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Old 01-25-2021, 03:34 PM   #41
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Quote:
Originally Posted by Caplansail View Post
I passed my NY Class B CDL this morning with the Schoolbus endorsement. I mentioned more on my decision to get the CDL elsewhere in the forum. I’m a good, reasonably conservative driver, and there is no way I would have routinely taken the time for a full precheck (or really learned it). Getting the CDL [U]made[U] me learn how to do things the safest way. I’d like to add that I have 100 times more respect for big rig drivers than I have ever had.

Now I just need to get my AZ bus to start when it’s cold.

Barbara
Congrats Barbara on passing the test!
Someone once said, Knowledge is power.
And 100 times more respect to you for making such an effort.
Cheers
Stay safe

Oscar
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Old 01-25-2021, 03:51 PM   #42
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Quote:
Originally Posted by Caplansail View Post
I passed my NY Class B CDL this morning with the Schoolbus endorsement. I mentioned more on my decision to get the CDL elsewhere in the forum. I’m a good, reasonably conservative driver, and there is no way I would have routinely taken the time for a full precheck (or really learned it). Getting the CDL [U]made[U] me learn how to do things the safest way. I’d like to add that I have 100 times more respect for big rig drivers than I have ever had.

Now I just need to get my AZ bus to start when it’s cold.

Barbara
Well, how excellent! Good for you, Barbara. As far as your bus goes...maybe it just misses Arizona? I laugh as I read and write this, because I'm in Arizona and I just got done plowing snow for the second day in a row. Even the chickens are taking shelter inside. So, I'm not sure if my own buses would start today, without having plugged in the block heaters.
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Old 01-25-2021, 04:16 PM   #43
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Originally Posted by rossvtaylor View Post
Well, how excellent! Good for you, Barbara. As far as your bus goes...maybe it just misses Arizona? I laugh as I read and write this, because I'm in Arizona and I just got done plowing snow for the second day in a row. Even the chickens are taking shelter inside. So, I'm not sure if my own buses would start today, without having plugged in the block heaters.
Holy 2021!! I'm supposed to be plowing snow tonight and I'm outside in a T shirt feeding the chickens and enjoying a cold one, think I might need to mow the lawn before I head to work!! We have a river/beach area not far from our house that many local nudist's frequent and there were even some hardcore types out there Saturday.
definitely a George Castanza type day
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Old 01-25-2021, 04:27 PM   #44
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Here is some science behind Pulse and glide vs riding the brakes..

The drums / rotors have mass. Brake fade occurs when the temperature of the pad / drum reaches a point where friction reduces.. that temperature point which matters is where the pad and drum are mated, nowhere else.

By riding the brake you heat that point up and while the mass of metal tries to carry the heat away it cannot do so fast enough so things get hot. You ride harder and that mating surface gets hotter.

When you pulse hard then let offf you creat a quick and sharp temp rise in the mating surfaces.. letting off allows the heat to redistribute within the rest of the drum and reduce the temp of the pad and the drum both. Now you have a “fresh” shot you can stab again.

This also allows you to get a good “feel” on the health of your brakes that you will lose if you simply ride them.


So you start out very slow at the top of the hill and use your brakes sparingly. As you go down you can allow your bus to gain some speed as you pulse the brakes. You still generally keep it slow and in a lower gear yes even with an AT545 you can keep it slow enough to stay in 2nd or 3rd and will have some engine braking.

The slow speed affords you another reserve which is the mass of your bus. If you hit a very steep part of the grade down you can allow the bus to gain a little speed as you were already going well under the maximum sustainable speed.. so you may be at 25 mph, stab down to 20, allow up to 27, stab down to 22, allow up to 29, stab down to 24,etc..

Dissipating the energy and inertia of the moving bus is the name of the game . The faster your bus goes the more energy it has stored up ..

The uphill before hand is your best friend in dissipating energy.. creating the hill at a very slow speed and with almost ice cold braking surfaces is the ultimate tool for navigating down the other side.
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Old 01-25-2021, 10:24 PM   #45
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With the AT545 you need to be slowed down enough before it will drop into the lower gear you have selected. You will be going slow enough that when you drop into gear your engine will not rev high, more about mid range.

You need to be familiar enough with the transmission to know that you have slowed down enough and that you are actually in the gear you selected.

Next thing to know is that if you start down a hill at low rpm the transmission often does not engage or maybe disengages, starts freewheeling, when you recognize this you have to get on the throttle to reengage. If you are in really steep country this gets kind of exciting because by the time it reengages it is time to get on the brakes!
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Old 01-25-2021, 10:50 PM   #46
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Remember me?

Well done, folks.
We do have some real knowledge in this bunch.

