that Russ was not advocating that everyone go out, get their coach up to speed, and pull their parking brakes. But this discussion has opened up some very important dialogue about our coaches most important safety systems... and that's a very, very good thing, IMHO.

Brian
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Brian Brown
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Longmont, CO
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« Reply #26 on: August 05, 2006, 08:14:45 AM »

As an ex-truck driver of 27 years and around 3.2 million accident free miles, most as an owner operator, I will wait to make any comments on the advisability of "dynamiting" the brakes at speed, "cam-over", the ability of a loaded set of drivers with spring brakes to lock up the wheels, or the actual number of spring brakes on a semi-tractor until Russ hangs the final word on us in his experiment.

This has been an extremely infomative and useful thread so far, let's see how many can glean something from this.

Dallas
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rwc
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« Reply #27 on: August 05, 2006, 08:46:37 AM »

While I have done lock up the brakes om motorcycles to see which way they want to slide so I would be prepared in an emergency I am not sure I would want to do this in a bus. I think that the pre-trip test as described above would be best.
   I get the impression that a "CAM OVER" is not a good thing but what exactly does this describe??
 Thanks for the enlightenment
    RWC
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Happycampersrus
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« Reply #28 on: August 05, 2006, 10:01:08 AM »

What happens during a cam over is simple an often times caused by worn or improperly adjusted brakes.

The brake shoes are driven by the brake camshaft. It has a S shaped end on it. The cam is turned and the S contacts the rollers on the shoes, spreading them apart to apply the linings to the drum, thus applying the brake.

A cam over is when the S cam is driven to far on the rollers. Sometimes the slack adjuster has to be removed to put the cam back in place. Worn rollers, Worn linings, and Worn drums or drums that have been turned to much can cause this situation. Todays brake shoes have larger rollers to help prevent this and larger rollers are available to replace yours upon doing a brake job. CHANGE THE ROLLERS EVERYTIME you do a brake job even if they look good, replace them.

If you keep good brake maintenance you probably won't ever encounter this problem.

Dale
« Last Edit: August 05, 2006, 10:07:37 AM by Happycampersrus » Logged
gus
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« Reply #29 on: August 05, 2006, 03:47:35 PM »

I would never test spring brakes under way, at barely rolling speed it is bad enough. Of course in a real emergency I might try anything, but not just for a test.

The older GMCs, of which I have one, had an ICC brake button for emergency application of the rear brakes only. These are air brakes, not spring, and all the books say not to use this for a parking brake-for obvious reasons. I have never read anything in the operating manuals about testing these while at speed.

Locked up rear wheels can take you off the road unless the brakes and the road surface are perfect, not likely in the real world.
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