Author Topic: Air system problem  (Read 9645 times)

Offline gus

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Re: Air system problem
« Reply #15 on: May 16, 2013, 05:07:08 PM »
Bob,

Then 4104 original system operated in the 102-82psi range, or close to that. I'm away from home and can't check my manual, but that is close. It is lower pressure than later systems which are 120psi or more..

It appears that purge valve on the dryer is set to that original pressure.

So, what I'm saying is that the gov is set too high. Reset it to around 105psi and see how that works. The screw adj is under the plastic cap on top of the gov. As i recall it is lowered by turning CW bur I may have it reversed. Turn just a little at a time.

I'm not sure how to adj the gov low point but someone here will. I think maybe it changes when the high press is adj-it has been awhile since I messed with these adjustments. Any local big truck mechanic will know this or you can probably google it.

The bags are independent of the rest of the air system and are supposed to stay up for days, mine never did!

PD4107-152
PD4104-1274
Ash Flat, AR

Online bevans6

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Re: Air system problem
« Reply #16 on: May 17, 2013, 04:06:10 AM »
Thinking about this step by step, I come up with these ideas...

The governor controls the purge valve, so the purge valve isn't set to any pressure on it's own.  The governor has a set range of pressure low to high based on it's internal spring and you can set the high point or the low point by changing the pre-load on the spring, but you can't adjust the range without internal surgery to the unit.  The range is nominally 25 - 30 psi, so you can have 95 - 120, or 85 - 110, that sort of thing.

The governor controls the compressor and tells the purge valve when to open and close.  When the purge valve is closed, air is being produced by the compressor.  If the engine is turned off while the purge valve is closed the air is held in the system by the compressor valves and there is system air pressure inside the air dryer.  If the purge valve is open, it dumps all the air inside it's chamber and in the line between the compressor and the air dryer, and the purge valve stays open until it's told to close again by the governor (or when system air pressure leaks down).  When the purge valve is open air is retained inside the system by the check valve on the air dryer.

With the symptoms you have - air leaks out fast when the purge valve is open, but doesn't leak out fast when the purge valve is closed - I would have another look at the check valve on the air dryer, and the check valve that may be on the dry tank between the wet tank and the dry tank.  They are supposed to be what is keeping air in the system when the purge valve is commanded open.

Brian
1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Allison MT-647
Tatamagouche, Nova Scotia

Offline ol713

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Re: Air system problem
« Reply #17 on: May 17, 2013, 10:07:33 AM »
Bob I have the AD2 so different, sorry. mine has a check valve on the top of the Cartridge with a ball valve there, it was stuck open.
Yes the in line should be replaced or rebuilt. It is just a little rubber ball and spring maybe an o ring. it should be the top hose to air dryer port in the big nut.

I also replaced my Pressure protection Valve 65 PSI 22.00 ceiling of the front bogie and right next to it is your type E filter. 4 bolts on the bottom corners and that comes down and the filter 3.40 drops out.

You might want to replace your compressors unloader pistons & spring, just get the unloader rebuild kit, 13.00
If you still have problems after that, then move to the rear axle area inversion valve, etc. Spray soapy water on all.
The 2 cap bolts on top of the compressor if take out there are 2 pieces of flat metal which over time get little circles pressed into them that don't allow them to close of the air fully and leak back through the compressor. If they have them on both sides it means somebody just flipped them over to save money and then they really should be replaced.
These are just some problem areas that relate to your problems that you might check , test, or replace. HTH

Dave5Cs


Hi Dave;
   Where did you buy a new "e" filter?
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Offline Bob & Tracey

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Re: Air system problem
« Reply #18 on: May 17, 2013, 01:07:44 PM »
Gus,

Nothing on this bus is original, everything has been upgraded with more modern systems. It has been running with these pressures since the 1980's when the 4106 drive train was installed.

Brian,

I will look at the check valve on the air dryer again, who knows may be I installed it incorrectly. Any idea where I might find the check valve between the tanks, or what to look for?

Bob
Bob & Tracey Rice    Full timing until it is no longer fun.

1956 GMC PD4104

Offline gus

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Re: Air system problem
« Reply #19 on: May 17, 2013, 02:20:00 PM »
OK, I didn't know about the 4106 drivetrain so that leaves me out!

However, the drivetrain change wouldn't have necessarily changed anything else, except for the addition of the dryer, since all the change is in the rear and independent of the air system except for the comp.



PD4107-152
PD4104-1274
Ash Flat, AR

Offline Bob & Tracey

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Re: Air system problem update
« Reply #20 on: June 10, 2013, 11:06:46 AM »
Thank you to all who tried to help.

After using the ides put forth here and many others I finally gave up. I found a rebuilt dryer at a good price on ebay and now problem solved...

Thanks again,
Bob
Bob & Tracey Rice    Full timing until it is no longer fun.

1956 GMC PD4104

Offline Dave5Cs

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Re: Air system problem
« Reply #21 on: June 12, 2013, 06:03:27 PM »
Merle sorry haven't been back for awhile. You can take it into NAPA and they should be able to match it up.

Dave5Cs
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