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Author Topic: Air Dryer Question  (Read 856 times)
JackConrad
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73' MC-8 8V71/HT740 Southwest Florida


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« on: September 20, 2011, 09:49:38 AM »

   When we moved the bus to install the new steering, the air system would not fill up. Long story short, I found the air dryer discharge valve stuck open.  I removed the valve, cleaned it and re-installed it. Everything worked OK.
   Sunday, we started the bus to move it back where we had it parked before installing the new steering. Same problem, system would not air up. Air dryer discharge was leaking. I disconnected the small air line that is attached near the bottom of the air dryer and the leak stopped. I could feel a slight leak from the air dryer fitting that I disconnected the hose from. When I put my finger over this leak, it would cause the discharge valve to vent.  With this line disconnected, bus airs up with the slight leak from the fitting (and dryer does not "vent when comnpressor kicks out). My air schematic drawing is very poor quality and I cannot trace down this small "trigger" airline.  Anyone know where this air line connects into the system?  Thanks, Jack
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« Reply #1 on: September 20, 2011, 10:02:41 AM »

It connects to the center fitting on the air governor.  That is  the port that controls the unloader valves inside the compressor, so that it stops delivering air when it reaches cut-out pressure, and the line up to the air dryer tells the air dryer to purge while the air compressor is not delivering air.  When the governor senses that cut in pressure has been reached, it switches, the compressor starts to deliver air and the purge valve on the air dryer closes.  At least that is how it works on my bus.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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gumpy
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« Reply #2 on: September 20, 2011, 07:24:10 PM »

Jack,

Sounds like your governor is sticking. Take it apart, clean, lubricate, and replace o-rings (or put a new one on for about $20).  

I had this same problem (same symptoms) several years ago. I put a new governor on, then cleaned the old one and lubricated it. I put it back on, and put the new one
in the spare parts bin. It's still there.

When I was having the problem, I found that I could tap the governor with the handle of a long screwdriver and it would free up and fill the air system.  If I remember
correctly, I was having the problem primarily when it was cold.

craig
« Last Edit: September 20, 2011, 07:27:28 PM by gumpy » Logged

Craig Shepard
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