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Author Topic: Runaway bus?  (Read 1384 times)
windtrader
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« on: November 02, 2017, 10:08:07 AM »

An interesting incident yesterday got me wondering if anyone's heard of a bus losing traction while parked with brakes set?

The neighbor was getting a load of wood delivered. The 3 axle truck was backed up a fairly steep asphalted slope. After unloading about half the load, the truck decided to take off down the slope and into the property across the street. Fortunately, the truck stopped before ramming the house and just some shrubs got roughed up.

How this happened got me wondering if it can happen on a bus. The truck tag was down to help carry the load. As the weight came off, the tag stayed down while the drive axle started unweighting. That allowed the truck to lose traction and set it down the hill.

Is there anyway a 3 axle bus could somehow lose traction on the drives, is there any precaution one should take when parking a coach?
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Don F
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« Reply #1 on: November 02, 2017, 10:23:26 AM »

Were the truck's drive tires locked up and sliding or were the brakes out of adjustment so the spring brakes were not holding?

In reference to coaches:  The drive axle DD3's on older MCI's are notorious for not holding well when the coach is liable to roll backward (with park brake applied).  One should carry a wheel chock and use it if parking pointing up hill on grades.  Even if brakes are adjusted properly.  This was SOP when we operated MC8's and 9's.
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« Reply #2 on: November 02, 2017, 10:54:17 AM »

Anything can happen with a load on a slippery incline.  I've seen a single axle loaded farm truck slide down a driveway minutes after backing up that same driveway.  Once traction breaks the sliding resistance is less than the static resistance so the unit keeps sliding. In other words, the unit can sit there for a long time but once it starts sliding its not going to stop until it gets to the bottom of the incline or until something else intervenes to stop it.  In the case I'm referring to only one side broke traction so the wheels (duals) on that side actually rotated backwards as the truck slid down the incline.  Buses can't defy physics - they're big heavy pieces of machinery and gravity always wins eventually.
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R.J.(Bob) Evans
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« Reply #3 on: November 02, 2017, 10:59:40 AM »

If the coefficient of friction between the tire and the asphalt is low enough, the weight of the truck can easily overcome the force required to start moving(sliding).  Heat from the tires, oily residue on the asphalt, moisture on tires, angle of the slope, weight of the truck on each axle are all factors.  

I have "slid" off a 2 degree slope on a 4 wd  backhoe with all brakes locked!  The ground was damp clay.  I had to turn around and drop the hoe to stop.  Even putting the bucket down didn't stop me!  It was scary!

The precaution is to use "chocks", and when that fails ---run fast in the opposite direction  Grin

Steve
 
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Steve Toomey
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« Reply #4 on: November 02, 2017, 11:23:16 AM »

I worry about this also, as the Scenic has the ability to unload the tag axle which is where the spring brakes are located. So if the brake is set and the tags are unloaded on a slippery surface it could get interesting. I however always chalk and axle to be safe automatically while I park though.

Safe travels.

Jack
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eagle19952
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« Reply #5 on: November 02, 2017, 11:38:22 AM »

An interesting incident yesterday got me wondering if anyone's heard of a bus losing traction while parked with brakes set?



Is there anyway a 3 axle bus could somehow lose traction on the drives, is there any precaution one should take when parking a coach?

yes. adjust your own brakes. trust no one to do it for you.
the plaintiffs attorney will eat you alive.
blaming the mechanic doesn't work there.
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Donald PH
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« Reply #6 on: November 02, 2017, 12:45:15 PM »

When I was a young truck driver I had a Peterbuilt come back from the shop with new brake shoes and linings.  When coming down a long hill some white smoke came out of the brakes at the wheels as the brakes were applied. What happened is the new linings did not completely "arc" to the old brake drums and the linings were worn down to match the arc of the old drums. After I got to my first stop the brakes were set and the tractor started rolling; the brakes were completely out of adjustment.   The same will happen to an older MCI bus if the brakes are out of adjustment or if air leaks off the brake system. 

This will not happen to newer trucks or buses which have spring brakes or "maxi cans" because the strong springs holds the brake linings against the drums.  On the older buses, wheel chocks are definitely a good idea.
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brmax
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« Reply #7 on: November 02, 2017, 02:31:44 PM »

I dont really understand worn down to match the arc of the old drums.  Roll Eyes
But i prolly dont want to
I stress when adjusting brakes to have the wheel off the ground and able to turn.
Always an interesting subject for sure,

Good day
Floyd

ps: I think it’s a good thing to “see” and understand how your vehicles brakes work.
      Take the covers off any brake access points so to veiw a few brake applications.
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« Reply #8 on: November 02, 2017, 03:23:09 PM »

Speaking of chocking wheels... After doing lots of reading on the subject I found that chocks should be 1/4 the height of the tire to be most effective. That means 10" tall chocks for most of us. Not easy to find, but since my driveway has a decent grade I sprung for two. The 10" chock looks small in the photo, but next to what's usually used these chocks are huge.