Most of our buses have drum brakes, yes, that is all there is to it. And drum brake-shoes are mechanically adjusted, one "click" at the time -- even if the "automatic slack adjuster" works, which is a true novelty after a handful years.

When I taught this stuff in the trucking company class-room, we used a video from a brake manufacturer (Rockwell? Eaton? I don't remember which. Maybe somebody can find it online. [I can type faster than I can search, so....] )

The video emphasized how... no two drum brakes are ever likely to be adjusted exactly the same, and certainly not four (or more) of them.

With... let's call it "1 brick" on the brake pedal, the tightest brake will engage a bit and the other three not at all yet. Leave that one brick on that one brake long enough, and that brake will first stop braking and eventually erupt in fire.

Two bricks might start the second brake working a bit, and so on.

But if you stack 20 bricks on the pedal, all the brakes will each be doing a pretty fair amount of the work.

Do this for a few second, so you reduce the speed maybe ten Miles Per Hour very approximately – from high engine RPMs to low RPMs, in the same gear.

Then let them all cool – put your bricks (feet) on the dash (figuratively speaking) and just watch the tach. This being drum brakes, there is even some air circulation between the shoe and the drum, provided you take all the bricks off the pedal.

Repeat, yes.

Starting down the hill at "ridiculously" low speed in the first place is vital, yes.


Again, back in another life....
Sometimes I took a rookie to the DMV for his Commercial Driver License test – not my own trainees.
Most – most! – of them flunked before they were even allowed to put the transmission in gear. They flunked the air brake part of the pre-trip vehicle inspection.

And even if you can learn by rote to perform the pre-trip steps in correct order, it means little for traffic safety if you do not understand – comprehend – the what-how-&-why of what you are inspecting.

There can be only one reason why Air Brake Endorsement is not required for RVs. Wait... two reasons: money and votes.

The typical RV owner is a well-to-do senior citizen couple – "Ma & Pa Kettle", but with more $$$. They throw money at the RV industry like it burns in their pockets, and they vote. No State or Federal legislator will ever dare offend them by telling them they don't already know how to drive. Air brake, schmeer brake – this puppy has a 32-inch laser-bomb TV with full-color espresso dispenser!

Not a thing to do with traffic safety.


Finally, a Tale From The Dark Side.



(Evil sound-effect plays – bwuahahahahahah....)

It was this time of year. Frosty at night.

Ashland Grade is a pretty good sporting drop-off on I-5 with a couple well-used Run-Away Truck Gravel-Traps, from Siskiyou Summing at 4,310 feet elevation to the Shakespeare Festival center of Ashland, Oregon, at 1,949 feet in a handful miles. Winding, too.



Evening. Snow flurries. Water running across the road here and there. Water not running where shade had kept the sun off the pavement in the afternoon.

As usual, my 18-wheeler was grossing around 76,000 pounds – might have been 46,000 pounds of tomato sauce on 20 pallets, conceptually speaking.

13 gears, and I started down that grade in a gear quite far down in the single digit.

I call this "hanging the truck on the engine". A low enough gear that the engine, with full Jake Brake on -- meaning maximum possible compression braking – maintains a steady speed with both my feet on the dash. Maximum compression braking happens at maximum engine RPMs – close to redline. Loud.

Suddenly, the roaring noise stopped.

A heart-stopping quiet.

Engine, clutch, transmission, drive-shaft, rear axle, wheels, tires... were idling.
I was sledding down Ashland Grade on water-no-longer-running.

What to do?!

(Hint; Free Bird knows.)

ANNOUNCER: Stay tuned for the next exiting episode of As The Wheels Turn, Or Not on most of these stations.

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Old 01-26-2021, 12:07 AM   #47
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ANNOUNCER: And now... for your listening pleasure from coast to coast, and all the ships at sea, this Special Presentation of the exiting finale of As The Wheels Turn Or Not, starring Some Fool Truck Driver.

In our last exiting episode, Some Fool Truck Driver was sledding down Ashland Grade in the nose of 46,000 pounds of ketchup, with a darn good possibility of adding his own 200 pounds of ketchup to the load at the bottom of the hill, or sooner.



What to do?!

SMART-ALEC SIDEKICK: See that punctuation mark made up by combining a question mark and an exclamation point? This is called an interrobang.

(Sound-effects man slaps a shoe into a pillow, as Orson Welles (photo above) kicks Sidekick away from the microphone.)

What to do?!

Yup. Grab a whole fistful of gears all at once and slam the accelerator to the floor.
Spin those tires back up to match the rapidly-increasing speed of the road, so they have a fighting chance of regaining rolling grip.

And it worked. I am typing this – I ain't an extra case of tomato sauce, scattered along Interstate 5 on Ashland Grade, under a wafer-thin layer of water-not-running.

