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Old 01-22-2011, 07:01 AM   #1
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Re: air brake failure

yes

And thankfully so. After all, anyone behind a vehicle needs to maintain a safe distance should the vehicle ahead slow dramatically. Whether it is to keep from running over a child, a brake failure, or a sudden need for McDonalds.
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Old 01-22-2011, 07:29 AM   #2
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Re: air brake failure

I'm no pro on these brakes, never even used one. I do ride the city buses and the drivers tell me that their air brakes send off alarms like crazy and you've 15 seconds to move over to side of road before the brakes do their thing. It's slow braking not on a dime thing. Can't imagine going 50 miles an hour and it stopping on a dime.
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Old 01-22-2011, 07:49 AM   #3
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Re: air brake failure

But it doesn't happen like in the movies. I drive a 33000# single rear axle/with air brakes/mdt everyday for work. Out of curiosity, I have pulled the parking brake valves while traveling say 20-25 mph to see what happens. No skidding has ever occured on dry pavement. Its just like laying on the brakes pretty hard, and coming to a quick stop. Never thought I was going to fly out the windshield. Theres alot of weight that pushes through the brakes. I live in a little bit of rural Iowa, so no other vechicles were around.
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Old 01-22-2011, 08:59 AM   #4
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Re: air brake failure

I pop my brakes often for instruction and entertainment. There is a proportioning valve that disallows to much air being released from the diaphragms at one time when popped and none added.
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Old 01-22-2011, 09:01 AM   #5
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Re: air brake failure

You would have to loose ALL of the air all at once for that to happen. Most air systems maintain 100 to 120 psi. There should be both a warning light and a buzzer at about 60 psi. In my experience the brakes start gradually applying at 50, much below that. I have maintained enough air pressure to keep going with some pretty major air leaks, traffic is the BIG air user, when you step on the brake you dump air.
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Old 01-25-2011, 10:21 AM   #6
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Re: air brake failure

Federal law required the 121Brake System, more commonly known as the Dual Air System on all buses built after 1977, so that is most likely what most of you have. The Brown Crown has this type of system. It is designed to always afford rear braking capability. If it has a failure in the front half of the system, the front brakes will not work. You will get a warning light and buzzer at not less than 60 psi as has been mentioned, but the spring brake is not going to set because the shuttle valve will shut off the leaking front system and you can still stop with the rear brakes by simply pushing down on the brake pedal. The rear tanks will keep the spring brake from applying.

If the the rear system fails, the front brakes and the rear brakes will still work because there is a Spring Brake Modulating valve that releases modulated pressure when you push down on the brake pedal from the spring brake chamber, and the spring brake is held off from applying by the still working front system.

Except in a Total Failure, you can always stop these buses by using the brake pedal and therefore, you have better control to pull over and decide what to do about the problem.

I have pulled the spring brake on my Crown at 55 mph and like others said, it is not like in the movies. No skids and it takes about 250 to 300 ft to stop.
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Old 01-26-2011, 09:43 AM   #7
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Re: air brake failure

Great info, makes me feel better about air brakes Thanks
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Old 01-26-2011, 11:02 AM   #8
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Re: air brake failure

Your welcome, glad I could help.
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Old 02-14-2011, 06:10 PM   #9
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Re: air brake failure

I wanted to move the bus for Halloween last year, so I fired it up, and headed on down the road. Didn't check the brakes.
When I got to the end of the road, guess what happened. Yup, nothing. Pedal hard as a rock, no braking. I was too busy steering hard right into a busy intersection and trying not to hit the cars that were there, with tires smoking to reach for the parking brake.
Let me tell you, when you hit the frame of your bus on the ground at 20mph, it sends quite a shock to your dishes, pans, pots, drawers, and all kinds of stuff you never thought about before. I was pretty lucky, people made room, but not gladly.
I limped it home at about 5mph the next day, from only half a mile away.
I still haven't fixed it, got laid off, too much snow, etc. I need to figure out what happened pretty soon though.
I think it's air assisted hydraulic, and air assisted steering, because it was pretty difficult steering too.

I am hoping I can fix it myself.
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Old 02-14-2011, 07:05 PM   #10
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Re: air brake failure

I didnt originally post this thread.
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