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Another air leak question

April 05, 2019, 07:43:34 am

1987 GV cat3208. Compressor builds up to 120ish pretty quick and dryer purges, air falls pretty quick down to 105ish, then back to 120. It's cycling and purging about every 15-20 seconds. Shut motor off and gauge is steady so it's only leaking when motor is running. So far Ive sprayed soapy water on all lines coming from governor, and air dryer, purge valve, and adjusted the governor up and down and it seems to be doing what it's suppose to. What else could it be?

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Re: Another air leak question

Reply #1 – April 05, 2019, 09:22:18 am

When it's running are you releasing the parking brake or do you have your foot on the brake? You should be able to
Hear a leak that big. Does you air compressor have intake line that goes to the air cleaner, if that may be where your leak is. Just fishing here.

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Re: Another air leak question

Reply #2 – April 05, 2019, 09:32:33 am

Mine did that when I picked it up and drove 1400 miles home. Replaced the $15 D2 valve that governs the compressor air production. 30 minute job, carry a spare with you. I walked into a truck parts shop and told the guy a D2 please, his response was how many, while he reached below the counter and pulled one out.

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Re: Another air leak question

Reply #3 – April 05, 2019, 09:36:20 am

Adding to Bruce's ideas...

Also check anything that is directly connected to your wet tank.  Not familiar with your model coach, but on my coach that would include the water drain line and remote valve, and the line to tire filler air hose connection.  You should have inlet check valves on your front and rear (brake) air tanks that if working properly will not allow back flow to the wet tank.  Therefore, a massive leak from the wet tank while engine is running will not show up on your dash air gauges when engine is shut down.

Probably doesn't apply to your coach, but...  I also have a air operated exhaust brake on our coach.  The air supply for the brake T's off the tire filler air line.  I once had a large leak at the pressure regulator in the exhaust brake supply line.  That one had me scratching my head for quite a while cuz it was hidden up above the bundle of wires and hoses exiting the center utility tray into the engine compartment.

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Re: Another air leak question

Reply #4 – April 05, 2019, 09:47:19 am

Have you turned the key on without the engine running? Haven't run into symptoms like yours with lots of air brake experience.

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Re: Another air leak question

Reply #5 – April 05, 2019, 09:58:37 am

I haven't tried it with key on yet, will try this afternoon. Could it be the unloaded valve? I may be the d2 but it seems that it's doing it's job, the compressor is kicking on at 105ish and purging around 120ish. I will start checking all over with soapy water after work today. I do have a tiny leak in my right rear air bag, but it takes 15 minutes to drop 10psi with the key off, so pretty sure that's not the cause of my compressor to be cycling so often.

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Re: Another air leak question

Reply #6 – April 05, 2019, 10:06:03 am

The unloader valves are not connected electrically and there is a check valve that prevents air going back to the compressor and if the check valve was bad it would leak air with the engine off.

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Re: Another air leak question

Reply #7 – April 05, 2019, 10:16:43 am

I had thought that you had changed the D2 .  A new one will raise the pressure to 110/130, Brakes work better, etc.  As prior mentioned, when the D2 is removed , spray a little  light oil into the compressor ports.

 If both air gauges read very close to the same, the leak is prior to the tanks.  Charge line, air dryer  relief line.  There is a line that lets pressure off of the compressor head as the dryer purges . 

 This has only 2 air tanks. 
 Do the D2  and light oil , get back to us. Thanks,MM

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Re: Another air leak question

Reply #8 – April 05, 2019, 02:58:02 pm

Thanks everyone! Will put a new D2 on it and shoot some oil in there and let you guys know!

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