ANNOUNCER: And there you have it. Understanding how your vehicle actually works... works.

Silent Radio Theater is a sponsored by... (jingle plays)... Elliot's Portable Bicycle Service & Piano Lounge – a proud sponsor of Silent Radio Theater and other silliness of dubious renown.

We now return you to our regularly scheduled exiting programming, in progress.

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The "Black Death" of the 14th century killed half the population of Europe and Asia.

Please blah, blah, blah.
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Old 01-26-2021, 12:43 AM   #48
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Awesome Elliot!
Thanks for the great spin and the brick analogy is awesome for the layman.
And yes fully agree with you on the two reasons for air endorsement not being required.
It's not exactly the same here in BC, I am required to have it for my class one CDL, motor home operators are required to have it also but anyone from the US in a motorhome or bus holidaying here is not required if it's not required in your registered home state.
Thanks again for the story
Cheers

Oscar
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Old 01-26-2021, 03:30 AM   #49
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ANNOUNCER: Good evening once again all you boys and girls out there in radio land, and all the ships at sea.
By the overwhelming demand of a listener just like yourself -- although, one named Oscar -- we now proudly bring you a Command Performance of a Bonus Episode of As The Wheels Turn Or Not, starring Some Old Bicycle Mechanic, sponsored by... (drum roll)... MaryAnimal's Foot Salon & Body Painting Studio.

NARRATOR: Our story begins one August in 2017...

SMART-ALEC SIDEKICK: How many Augusts were there in that year?

(whoomp, as before)

NARRATOR (tries again): ...in August that year, when one Elliot – of recent infamy hereabouts – was loading up Millicent, his skoolie bus, with all the Stuff for a certain Burning Man camp.

And that was not all. He was loading a second bus with even more Stuff!

VARIOUS INCONSEQUENTIAL ACTORS WHO HAPPEN TO BE LOITERING IN THE STUDIO, HOPING FOR THEIR BIG BREAK: Oooooooo!

NARRATOR: Several camp-mates were assisting, and one of them, Bob, was scheduled to drive the second bus.

Having never driven a Large Vehicle With Air Brakes before, Bob was looking forward to a spin-around-the-block with Elliot, to learn how to drive all over again -- Bob also being from Canada.

However.... Bob, being as well an enterprising and universally-competent and unflappable gent, simply took off on this familiarization run all by hisself while said Elliot was in the house.

And... returned... slightly shaken.

TECHNICAL GUY: In your average car and pick-um-up-truck, the brake pedal is hinged at the top, behind the speedometer, and to apply the brake you step on the bottom end of the pedal, which is conveniently festooned with a rubber pad for your pedicureal comfort.

However, in a Large Vehicle with Air Brakes, the brake pedal is hinged at the floor, and you must stack the bricks on the top tip of the pedal for any significant reduction of velocity to occur.

NARRATOR: Bob, of course, figured this out on his own.

(pregnant pause)

Eventually.

(Bada-bing)

ANNOUNCER: And now a word from our sponsor.

JINGLE SINGERS (a vocal group who works for free to gain experience in live radidio):
"MaryAnimal had a little lamb -- EE-I-EE-I-OH!"

DIRECTOR (heard in the background): You're fired.

JINGLE SINGERS (still singing): "Can't fire us, you little ham – 'cus we don't work here, yo!"

PITCH MAN (rushes to the microphone, minimizing embarrassment): Let MaryAnimal's Foot Salon take good care of your dusty and rusty podiatric extremities with a sloppin' good application of Dr. Fraud's Snake Oil For Dry Footsies And Cracked Bicycle Tires. Two chairs, no waiting. Balloon tires slightly higher.

(embarrassingly long pause, anyway)

DIRECTOR (whispering): More!

PITCH MAN (ad-libbing): Let MaryAnimal's Body Painting Studio spruce up your flabby belly with a dazzling lightning bolt or two! Fast-drying yet reasonably-non-toxic paints in many colors. Artists are standing by, Noon to six daily! Art-work is limited only by your imagination – or not even that! Rally your rump and boost your boobies with any design of your choosing, or ours.

(longer embarrassing pause)

A NEW VOICE, in a stern tone: The owners and management of this station would like to apologize to our listeners for the preceding unfortunate....

(click)

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Old 01-26-2021, 07:25 PM   #50
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One clarification:
I would never have wise-cracked about "Bob" being from Canada, if I did not have the greatest respect and admiration for all my Canadian friends. My comment was meant entirely affectionately.

I often do similar with Norwegians, and I am one myself. Same concept.
In this case, I meant to recognize and honor Oscar1, whose profile shows him to be in Canada.

