spring brake failure

bevans6 · October 22, 2014, 05:59:34 AM

Article in our local paper today about a tour bus that almost had a brake fire. A trucker following the bus noticed smoke coming from the left drive wheel, pulled out to pass the bus and the drum was glowing red, got the bus pulled over and put a couple of fire extinguishers into the left drive brake while the driver got the passengers out. What probably happened is the spring brake on that side activated or started to activate while the bus was driving, and the engine torque was enough to keep the wheel rolling. Kind of interesting, I would suspect a leaking diaphragm. I know spring brakes can lock a set of duals on an unloaded trailer, and maybe on a loaded trailer, so road friction isn't enough to keep the wheels spinning, but I wonder if the torque and power of a modern engine can overcome a spring brake?

Oh, and a following tractor trailer rear ended a pickup truck that stopped behind the whole mess... No one was hurt and the bus didn't burn down.

Brian

eagle19952 · October 22, 2014, 06:03:39 AM

my first thought would be a spring brake applied to an improperly adjusted shoe...

brmax · October 22, 2014, 06:28:40 AM

Glad no one was hurt, Guys on the brake issue I have noticed in the past after applications if some springs are broke they get cocked some and release very slow and or not fully.
This has not been noticed on regular pre-checks or even could on the standard check along with yearly for that matter, most of the complaints are stated it pulls.
This situation I was taught to look at the opposite wheel for seal leakage and not able to do its job properly( just a step ) then move to other areas and components with testing. I agree weight and power can push the vehicle a pretty good distance. thanks great post
Good day

luvrbus · October 22, 2014, 07:38:54 AM

I never install the spring brake to depend on the chamber to hold enough air to keep it from applying I always plumb one to have a continuous air supply when released then if you have a leaking diaphragm it's no problem till you get it repaired, Brian the new engines can over power spring brakes any good driver should be able to feel the difference IMO

bevans6 · October 22, 2014, 09:44:41 AM

We have very few what you would call professional bus drivers up here. Mostly they seem to be semi truck drivers who got too old to run the long haul, particularly on the tour bus/shuttle bus circuit.

Eagle, how do you have one shoe not adjusted right on an air brake? On mine the only adjustment is the slack adjuster and it adjusts both shoes. Just wanting to learn more...

Up here commercial buses get an over-the-pit documented inspection every 30 days or 12K kilometers. They said improper maintenance didn't seem to be a factor, which I have no idea how they would know that so soon.

Brian

eagle19952 · October 22, 2014, 11:10:10 AM

well i meant both shoes, one set...just one axle...the one that turned red. improperly adjusted would not hold on a hill....loaded...right ?
two axles..no way.

bevans6 · October 22, 2014, 11:24:34 AM

Thanks, Donald, I wasn't sure that I wasn't missing some trick. I pay a lot of attention to knowing about brakes.

Brian

Lee Bradley · October 22, 2014, 12:21:45 PM

Guess it could be a spring brake but I'm more inclined to look for broken return springs or seized anchor pin.

brmax · October 22, 2014, 12:59:44 PM

I believe when the springs are compressed to be able to move the vehicle they are by design a single system aren't they. Pretty sure they leak off together also, now ive had bushes and cedars and even chunks of ice in the way at times what a pain. Other more normal things I recall are the dry s-cam bushings and even dry slack adjusters and as mentioned pins or some broken springs especially if on the lower front side that would seem to hang and cause a drag problem and not really drag a lot in a situation to feel a pull probably get hot though. So im still stuck on the big park spring broke and cocked preventing the rear diaphragm carrier to full return as it should.

sparkplug188 · October 22, 2014, 01:00:04 PM

Michelin has a three part video series on wheel end safety. It is definitely worth watching if you own a bus.

https://www.youtube.com/watch?v=wrsj2UoMeys

https://www.youtube.com/watch?v=n1sZ5OAcaFc

https://www.youtube.com/watch?v=ETOAVzB2cOw

krcevs · October 23, 2014, 04:08:11 PM

Quote from: bevans6 on October 22, 2014, 09:44:41 AM
We have very few what you would call professional bus drivers up here. Mostly they seem to be semi truck drivers who got too old to run the long haul, particularly on the tour bus/shuttle bus circuit.

Eagle, how do you have one shoe not adjusted right on an air brake? On mine the only adjustment is the slack adjuster and it adjusts both shoes. Just wanting to learn more...

Up here commercial buses get an over-the-pit documented inspection every 30 days or 12K kilometers. They said improper maintenance didn't seem to be a factor, which I have no idea how they would know that so soon.

Brian

Brian,
about the only way you can have just one of the brake shoes adjusted and the other not adjusted properly is if the axle is running wedge brakes. Instead of a slack adjuster you have an air brake chamber activating a wedge between the shoe rollers.

Ken

Jim Eh. · October 23, 2014, 05:51:15 PM

Quote from: bevans6 on October 22, 2014, 05:59:34 AM
Article in our local paper today about a tour bus that almost had a brake fire. A trucker following the bus noticed smoke coming from the left drive wheel, pulled out to pass the bus and the drum was glowing red, got the bus pulled over and put a couple of fire extinguishers into the left drive brake while the driver got the passengers out. What probably happened is the spring brake on that side activated or started to activate while the bus was driving, and the engine torque was enough to keep the wheel rolling. Kind of interesting, I would suspect a leaking diaphragm. I know spring brakes can lock a set of duals on an unloaded trailer, and maybe on a loaded trailer, so road friction isn't enough to keep the wheels spinning, but I wonder if the torque and power of a modern engine can overcome a spring brake?

Oh, and a following tractor trailer rear ended a pickup truck that stopped behind the whole mess... No one was hurt and the bus didn't burn down.

Brian

This technically would not be a spring brake failure but rather an air system failure. If it were a spring brake failure it would have a reduced stopping force when applied?

bevans6 · October 24, 2014, 04:21:02 AM

It was just an interesting situation that might have possibly been caused by a single spring brake applying while the bus was under way on a highway. Not all that sure what to call it, or what actually happened to the bus, but quite interested in the discussion of how it might have happened on a single drive wheel, so it was a good thread from my curiosity's point of view!

I am always very curious about brakes and what they can do when they screw up.

Brian

belfert · October 24, 2014, 07:09:19 AM

I had a tag axle brake lock up in 2011. Luckily, we got stopped before it became a fire. Smoke was pouring out when we stopped. The cause was a brake chamber that wasn't retracting all the way. The frustrating thing is I had paid a shop to check over my brakes just the day before. They had replaced a front brake chamber.

lostagain · October 24, 2014, 07:51:42 AM

Last time I had my dump truck in for inspection 3 month ago, (in BC), they said now they have to look at all the springs in the brake cans, looking for broken ones. They take the rubber plugs off. I guess DOT said it is a problem worth addressing.

JC

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