Community Forums

Zak · 06-22-2014, 07:03 PM

When I run my coach, it always sounds like air is constantly filling a cylinder or tank, up in the front, near the front end, or about 3' directly behind the back of the generator. Is this normal? It never stops...like a soft hiss of air going in when you filling a tire.

I don't think it's a leak per say as when I turn key off, coach does not lose any air pressure over time at all. I don't hear the compressor kicking in and out while driving and both air gauges never drop unless I hammer the brakes.

Anyone know what the noise is or if it's normal?

Thanks team!!!

PDR John · 06-22-2014, 07:27 PM

I'm going to say you have a leak, just a matter of where.

Here is what's behind the genny:

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PDR John · 06-22-2014, 07:28 PM

There is about 15 air lines up there.

Zak · 06-22-2014, 07:35 PM

Lovely...will have to bring it in to steinbring on start of a 30 day trip in a week then. It's on the way.

I'm not convinced its a leak though. Sounds more like air filling a tank constantly. If I shut engine down and it was a free leak, would pressure drop? I left coach aired up for 24 hours, still at 125 psi next day? I'm baffled.

Zak · 06-22-2014, 07:36 PM

Should I soap test that mess of lines and unions?

PDR John · 06-22-2014, 07:55 PM

I did have a leak where the line went into the tank, but you couldn't hear it.

I would soap test with engine on and off. make sure you block the frame with wood blocks or 15 ton jack stands.

Mine was on the hoist at HWH.

harleychief · 06-24-2014, 05:33 AM

Quote:

Originally Posted by Zak

Lovely...will have to bring it in to steinbring on start of a 30 day trip in a week then. It's on the way.

I'm not convinced its a leak though. Sounds more like air filling a tank constantly. If I shut engine down and it was a free leak, would pressure drop? I left coach aired up for 24 hours, still at 125 psi next day? I'm baffled.

Zak - Sounds as if it's a leak in the service brake system or a leak at the air bag. If you do a soap test make sure to do it with the parking brake on and off (of course chock the wheels first). The parking brake system unlocks the brakes with air pressure (not enough air pressure the brake engages), so when you're parked overnight the service brake side of the system is isolated, that may be why you don't leak air overnight. I'd have a helper apply, hold then release the service brake while you check for bubbles or the sound of air leaking. Remember, if it is a brake or bag issue the "leak" may be in the back and what you're hearing is the tank (behind the generator) refilling.
When you park overnight are the air bags inflated or deflated? If they're inflated and are still inflated in the morning I think you're pretty safe it's not the air bags. However, if when you park it the air bags are deflated, then I'd try leaving them inflated and see if the stay inflated.

PanJH · 06-24-2014, 05:41 AM

I could hear a hiss sound on ours and found that the lanyard for the tank drain valve was routed in a way that it had slight pressure on the valve and allowed it to leak out air.

Zak · 06-24-2014, 12:49 PM

had it in at freightliner today for inspection...they found no leaks at the primary tank or air bags.

called freightliner service line...told to check tubing between air dryer and compressor...then if not a leak there under operating pressure, to check the air dryer "pop-off" or "relief" valve for leak. my first question...would you hear that all the way up front under the front end...apparently yes, you would.

back to freightliner tomorrow am! my friend with a 2013 DS says his constantly makes a hissing air sound when running... now i'm on a mission to see this through and find out if it's normal or in fact an issue!

stay tuned sports fans!

Zak · 06-25-2014, 09:42 AM

Back at Freightliner this morning...

Second mechanic found the source of the loud, continuous air hiss under front end (when engine running)...

It is actually a oil line coming from the engine to the power steering box in the front. The oil passes through a valve and/or 90 degree elbow fitting and it (for whatever reason) hisses like air filling a tank...

I tried turning the front wheels side to side and sure enough...the sound changed audibly as the oil pressure in the line changed. For all i know, could be the Comfort Drive system.

Wonder how many of you out there with DS's or MA's on the XCR chassis have same noise? Anyhow, put this one to bed. No issues. Somewhat surprising to me though that neither Newmar nor Freightliner knew anything about it.

MJFZ · 06-25-2014, 06:30 PM

Quote:

Originally Posted by Zak

Back at Freightliner this morning... Second mechanic found the source of the loud, continuous air hiss under front end (when engine running)... It is actually a oil line coming from the engine to the power steering box in the front. The oil passes through a valve and/or 90 degree elbow fitting and it (for whatever reason) hisses like air filling a tank... I tried turning the front wheels side to side and sure enough...the sound changed audibly as the oil pressure in the line changed. For all i know, could be the Comfort Drive system. Wonder how many of you out there with DS's or MA's on the XCR chassis have same noise? Anyhow, put this one to bed. No issues. Somewhat surprising to me though that neither Newmar nor Freightliner knew anything about it.

I had the same issue on my 2012 DSDP. Freightliner in Gaffney removed the power steering orifice in the line and the noise went away. They explained to me the orifice is used to reduce steering kickback at full steering lock. After they removed the orifice I felt no difference in my steering at full wheel lock but was happy not to hear the hiss that was most pronounced when the steering wheel was in a neutral position.

Mike