Thank you, all!
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Please blah, blah, blah.
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Old 01-26-2021, 08:21 PM   #51
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Quote:
Originally Posted by Elliot Naess View Post
One clarification:
I would never have wise-cracked about "Bob" being from Canada, if I did not have the greatest respect and admiration for all my Canadian friends. My comment was meant entirely affectionately.

I often do similar with Norwegians, and I am one myself. Same concept.
In this case, I meant to recognize and honor Oscar1, whose profile shows him to be in Canada.

Thank you, all!
Haha! Absolutely no offence taken here at all. I can assure you being called Canadian is not the worst I've been called. Apparently we do say thank you, sorry and "eh" a little too often but most of us have thick skin and can take a joke like the best of them.
Thanks again Elliot and keep up the good work.
Cheers

Oscar
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Old 01-26-2021, 10:07 PM   #52
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Brakes are over rated. All they ever do is slow you down and grind progress to a halt....................
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Old 01-26-2021, 11:17 PM   #53
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You may have heard of Ettore Bugatti, the Italian-French builder of fabulous cars, especially his splendidly fast race cars, back "in the day".

Legend holds....
A British customer came to France and picked up his new Bugatti sports car, but soon returned and complained to Mr. Bugatti that the car had weak brakes.
Mr. Bugatti dismissed him out of hand: "Ai build my cahrs to GO!, not to stop!"
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Please blah, blah, blah.
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Old 01-26-2021, 11:56 PM   #54
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Loss of brakes is BAD BAD BAD!!!

Quote:
VAN BUREN, Ark. -- Nine people were killed Saturday when a runaway truck rammed a station wagon carrying seven family members and both vehicles crashed into a drugstore, causing an explosion that damaged a half-block area.

On June 21, 1985, a little before 8 p.m. that Friday night, an 18-wheeler loaded with frozen pork steaks lost its breaks and barreled down Log Town Hill in Van Buren AR. The truck went airborne after hitting the railroad tracks at the train depot.
https://www.upi.com/Archives/1985/06...7814488260800/

I was in that area three days before, it still brings me to tears thinking about it

No trucks have been allowed down that hill since
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Old 01-27-2021, 01:54 AM   #55
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Thanks to all who posted further with more info!



Quote:
Originally Posted by Oscar1 View Post
Attachment 53210
This is my office every day. heavy trucks, steep mountains and the sh*ttiest conditions. This is the Coq (Highway Thru Hell) I know what works for me and it works for everyone else if applied right. Im not here to debate this any further but a big beef I have is your very first response to the OP was not accurate but stated like you knew the answer, only later revealing that in fact you are not a commercial operator and have little experience in this matter. This does a great disservice to the new members and new drivers and is dangerous. How about next time start your response with
"hey I'm not a commercial driver and don't have an air brake endorsement but my opinion is"
Stay safe

Oscar
This is a fair enough complaint. My response is that I wasn't giving advice based on "commercial driver", or, specifically, "air brakes" (yea, I know the OP said air brakes), but I was giving generalized advice that I thought to be true. As I later stated, this was advice given to me when I first learned to drive, for passenger cars with hydraulic brakes. There was also no doubt in my mind someone would immediately chime in contradicting me. And I mentioned right at first, my point is not standard advice.
But driving is what I love to do. I have a lot of experience driving all over the country, but I live in one of the most hilly parts (as I mentioned). And I gotta say, I have never seen an 18-wheeler drive like that (speed-up-slow-down-speed-up) on any hill, even when I hang with them in my bus going slow - we all just do 30MPH or slower on big hills.
I would surely "pulse" my speed like that in the conditions you drive in (in that picture), and go even slower downhill; for traction, methinks. Not overheating.


Comments here have surely shown me the greater importance of knowing my air-brakes better - not to be "endorsed", but a better driver and vehicle owner. Would those deep-down-nitty-gritty comments have come out without such a (knowingly, and statedly so from the beginning) controversial statement that I made? I've heard "get to know your air brakes" since I got the bus, and blew it off - it will come with time I thought. Now I, at least, have been convinced that is about as near foolish as I want to admit.....



Quote:
Originally Posted by RamRod4 View Post
Ahhh so thats what the "master cancel" button is for

AHHHH! You're killin' me mon!


======================


I gave up on the idea of showing the math. If you didn't understand the theories of energy conservation and inertia and rocket science in the first place, what good would the math do? And if you do understand them, the math becomes pointless; you should get my point anyway.


But here's more of my comments on this matter:



Quote:
Originally Posted by Seriousracer View Post
https://wanderlounge.net/wp-content/...8/07/PI221.pdf

Heat causes expansion also causes gas build up on the friction material surface. So less friction material contact means faster wear,faster brake fade and more heat building up quicker. The last one is hard to understand but it is the truth. Less lining to dissipate heat back into. So the leading edge of the lining holders all the heat.
The air brakes need to be adjusted correctly for any of this to work.
Learn how to check and adjust your brakes.


