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Air brake trouble with older L 9000 Ford.
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proud2Bafarmer
Posted 7/28/2014 07:14 (#3989603)
Subject: Air brake trouble with older L 9000 Ford.


Baldwin City, KS
We have a '72 Ford L 9000 that we pull a trailer with. It started out by way over pressurizing the system and not kicking out. Put a gov on compressor and partially solved the issue. Right tank pressures up and levels off normal. Left one won't pressure up at all. I've determined that it gets supply from the right tank which appears to handle trailer supply. I cleaned up the little bypass valves and made sure air is flowing to left tank. Still can't get it to pressure up past 55#. I've aired that tank up manually with poor results as well. It seems the air is leaving that tank as it's put in. I can hear air moving in the system, but find no external leaks. Seeing as how the tanks appeared to be tied together, I'm at a loss as to how one holds good pressure, but the other won't pressurize. I'm assuming problem is downstream from left tank, but I'm not knowledgable enough on air brakes to diagnose further. Any thoughts? Thanks.
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Thud
Posted 7/28/2014 07:45 (#3989656 - in reply to #3989603)
Subject: RE: Air brake trouble with older L 9000 Ford.


Near-north Ontario, French River
Hold your hand under the exhaust port of the air dryer. If the exhaust valve is stuck open it's difficult to hear the leak when pressure is relatively low.
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proud2Bafarmer
Posted 7/28/2014 08:13 (#3989702 - in reply to #3989656)
Subject: RE: Air brake trouble with older L 9000 Ford.


Baldwin City, KS

No dryer on mine
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towman2000
Posted 7/28/2014 08:24 (#3989722 - in reply to #3989603)
Subject: RE: Air brake trouble with older L 9000 Ford.


SouthCentral WI
The way it is suppose to work is, you have the compressor feeding the dryer (if you have one) to the wet tank and then 2 feeds out. 1 to the primary, 1 to the secondary. both of these lines have check valves in them. It is strange that one is building up all the way in one tank and the other isn't. An air leak will usually make both tanks remain the same pressure WHEN THEY ARE BUILDING AIR. Unless you are confusing the wet and secondary. Sometimes these two tanks (wet and Primary)are in the same tank with a bulkhead weld in the middle of the tank.
If it had an air dryer, did you hook up the sensor and dryer control line in the right order on the governer? Sensor line goes on the end, Air dryer middle, vent port is next to adjuster end. Worst comes to worst take the supply line (large line) off at the compressor an hook shop air to it. It will make diagnoses much simpler.
http://totaltruckparts.net/brake/airschematics.html
This isn't the diagram I wanted, but it shows what I mean.
Towman
Edit: I see you don't have an air dryer, so the center port on the compressor (small line) gets plugged. Are the pressure reading from the gauges on the dash when you are building air, parking brakes set. You may have an air leak? fan clutch? brake valves above drive axle? air ride? Maybe a pressure relief valve on one tank, since you said you were over pressurizing the system, maybe a rotted air tank (it is a 71). An air leak isn't the first thing I would look for if it doesn't BUILD air correctly. Again hooking an outside air source to the supply line will make the job much easier.



Edited by towman2000 7/28/2014 08:46




(Air brake Diagram.jpg)



Attachments
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Attachments Air brake Diagram.jpg (61KB - 531 downloads)
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Thud
Posted 7/28/2014 08:48 (#3989763 - in reply to #3989722)
Subject: RE: Air brake trouble with older L 9000 Ford.


Near-north Ontario, French River
My bad towman, you are correct that the dryer should come before the tanks. Unlikely but how about air ride suspension with a blown bag. Air isn't generally sent to suspension(and other accessories ) unless system pressure is greater than 60ish psi. If secondary tank isn't going above 55ish I'd be looking to suspension or other accessories ( cab suspension, pto controls, pointless hook if equipped, even air power wipers etc). If the leak can't be easily heard it must be a large leak ,ie blown bag or severed/disconnected line.
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Browtrucking
Posted 7/28/2014 09:19 (#3989809 - in reply to #3989603)
Subject: RE: Air brake trouble with older L 9000 Ford.


halfway between Lapeer and Port Huron, MI
Is the gauge accurate? If it builds to 55 it should go the rest of the way if the wet tank is fully pressurized unless you have check valve issues but once they open at all they should stay open. Being that old there shouldn't be a lot of extras, pull the drain and screw in a gauge back track from there.
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RodInNS
Posted 7/28/2014 11:00 (#3989933 - in reply to #3989603)
Subject: RE: Air brake trouble with older L 9000 Ford.


I would say you have a leak somewhere on the secondary that you can not hear over the engine... it happens. Like mabey a big bloody hole in the tank and that won't even hiss when it leaks. Been there, done that...
You should have a dryer, wet, primary and secondary and the wet and primary are probably bulkheaded in one tank. Also keep in mind that just about anything could have been changed on an old truck at this point...

Rod
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dave morgan
Posted 7/28/2014 12:08 (#3989991 - in reply to #3989933)
Subject: RE: Air brake trouble with older L 9000 Ford.


Somerville, Indiana
we have an old IH truck that came from a gov't air port = always built up air to less than required for safe service of the brakes...a check valve was put in backwards = probably the valve was faulty because a good valve would stop the air completely?..Turned it around so the very hard to see arrow pointed in the direction of correct air travel and all was fine...Seems the older the truck the more chances a squirrel mechanic was involved in messing more things up to where service was totally unacceptable...I plumb into the first air tank with shop air regulated to a hundred pounds to service the system = easy to find the right size and type thread and no damage to other components.
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MW farms
Posted 7/28/2014 18:50 (#3990455 - in reply to #3989991)
Subject: RE: Air brake trouble with older L 9000 Ford.


Doesn't have to have a dryer on it. Might have moisture ejection valve of some sort. Could be a combination of thing going bad causing it to not build air. Bad valve plugged air line or bad brake pot. If you can hook it up to shop air and listen with truck shut off it makes finding it a lot easier. Most air valves open around 55 psi so that makes me think something is leaking
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proud2Bafarmer
Posted 7/28/2014 22:11 (#3990950 - in reply to #3990455)
Subject: RE: Air brake trouble with older L 9000 Ford.


Baldwin City, KS
Thanks guys. That was all very helpful.
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