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Old 10-22-2018, 11:29 AM   #1
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Air Break Failure

Hi All,


I have a 2005 Gillig City Bus. The Air Breaks are working great when the bus is running, but as soon as the engine is cut off, the bus begins rolling. My order of operations is, shifting the bus into neutral, pulling the break up, and shutting the engine off. I have also tried pumping the breaks down, it does not change.



Is anyone familiar with what kind of problem this would be? Have they experienced anything similar? I am assuming mechanical but I also could have something in the way I am operating that is causing this problem. Thanks for any insights.
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Old 10-22-2018, 12:23 PM   #2
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That doesn't sound right.

What do your air pressures say? As long as you have pressure, the brakes should operate with or without the engine running or even the key on.

What lever are you pulling? If it's a lever on the floor, that would likely be a cable operated park brake, something that isn't common with air brakes. Most vehicles equipped with air brakes will have a spring brake chamber that is disengaged by air pressure.

Are you sure you have air brakes?
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Old 10-22-2018, 01:19 PM   #3
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Originally Posted by Booyah45828 View Post
That doesn't sound right.

What do your air pressures say? As long as you have pressure, the brakes should operate with or without the engine running or even the key on.

What lever are you pulling? If it's a lever on the floor, that would likely be a cable operated park brake, something that isn't common with air brakes. Most vehicles equipped with air brakes will have a spring brake chamber that is disengaged by air pressure.

Are you sure you have air brakes?
Thank you for the reply. I do have normal pressure on the gauge when I'm trying this. I am pulling a yellow knob that says "pull to apply, parking break, push to release" to the left of me on the drivers dash, nothing on the floor.



(like this.)
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Old 10-22-2018, 01:59 PM   #4
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Well, that is the parking brake knob aka the spring brakes. Pulling on that should apply the spring brakes and the bus should no longer move, running or not. Pushing the knob supplies air pressure to the spring brakes counteracting the force of the spring.

So let me get this straight.

With the engine off, and your foot pushing on the brake pedal, the bus still moves?

Like I said, the engine running or not shouldn't affect the brakes as long as you have air pressure. And without air pressure, that knob should automatically come out, applying the spring brakes.
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Old 10-22-2018, 02:30 PM   #5
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Originally Posted by Booyah45828 View Post
Well, that is the parking brake knob aka the spring brakes. Pulling on that should apply the spring brakes and the bus should no longer move, running or not. Pushing the knob supplies air pressure to the spring brakes counteracting the force of the spring.

So let me get this straight.

With the engine off, and your foot pushing on the brake pedal, the bus still moves?

Like I said, the engine running or not shouldn't affect the brakes as long as you have air pressure. And without air pressure, that knob should automatically come out, applying the spring brakes.
Thank you. To clarify, with the engine off and the parking break on, the bus rolls, unless I have my foot on the floor brakes. So when I walk away to try and park the bus, it goes rolling.

With the engine on and the parking break on, the bus does not roll, whether my foot is on the floor brakes or not. So it is capable of working, it just refuses to when the engine is off.
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Old 10-22-2018, 02:31 PM   #6
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It sounds like your rear brakes are out of adjustment, and the springs can't throw the brake shoes far enough to effectively meet the drums.

That would mean you need to check and adjust the slack, though I assume your bus has automatic slack adjusters. Your brake linings and/or drums might have excessive wear. That would mean a brake job.

What you need is someone who knows how to inspect (and adjust) air brakes look at your bus.

Block your wheels if you are going to crawl under your bus and look.
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Old 10-22-2018, 02:34 PM   #7
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was your bus ever towed perhaps to the lot where you got it? it sure sounds like the rear brakes are Caged.. (as others have mentioned, the spring brakes should apply when the air tanks go empty or when you pull the parking brake lever..



if you pump your brakes dry and the bus still rolls then likely the rears are Caged..

caging is a method to releasde the rear brakes when no air can be pumped in.. ie during towing.. there are bolts which are screwed into the center of each air cylinder that force the spring brakes into release.. if the caging bolts were left in, the result would be no parking brake and no auto brakes if the pressure is drained to 0/
-Christopher
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Old 10-22-2018, 03:39 PM   #8
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If the knob is pulled out, the spring brakes should be applied.

You need to find a mechanic that understands air brakes and can do troubleshooting. What you're describing makes no sense.
The engine being off shouldn't affect your parking brakes.

If the brakes were caged or so far out of adjustment to cause the issue they wouldn't work regardless if the engine was running or off.

You have something odd happening that I've never seen before.
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Old 10-22-2018, 05:58 PM   #9
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Quote:
Originally Posted by Booyah45828 View Post
If the knob is pulled out, the spring brakes should be applied.

You need to find a mechanic that understands air brakes and can do troubleshooting. What you're describing makes no sense.
The engine being off shouldn't affect your parking brakes.

If the brakes were caged or so far out of adjustment to cause the issue they wouldn't work regardless if the engine was running or off.

You have something odd happening that I've never seen before.

his front brakes would work as normal even if the rear were caged.. and driving short distances in an unloaded bus the OP may not even notice the lack of rear brakes...
-Christopher
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Old 10-22-2018, 06:28 PM   #10
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Either the rear brake chambers are caged or the internal springs are broken. I have seen this many times. One spring breaks and the other still holds the vehicle. When the other one goes, then no parking brake.
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