OK! I didn't yet read the article, but you answered the question I had in my mind (I think):

heat must dissipate faster than gained at the pad surface to cruise downhill at a given speed, or average speed if you are "stabbing"/"pulsing" your brakes. This is a function of the force of gravity. (saying nothing about stopping, which is most important - go slow!)


One other reason I gave up on the math was not knowing how to model heat dissipation in various different materials. But in my mind, the only way the "pulse"/"stab" method would be more effective is if heat dissipates at an exponentially greater rate with time. If the pad material expands as it heats, and shrinks as it cools, combined with the "riding on air" effect heating up the leading edge more which amplifies this expansion/shinkage, then heat dissipation would likely change also, with heat "flowing" slower when expanded.


I was thinking heat typically dissipates linearly with time, or perhaps even exponentially slower with time.


It was a busy week (so I'm just now getting back to this). Got some welding done; cut some metal with those black abrasive 10" saw "blades" (don't waste your $$$ on any except DeWalt blades like this - I tried most of the popular ones, and none come close to DeWalt's longevity and quality); drilled some big holes in said metal.



I noted some things:


My welder has a "duty cycle" that is "X" amount of minutes in any given 10 minute period. For example, at 100-amps, it is 20%, or 2 minutes on, 8 off, 2 on, 8 off; or it could be 1 on, 4 off, 1 on, 4 off, 1 on, 4 off; etc. This suggests to me a linear dissipation rate of heat with time. At 50 amps or below, I get 100% duty cycle.


If I compare brakes to a welder, we see that the steeper the hill, the slower you must go, because heat is building faster, and needs time to dissipate. But it also suggests that if you add heat all at once in a burst, or slowly, there is a maximum limit to the heat and it doesn't matter about how long it cools in between any given 10-minute segment of time. The duty rating and the amps rating both increase linearly as shown on the face of the welder.


When I cut the metal, it gets hot. RED hot. Gotta keep my fingers a ways away from the cutting line, or they burn. Just by looking/feeling, it "seems" to dissipate linearly throughout the piece of metal, but that is subjective, not science. It takes a few minutes to cool enough to handle. The cutting blade edge, however, I can touch the moment the blade stops spinning. If I had a helper, I'd get them to use an infrared thermometer to measure the blade tip while actually cutting; but I think the result would be skewed by metal particles stuck to it. I can see it glowing with red speckles as I cut, and sparks hit my faceshield. My point though, is that it does not get too hot because, it seems, it does not conduct heat. Any hot particles are simply the ones that are wearing off at the moment as they cut the metal.



Brake pads do not "cut" metal, they grind it off (same thing really), but still "in my mind" they are heat-conductive-resistant. Semi-metalic pads would conduct more heat than ceramic. With hydraulic brakes, this is important, because heat buildup can boil the hydraulic fluid and your brakes get "squishy" suddenly, and the pads can't get enough pressure to stop the vehicle any longer. I'm thinking brake-pad material is the same basic material for drums/rotors/hydraulic/air, but I could be wrong on that. All that was part of my original thinking.



When I drilled holes in the (thick) metal, I used a drill-press. This gave me very subtle and precise control of the pressure on the bit tip. I used penetrating oil to lube/cool the cutting surface. If I used light pressure, just enough to scrape metal dust into a pile around the spinning bit (it's getting dull, sharpened once or twice already), the oil was fine. I could do that for minutes at a time. But the moment I used harder pressure, the oil smoked. Didn't matter if I started cold, with a puddle of oil, and jammed right into cutting, or if I "pulsed" it on/off, or if I "rode" it at a lower pressure and then pressed harder. It smoked the moment when I pressed hard, and stopped the moment when I lowered the pressure. Again this suggests a linear rate of heat dissipation though time, and appears to support my original claim. But as we've seen since my last post, there is more to my original claim than I saw then.


Quote:
Originally Posted by rclark48 View Post
In the event of overheating, you're left with the engine braking (which on a diesel without a compression brake or exhaust brake is not as strong as a gas engine since there's no throttle plate choking the engine--regardless of loose/no lockup torque converter),

...