Richard
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« Last Edit: November 02, 2017, 04:34:10 PM by richard5933 » Logged

Richard
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« Reply #9 on: November 02, 2017, 04:27:34 PM »

Don't forget a leaking rear oil seal coating the lining.I still prefer synthetic grease and proper seals for the older coaches, at least, but that is another discussion.


Here's some, albeit lower, but they're cheap enough to get four or six? Also check your coach on a fairly steep grade,safely, to see if your parking g brakes are holding. Not a substitute for proper chocks, of course if desired. I have my coach chocked on level floor in shop while rebuilding dd-3's.
« Last Edit: November 02, 2017, 04:38:10 PM by chessie4905 » Logged

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« Reply #10 on: November 02, 2017, 04:30:36 PM »

"what usually gets used"

Is inadequate.

Be very careful following the herd...

What do the big boys with ample capital do?

happy coaching!
buswarrior
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« Reply #11 on: November 02, 2017, 04:35:24 PM »

Weak parking brakes is a devil.

Both spring and DD3 chambers are capable of moving the actuating mechanisms, fooling all watching that something is happening, but they might not "squeeze" according to spec....

Brake dynometers, drive on rollers, are hard to come by in North America...

Test your parking brake, give it pull while rolling along on a quiet side street, see if you like the resulting stop.

Long ago, there was a pair of videos... I did a GM 5307 transit, another busnut did their coach, before and after "adjustments"...

Crumbs, who was it? And where did it get posted?

happy coaching!
buswarrior
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« Reply #12 on: November 02, 2017, 04:50:35 PM »

If the big spring in a "maxi brake" breaks, or part of it, it obviously won't do it's job. Sometimes you can't tell spring is broken. Bus Warrior is right on. Check them at soonest chance, and if you are concerned of going through windshield, as some were concerned on a prior discussion, release them before you come to a complete stop, or right before nose contacts windshield.
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« Reply #13 on: November 02, 2017, 05:54:44 PM »

Just for fun...

The power of the archives of the Boards:

Google "buswarrior parking brake stop"

http://www.busnut.com/bbs/messages/233/18528.html?1187138090

Back when I typed in full and complete sentences....

happy coaching!
buswarrior
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« Reply #14 on: November 02, 2017, 05:57:47 PM »

And from BCM:

http://www.busconversions.com/bbs/index.php?topic=1489.55;wap2

Where is Buffalo SpaceShip???

The site at the end of the link is long gone...

happy coaching!
buswarrior
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RJ
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« Reply #15 on: November 02, 2017, 06:33:13 PM »

Long ago, there was a pair of videos... I did a GM 5307 transit, another busnut did their coach, before and after "adjustments"...

Crumbs, who was it? And where did it get posted?


Buswarrior -

Here's the beginning of the thread you're looking for:

http://www.busconversions.com/bbs/index.php?topic=1489.0;wap2

All the "newbies" who haven't been around since this thread was initially posted should take the time to read the whole thing, all 16 pages, plus the link to the blogspot article that has even more information.

I'll talk to Brian to see if he's still got the video. . . stay tuned.

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #16 on: November 02, 2017, 06:55:53 PM »

FOUND IT!!!

https://www.youtube.com/watch?v=EOx7J2_qetU

Yeah, baby, the power of group memory and Google!!!

From the history, note the follow up:

buswarrior:
A word of caution from later posts.

The video is resident elsewhere, perhaps someone else remembers where?

After the video shoot, from the large difference in results, Brian's brakes were found to be contaminated by way of leaking wheel end seals, thus, its stopping distance was far longer than it should be.

The evidence, as recorded in the video, could be re-packaged to serve as a warning as to what happens to your ability to stop if the wheel end seals are leaking into the brake drums.

He tore down the wheel ends shortly after this thread, discovered this, and fixed it all up.

No matter spring or DD3 systems, when everything is up to snuff, they all stop much the same, with a transit coach having some advantage due to the larger swept area of the brakes installed for the constant stop and go.

So, take your coach out, ensure all is secure, which you should be doing every time it moves anyway, and give it a whirl!



happy coaching!
buswarrior
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« Reply #17 on: November 02, 2017, 09:38:45 PM »

Getting back to Don's original question, is possible for the tag axle to have more air in the bags than the drive axle, thus reducing the traction on the drive axle?  The steering axle and tag axles don't have DD3s or Maxi Cans, do they?  Do any of you have a manual adjustment for the air in tag axle bags?

