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Old 12-12-2016, 04:01 PM   #1
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Question Brakes were frozen. Not now question

Started bus the other day when it was 15' above. Started right up and the brake light came on. Frozen. Waited until to day and abouut 35 deg.Opened the drains on 2 tanks and go nearly nothing as to moisture. Removed no.1 supply line and dumped 2 cap fulls of Air brake antifreeze into it. At same time i cleaned and thread taped the brass fitting coming off the compressor.
Started bus and red light still on 10 minutes later. 20 minutes or so red light still on but brakes are free.
What should i have done?
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Old 12-12-2016, 05:33 PM   #2
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Originally Posted by Versatile View Post
Started bus the other day when it was 15' above. Started right up and the brake light came on. Frozen. Waited until to day and abouut 35 deg.Opened the drains on 2 tanks and go nearly nothing as to moisture. Removed no.1 supply line and dumped 2 cap fulls of Air brake antifreeze into it. At same time i cleaned and thread taped the brass fitting coming off the compressor.
Started bus and red light still on 10 minutes later. 20 minutes or so red light still on but brakes are free.
What should i have done?
Well, I'd say you should have done a little more troubleshooting. Some brake systems *REALLY* do not like the air-brake antifreeze; something about mucking up the valves in the rear (or trailer) brake control modules.

My *FIRST* question would have been, do you actually have air pressure in one tank or both? Never mind what the gauge says ... because the sensors can fail or freeze, giving you a false reading. My last Volvo would do this on the secondary tank when it was under 32 degrees ... and would continue giving a false reading until the truck was turned off and restarted (we never diagnosed why it did this, as it was much easier to simply do a reset, for no more than it occurred).

Second, once you've established there is no air pressure ... and you've given the system some time to build up ... some (many?) air systems take longer when cold to build up pressure. It should have reached enough to turn off the red light in under 10 minutes. There's a chance of moisture being in the system, or more likely, something sticks in really cold weather.

What is (was) your air pressure showing? Often brakes will release between 40-60 PSI, which is under the threshold for the warning light. Are (were) you losing air pressure? Any audible leaks?

Air tanks should be drained on a regular basis - at least at the end of every day of driving. For a bus on an active school route, this would be 5 days a week. For us, maybe much less often, but that makes it all the more important to be done. How much moisture do you get the first time you drain the tanks? (I think you said minimal-to-none.) How much on a daily basis?

I realize it was really cold, and to be honest, I wouldn't have wanted to mess with it at that time either. Often air brake systems have issues when it's "not cold", which are really only much more evident when temperatures drop below freezing.
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Old 12-12-2016, 06:38 PM   #3
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Ball peen hammer to the brakes? It happened a few times in winter to the Preventive Maintenance Teams' 40' trailers when I was a USAF sky-cop consigned to the frozen wasteland that was the Grand Forks AFB missile field.
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Old 12-13-2016, 08:44 AM   #4
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Thanks i am learning. I have about 4 tanks under there and looks like they al have drains. I only opened the 2 lower ones. I agree that sometimes the cold only shows you the problem already there. I only fired it up to move it from where i was parking to get a vehicle behind it.
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Old 12-13-2016, 10:44 AM   #5
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sometimes the air dryer is the culprit.. in fact on MOST of the international busses ive seen the air-brake warning light to the dash sensor is actually up at the governor.. if the governor kicks the compressor in but the air dryer has not gone into a normal OP state then you wont build pressure...

MOST of the international dog-nose anyway have Mechanical pressure gauges.. theres no sensor.. just an orange and green nylon line going up to the gauge from the 1 and 2 tanks.

if you have an AD-4 or AD-9 air dryer, it has a heater in the bottom of it.. if you shut your bus off wit ha full tank of air (as most people do) .. the unpurged moisture from the last purge cycle will freeze in the bottom of the air dryer where some of the check valves are because that heater is no longer on..

sometimes if you start the engine and simply give it 15-20 minutes to warm up, that heater will unfreeze and you'll build pressure normally.

if you know its going to be bitterly cold, run your bus, wait for the purge SHHHH!! from the dryer, shut the bus off, and drain all 3 tanks at this time... so it is parked with drained tanks...

you may still have to let the air dryer warm up a bit, but you have better chance of it working right sooner..

another thing is it is Possible that the unloader valves in your compressor froze and stuck open as well if there was any moisture at the head.. if the air inlet filter to your compressor has ever been removed for al ong period of time or you dont have one installed, there can be a bit of grime on the unloader valves.. the bus is turned off wit hthe compressor unloaded (full tanks of air).. and its possible they froze open.. and again usually once warmed up they will free.. if your air-pressire Alarm sensor is on the governor, you'll know right away that the unloaders are open as this alarm will sound even if the tanks are showing above 90 PSI.. as the test-line for the governor goes way below because of the open unloaders when the air dryer clears...

-Christopher
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