On the topic of overheating brakes, while the total friction/heat generated going down the hill is the same (for a given speed), the brakes are better able to dissipate the heat with cycled braking. Yes, pads/shoes will glaze over, but "brake fade" actually has more to do with the drums. When drum brakes (more common on busses and CMVs for many years) are applied, the friction lining of the shoes actually heats the drums which in turn attempt to dissipate the heat to the air/wheel/axle/whatever it can--the shoes aren't what dissipates the heat. As the drums heat up, the diameter grows (this is where all the slack adjuster talk becomes relevant) and the shoes have to be actuated farther to maintain pressure against the drum. Eventually, if the drum grows too large from too much heat, there's just not enough travel in the shoe actuation to press anymore against the drum and the brakes begin to "fade". So while it's true that the shoes actually stay really close to the drum, that's only the case when the properly adjusted brakes are cool. As they heat up, the clearance increases and some air could snake past the baking plate to cool the linings--but it's still the drum that's the key. One reason that drums have a maximum allowable diameter when turning them has to do with the shoe actuation travel. Other reasons include reduced strength/heat capacity (don't want them to burst either). Disks and pads are less susceptible to fading since the calipers are attempting to squish the disk vs expanding a drum.

Now, the reason that the cycled braking works better can be easily illustrated with cooking. If you've ever cooked with an oldskool, cast iron pan, you'll know that it takes a while to heat it up and a while to cool down. Brake drums (heavy and usually cast iron) act the same. When you apply the brakes, the drums absorb heat like a sponge. When you let off, the heat drips out--and you have to give it some time to drip out because you can't wring it out like you could a sponge. If you're riding the brakes all the way down and constantly putting heat into them, you can get to the point that you're putting the heat in faster than the drum can leak it out to the atmosphere--just like a sponge under a constant faucet gets saturated and can't soak up anymore water. Some old trucks actually had water tanks with drains that the driver could open up to flood water over the drums to cool them off (since water can absorb heat faster than air) if they got hot.

Another note for people thinking that a locking torque converter will solve the problems, many automatic transmissions unlock the converter when coasting or when not in highest or second to highest gear. If you've geared down appropriately, there's a good chance you're not even in lockup anyway.

Thank you for this info. Excellent points made. I never thought about the diesel's lack of a throttle plate as a limiting factor to engine braking. Damn thing takes 2 batteries just to spin to start, so...hopefully that is enough.



My only critique is that the iron-skillet metaphor doesn't jive. At some point the pan will heat up to a maximum point in a given fire-pit (based on placement and the heat in the coals). Same with the brake drum on a given hill. If you don't want to burn your food, use less coals, or space your pan away from them. You don't take it in and out and in and our and in and out of the fire. If your pan is too hot it must cool away from or out of the firepit, but ideally you set up the firepit to get the pan to be the optimum temp and keep it there while you cook. On a hill, you have to go slow or it is like putting that pan on the hottest of coals. If you "pulse", it is like putting your pan on coals twice as hot for half as long.


Water tanks to cool the brake drums. Interesting, but seems I remember my bro in Jackson Hole telling me how brakes get hot riding (or pulsing) down that big hill from the pass I mentioned previous, and then they hit the puddles from snowmelt and it warps their rotors. Seems it would do that to drums a bit also.


Quote:
Originally Posted by cadillackid View Post
The drums / rotors have mass. Brake fade occurs when the temperature of the pad / drum reaches a point where friction reduces.. that temperature point which matters is where the pad and drum are mated, nowhere else.

By riding the brake you heat that point up and while the mass of metal tries to carry the heat away it cannot do so fast enough so things get hot. You ride harder and that mating surface gets hotter.

When you pulse hard then let offf you creat a quick and sharp temp rise in the mating surfaces.. letting off allows the heat to redistribute within the rest of the drum and reduce the temp of the pad and the drum both. Now you have a “fresh” shot you can stab again.


All correct, but missing my original point, seems to me, at least: the rate of heat in must be higher than the rate of heat out for the brakes to overheat. If you don't create a quick sharp temp rise (by riding your brakes with a less pressure on the pedal / brake-surfaces) the metal has time to dissipate the heat anyway. If you get to going too fast and need to stop fast, that sharp spike will be high enough to start overheating those surfaces before you can release the pressure for a cooling period.



Quote:
Originally Posted by cadillackid View Post
This also allows you to get a good “feel” on the health of your brakes that you will lose if you simply ride them.
This is one of the points I was thinking that makes the "stab/pulse" method better.


Also, the "stab/pulse" method "exercizes" your brakes so if they are getting icy or otherwise "sticky", they can hopefully be loosened into functioning correctly.


Another point I wanted to make about the "stab/pulse" method is that for commercial drivers, you may be driving a different weight load, with a different trailer or even tractor with brakes that respond just a little different, and every hill is always different from the last. We bus owners get to know our bus and how it handles based on its unchanging weight, and with experience, we can tell (just as in a car) how the vehicle will respond to a hill just by looking at the road as we drive. But with a load that varies, you need to get the "feel" for each hill. How fast is that vehicle accelerating between brake "stabs"? If it is too fast, you better slow down to an even slower average speed.