Mike
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TomC
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« Reply #18 on: November 03, 2017, 09:11:34 AM »

Complete driver error. The driver should have released the lift axle when unloading. You're parking brake should be such that only a bull dozer could slide the bus when applied. Good Luck, TomC
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« Reply #19 on: November 03, 2017, 10:10:46 AM »

The newer buses have the spring parking brake on the tags also now,the dd3 chambers were notorious for not latching tight when the adjustment was off just a little bit
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« Reply #20 on: November 03, 2017, 12:08:50 PM »

RJ - link not working, got an update?
http://http//r4106.blogspot.com/2006/08/intelligent-dumb-question-answered_10.html

I am nearly certain what the driver said indicates a driver error. He should have taken pressure off the tag axle before unloading the wood. People heard squealing so the drives were locked and did not fail. When the truck has some amount of wood taken off, the drives lost just enough traction to get it skidding down the pretty steep driveway. He said he never had that happen before. First time for everything; I'm sure he'll remember in the future. LOL
« Last Edit: November 03, 2017, 12:12:11 PM by windtrader » Logged

Don F
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« Reply #21 on: November 03, 2017, 12:44:40 PM »

I for one can not believe the wood truck driver did not take the most basic safety precautions if he parked that truck on that steep of grade.

Multiple chocks.  Lowest gear in Tranny if manual.  If an automatic then there you have it.  We used heavy safety ROPES tied off to something anchored.

Rope that puppy off.  The driver should be fired.  Then sent back to drivers school.  There is no excuse NOT to conduct basic SAFETY considerations.
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« Reply #22 on: November 03, 2017, 01:46:56 PM »

I for one can not believe the wood truck driver did not take the most basic safety precautions if he parked that truck on that steep of grade.

Multiple chocks.  Lowest gear in Tranny if manual.  If an automatic then there you have it.  We used heavy safety ROPES tied off to something anchored.

Rope that puppy off.  The driver should be fired.  Then sent back to drivers school.  There is no excuse NOT to conduct basic SAFETY considerations.

If the truck was a manual transmission it would have been impossible to off load w/o power take off running so the driver would have to leave running in neutral in order to unload. But he should have unloaded the tag axle prior to setting the brakes.
Grin  BK  Grin
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« Reply #23 on: November 03, 2017, 03:14:04 PM »

In a coach with a 6k rated tag axle, if the tag has enough pressure to unload the drive axle, structural failure of the tag bag mount will be imminent. They can't take that kind of weight.

The newer 45 footers, the tags have become rated pretty much the same as the steer axle, and you know it, when trying to start out in slippery conditions, or the drive tires hit the painted stop line at the intersection as you pull away.

When this hobby goes from single circuit service chambers and a hand brake parking next to a current 2 axle spring brake system, there are a lot of "it all depends"... add in some crazy maintenance, or lack there of....

Not a bad idea to have a proper set of chocks for your coach, and use 'em?

happy coaching!
buswarrior


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« Reply #24 on: November 03, 2017, 04:30:52 PM »

B  K :  if the driver had to engage the power take off to dump that load of firewood, why in the world did he snatch defeat from the jaws of victory and spot his load in such a high grade situation guaranteed to fail... from the get go?

This makes it worse.  Not only should he be fired for being stupid and dangerous but he also should be made liable for any damage his stupidity resulted in.  No excuses.  But then again we are not dealing with reality here.  Only stupidity.

We used to lump, (move) furniture in San Francisco.  The very hilly parts of town then actually had special dedicated cleats intended to tie off heavy trucks soss they did not run out of control down hill.  Common sense.  Long ago.
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RJ
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« Reply #25 on: November 03, 2017, 08:36:42 PM »



Too many http's, Don.  Try this:

http://r4106.blogspot.com/2006/08/intelligent-dumb-question-answered_10.html

FWIW & HTH. . .

 Wink
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RJ Long
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windtrader
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« Reply #26 on: November 04, 2017, 11:32:15 AM »


Thanks Russ,

Great info. Adding to the annual inspection process, one of the busses I looked at was being sold by a Bay Area tour operator who mentioned how thorough the mechanics check out the busses. I believe he said it takes two mechanics the better part of a day to do the inspection.

He said there was no specific charge for the inspection but it is baked into the fees the state gets for licensing commercial vehicles, some goes to to DOT for this inspection.

One thing for certain is in the very unlikely event I buy a currently registered Calif commercial bus for a conversion, I'll surely have the mechanic doing the bus survey to skip all the safety related checks.
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Don F
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« Reply #27 on: November 05, 2017, 07:53:29 AM »

Only a day, for "an inspection" Huh

Long ago and far away...

The annual took 2 mechanics for 5 days to go through an MC8-9-102A. There were lesser levels at other time markers, from daily on up to 6 month.

Pages and pages of company written inspection and preventive maintenance procedures, blending the manufacturers' content with all that stuff that isn't written down. Every moving part was involved, either tested, inspected, lubed, adjusted, whatever...

80 hours of labour annually, 4 hands working together.

Reliability comes from familiarity, inspection, and replacing/adjusting/repairing before failure.

Every busnut needs either a pneumatic or battery powered grease gun... that which is hard to do, won't get done...

How many hours does a busnut spend on pure inspection/preventive maintenance each year?

happy coaching!
buswarrior

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