AIR BRAKES

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AIR BRAKES

Home > Discussion Forum > Mechanic's Corner - Brakes

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All Messages in Thread	Author	Date
AIR BRAKES	KEN	6-16-02
I OWN A 1980 CHEVROLET 60 SCHOOL BUS WITH AIR BRAKES. THE PROBLEM IS THIS. THE SYSTEM WILL NOT HOLD AIR PRESSURE FOR VERY LONG. THE SYSTEM WILL CHARGE WITH AIR AND THE GOVERNOR WILL KICK IN AT AROUND 120 PSI. BUT AFTER SHUTTING THE ENGINE OFF FOR ABOUT 1-2 HOURS, THE SYSTEM WILL BE BACK BELOW 60 AND I HAVE TO WAIT TO GET RECHARGED BEFORE THE BUS WILL MOVE. I DO NOT SEEM TO HEAR ANY HISSING, LEAKING SOUNDS, BUT I DO BELIEVE IT MUST BE LEAKING. OTHER BUS OWNERS SAY, ITS JUST ONE OF THOSE THINGS AND NOT TO BE WORRIED. HOW LONG IS AIR PRESSURE SUPPOSED TO HOLD, HOURS OR DAYS OR WHAT? I DON'T WANT TO BE STUCK SOMEWHERE AND NOT BE ABLE TO MOVE DUE TO INADEQUATE AIR PRESSURE. WHAT IS THE MOST COMMON THING TO GO WRONG? OR IF THIS IS NOT TO BE REPAIRED BY THE AVERAGE PERSON,ONLY PROFESSIONALS,WHERE IS A GOOD PLACE TO GET IT REPAIRED WITHOUT BEING RIPPED OFF. I AM IN THE TAMPA, ST. PETE AREA OF FLORIDA. ANY HELP WOULD BE APPRECIATED.
Re: AIR BRAKES	Francis Hayes	11-11-04
This is a long shot,happens once in a great while.Due to the age of the equipment,check straps holding air tanks.I have found over the years that as a vehicle ages,tanks rust out in the most interesting spots,hence my thought of under the rubber strips that are under the tank straps.Loosen the straps a smidge,move or reposition the tanks just enough to get soapy water,or( what I use is leak detector liquid)on area that is concealed,there might be a good enough leak for an air drop,but you can't here because its under the rubber's under the mounting straps. good luck
Re: AIR BRAKES	Joe	7-22-02
If it were mine, I wouldn't bother trying to find the leak or leaks. But There may be a few places to start that are easy. First if your bus is like the ones we work on, it has two tanks and two indicater needles in the one air pressure indicater. If it does and both are going down it is after the second tank, as there are two check valves in the system. One is between the compressor and the first tank and the other is between the first and second tank. If both are going down, check everything after the second tank. If not Start by removing the large line from the compressor and hold your finger over the line to see if it is "Bleeding" back. The next thing to check is the dash valve that releases the spring brakes. If it has air windshield wipers, check that valve. Next check the foot valve followed by the relay valve in the rear for the rear brakes. Like any other problem, start at the beginning (compressor) and work your way back.
Re: AIR BRAKES	Sam Watson	6-17-02
The standard is 2PSI or less per minute of pressure loss on a charged system and engine off. As you can see, a 60 PSI loss in 1 hr only amounts to 1 PSI per minute, only half of the allowed maximum. Enjoy your unit, sounds like your system is OK
Re: AIR BRAKES	larry moore	6-17-02
Ken in reguards to your air pressure drop, 60 lbs is not acceptable, charge up your bus take a bottle of water and add some dishsoap and spray all your air valves and your fittings,dontforget your brakepots also someware you are losing your air.I have work for many years as a mechanic and we have some trucks that donot lose any air to speak of others lose some i do feel yours is not normal, hope i have not confuse you to much,take your time and you can find the the leak your self then maybe then get someone to repair or replace the part. please keep us inform larry
Re: AIR BRAKES	Sam Watson	6-18-02
Larry, while it's true that some vehicles leak down a lot less, Ken's brakes are well within the NHTSA pre-trip inspection sheet for air brake equipped vehicles. The 2 PSI leakage per minute is really very little when you consider how much of the system is constantly under pressure. As an old,(in both meanings),fleet mechanic where we had to do complete brake checks every 90 days, let me tell you that you can spend a lot of time looking for every little "fuzzer" in the system. If the NHTSA is happy with 2 PSI per minute, then don't sweat the small stuff.
Re: AIR BRAKES	Mark O.	6-24-02
I have worked in fleets where several vehicles were puchased at the same time. Among those, even though they were brand new, some held air for days and days and others were below 60 PSI between morning and afternoon runs. Given enough time and effort every little leak can be found but in most cases, unless it is more than the 2 PSI per minute, it most likely isn't worth your time and effort to try and find the leaks. Mark O.
Re: AIR BRAKES	NAPA dude	7-16-02
You are within limits with this small bleedoff. However, if you want to try to track it down, the soapy water in a squirt bottle is the ticket. Start at the brake actuators and any plastic lines.