And Elliot made the last point that I was thinking of: a non-working brake at one wheel or unevenly adjusted brakes.

Quote:
Originally Posted by cadillackid View Post
The slow speed affords you another reserve which is the mass of your bus. If you hit a very steep part of the grade down you can allow the bus to gain a little speed as you were already going well under the maximum sustainable speed.. so you may be at 25 mph, stab down to 20, allow up to 27, stab down to 22, allow up to 29, stab down to 24,etc..

Dissipating the energy and inertia of the moving bus is the name of the game . The faster your bus goes the more energy it has stored up ..

The uphill before hand is your best friend in dissipating energy.. creating the hill at a very slow speed and with almost ice cold braking surfaces is the ultimate tool for navigating down the other side.


I boldened the part that says it all. That speed is where you overheat your brakes. Don't come close to that speed.



My brakes on my truck locked up one time, on a front wheel. (I forget why, clogged hose probably - I was still a teen and clueless about mechanics then). Pulled hard to the left. Silly me went and touched the rotor. YEA! But they never got to the point of fading. Maybe I didn't drive it far or down a big hill before fixing it (I know I was fearlessly dumb as a kid, and drove my 5-speed manual-tranny Honda with only the E-brake for a while, due to lack of funds. But I wasn't the only one in my high-school doing that)


The pads that did fade on me were the cheepo-creepo $9-per-set "organic" pads. Those were the ones I mentioned in a previous post with my lil' old 1983 Toyota 2WD pickup. All the posts by different folks about the metal drums and rotors and how they are affected still hold. These pads just couldn't handle the high-heat. And they sucked for a stopping distance even when cold.



Quote:
Originally Posted by Free Bird View Post
Next thing to know is that if you start down a hill at low rpm the transmission often does not engage or maybe disengages, starts freewheeling, when you recognize this you have to get on the throttle to reengage. If you are in really steep country this gets kind of exciting because by the time it reengages it is time to get on the brakes!
Need to know info. Thanks!


Quote:
Originally Posted by Elliot Naess View Post
The video emphasized how... no two drum brakes are ever likely to be adjusted exactly the same, and certainly not four (or more) of them.

With... let's call it "1 brick" on the brake pedal, the tightest brake will engage a bit and the other three not at all yet. Leave that one brick on that one brake long enough, and that brake will first stop braking and eventually erupt in fire.

Two bricks might start the second brake working a bit, and so on.

But if you stack 20 bricks on the pedal, all the brakes will each be doing a pretty fair amount of the work.

Do this for a few second, so you reduce the speed maybe ten Miles Per Hour very approximately – from high engine RPMs to low RPMs, in the same gear.

Then let them all cool – put your bricks (feet) on the dash (figuratively speaking) and just watch the tach. This being drum brakes, there is even some air circulation between the shoe and the drum, provided you take all the bricks off the pedal.

Repeat, yes.

Starting down the hill at "ridiculously" low speed in the first place is vital, yes.


Again, back in another life....
Sometimes I took a rookie to the DMV for his Commercial Driver License test – not my own trainees.
Most – most! – of them flunked before they were even allowed to put the transmission in gear. They flunked the air brake part of the pre-trip vehicle inspection.

And even if you can learn by rote to perform the pre-trip steps in correct order, it means little for traffic safety if you do not understand – comprehend – the what-how-&-why of what you are inspecting.

There can be only one reason why Air Brake Endorsement is not required for RVs. Wait... two reasons: money and votes.

THIS IS THE ABSOLUTE ANSWER I was looking for. Not only did you win a prize (a box of Crackerjacks, but I took the toy inside - couldn't help it!) for best and most scientific answer (and with no math or rocket science theoretics needed!), you get another prize for the "entertainment factor" (a used lottery ticket that was never checked for the winning numbers).


I gotta say, you, Elliot, are a real bonus to this site. High praise for your contributions herein. Why are you hiding in a bus? You should be doing SNL or Comedy Central.


I forgot to mention how I was also bashed on this sight for simply being a man; not a MCP or something. Just a male. So pitiful.


YOU< Elliot, are one of the reasons I came back again and again.

(and my bus needs help sometimes)

One final thing: if your brakes go out and you can see the bottom of the hill and the road is strait and not blocked or choked with traffic, just hit the bottom and cost to a stop. It's when the road has curves, or you need to stop that the problems happen. Your only hope in that case is to start slow, and proceed slow.



I'm done. Aloha
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Old 01-27-2021, 08:45 AM   #56
Skoolie
 
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Quote:
Originally Posted by Mountain Gnome View Post


I'm done. Aloha

I hope that does not mean you are quitting the forum because your feelings were hurt. Sometimes it is embarrassing to be proved wrong on a public forum, oh how I know this, but it should be taken as a learning opportunity. How you respond to the new info will determine your level of respect going forward.



As with most things in real life, brake procedure is not something that can be put on a spread sheet or proven in a simulator program. There are sooooo freak'n many variables that come into play here. (insert captain obvious smiley) Heat dissipation applied to braking has variables such as ambient temp, air speed across and around the braking surfaces, sinking material properties, wheel design, mud flap and aerodynamic diverters, etc., etc.



I've been around long enough to remember the old way of constant and steady application. It actually was an accepted method way back. But then, air brake technology was also just getting started in the commercial truck industry. Trucks with a diesel engine were just gaining popularity. 160hp was a thing of the future back then. Brakes were smaller. regulations were non existent. Over loads were common. Knowledge of procedure and proper engineering for the regulated load sizing were yet to come.


Technology over time has brought about a ton of new metallurgy and new composite materials, which in turn have changed many procedures and acceptance of regulations. It's also changed how those fancy educated theories are applied. Computer modeling and R&D has about as many fails as it does successes. Real world application R&D never ends. Computer simulated R&D ends when the program was put into production and has limits based on such.


I hope you're not considering leaving the forum.
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Old 01-27-2021, 12:49 PM   #57
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Quote:
Originally Posted by Mountain Gnome View Post
No, thank you for disagreeing. That is what makes this a better place. No one here has all the answers, and I am not a pro-driver with that experience.



What if you don't have an engine brake, like me with an AT545? No lockup converter, no can downshift.


Then you said it at the end....my whole point: go slow.

IDK, they said when I was in school I was smart...kids cheated off me. I never "felt" that way, but physics was so simple to me, I was skipping 32% of the days (max # I could without failing), smoking buds, rebelling like a teen, but I still made "A"s in those classes. And from what I remember, the total amount of heat generated is a factor of mass and gravity. A set amount of heat-generating friction is required to balance the force of gravity - no more - no less - to maintain speed downhill (remember, some friction comes from the wind-resistance, also), doesn't matter how fast that speed is maintained. But then there is inertia also, and if you are going fast in the first place, gotta overcome that to slow down. Pulsing the brakes concentrates that friction in a limited amount of time. Gotta spread out the time....go slower....
Reconsidered and deleted my post. Think I'm gonna keep my mouth shut
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Old 01-27-2021, 02:18 PM   #58
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Location: Hillsboro Oregon
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CDL downhill braking history. To back up my previous claim of once accepted steady pressure.

Crash forensics
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Old 01-27-2021, 02:21 PM   #59
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Quote:
Originally Posted by Deezl Smoke View Post
I hope that does not mean you are quitting the forum because your feelings were hurt. Sometimes it is embarrassing to be proved wrong on a public forum, oh how I know this, but it should be taken as a learning opportunity. How you respond to the new info will determine your level of respect going forward.

I hope you're not considering leaving the forum.
No, not feeling are hurt if I am proved wrong. That would make me "dumb". Was I proved "wrong"? To some (most) extent, yes. Good thing. Makes me smarter.


And now all who read this know WHY I was wrong, and to me, that is more important than simply knowing the answer - like (I forget who) said in an earlier post: people might memorize the steps in checking your air-brakes for driving a commercial vehicle, but they don't necessarily understand why....


"WHY" is always more important than "DO". I used to argue with my dad about that when I was 8 or 9. "When I say jump, you don't ask 'why', you ask 'how high'". How does that teach me anything? Anyway, if I asked why, I usually only got anger. He sucked. Glad he left.



When folks want to bash others for being wrong, it turns me off. Doesn't "upset" me, but disappoints me. Unhelpful to any. Pitiful in my eyes.

Quote:
Originally Posted by kidharris View Post
Reconsidered and deleted my post. Think I'm gonna keep my mouth shut
I only wonder if this is what I'm talking about.


But when folks want to bash others for their personal choices or for who they are, I admit it makes me very "upset" even when it does not apply to me, and when it does apply to me, well... That is my "weakness" and flaw that I should work on. And with life being totally challenging to me far more than ever before, emotionally, these last 3-4 years (personal CR*P brought on by others, combined with natural disasters that have upended my life, my job, my home, my everything, and now 'Rona has me locked in with a life-long family abuser) have pushed me to respond to posts on this site in ways that I don't necessarily regret (including leaving for a year or more), but wouldn't choose if I were "calmer".
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Old 01-27-2021, 02:25 PM   #60
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Claimed the brakes failed. Thankfully no one was seriously injured. Was a heck of a ride for the owner/driver coming down Sylvan hill, 6%, and have to make the decisions he made.
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