M2-106 Air leak

[hemsteadc]

2008 FL M2-106 Sportchassis,  8.3L Cummins ISC.  

Need help with air leak. Just spent 3 hours at the Freightliner shop in Hurricane UT trying to find my newest leak. No joy.  Symptoms are:  Pressure gauge (just 1) reads 50lb after 24hrs, almost zero after 48 hours.  Cab bags deflate - cab sags. Passenger seat won't stay up for even 1/2 hour.  Driver seat ok. All other bags ok.  Hydraulic brakes.

Air tanks (2) appear ok, drain valves ok. I've sprayed every fitting I can see with no signs of leakage.  

Wassup with this?
 

[Chad Heiser]

I would start with the lines and connections going to the passenger seat (if it truly is deflated in half an hour).  This would be my guess as to where the leak is.  These are not cheap, but they can be worth their weight in gold when tracking down air leaks.  A Whisper will often find leaks that bubbles won't.  Many of the HDT members have one of these and we all swear by them for tracking down pesky leaks.

[Bobi and Dick McKee]

We too have a leak somewhere.  Sometimes it will stay up for day, then after a short drive it drops to 50#s over night.  We arrived home Saturday and I ordered a whisperer like Chad mentioned.  Figured it would cost $200 to take it to a dealer and with all the lines I will probably have another leak down the road and will need the whisperer again.  Dick

[hemsteadc]

Thanks.  Why doesn't the shop have one of these?  Yes, I would agree it's likely the seat, but with a leak that substantial I'd think I'd hear something.

[Chad Heiser]

I showed my whisper to the service manger at the local shop I use.  He had never heard of such a thing either.  You would think that any place that works on air systems would have one, but then that would just make too much sense.  It would also cut down on the number of hours they could charge for when trying to track down air leaks. 

 

[hemsteadc]

26 minutes ago, Chad Heiser said:

. It would also cut down on the number of hours they could charge for when trying to track down air leaks. 

 

Really. I need to learn to quit paying "professionals" to do things I can and should do. I can't install a turbo, but  I sure could find my own air leaks.

[ms60ocb]

The Seat Air is a major issue. Have have several problem, Mechanical linkage came disconnected caused air leak, Hose connectors leaking but repeated until the length of  hose increased to reduce stress. I had an under the dash leakage at the hose supplying air to the air bags on my FW Hitch, My 2015 Sports Chassis had a Cab air bag replaced this spring for the only air leakage outside the Cab.

Clay

[Alie&Jim's Carrilite]

I put a valve on my seat.

Works great when I remember to use it.  

[hemsteadc]

thanks.. good tips.

[RBH]

Air/water bleed valve on the forward tank has been my continuing problem. Crud gets into the valve then it won't seal up. I've taken it off a few times and cleaned it out but nothing lasts. After every use it refuses to seal because rusty crud in the tank keeps fouling the seal.  Finally decided that since I was crawling under a couple of times a year to remove and clean the valve anyway I would just replace it with a plug. I can bleed off the air with the air hose hook-up then remove the plug to drain. I sure wish they would have used stainless steel to make these tanks.

[beemergary]

Kids bubbles works great for finding leaks. Air can back feed thru air commpessor. I have a 1984 Peterbilt-twin axles-air operated trans.-air windshield whipers-differential locks-three air tanks-etc. The old girl will hold air for a week-seats for months and air bags a month. I have found quit a few leaks and a big culprit was the air horn valve above headliner.

[hemsteadc]

I gave them 3 days in the shop this time instead of 3 hours.  They found 3 leaks: the seat switch, and 2 others, but the gauge pressure is still dropping overnight and the cab is sinking.  Passenger seat stays up.  

I don't get it.  That's a pretty substantial leak, or so it seems to me. Perhaps this shop just isn't very good at leaks, or is lying to me..but I kinda doubt that.  And they don't have the sniffer as mentioned earlier, just soap bubbles.

Air horn switch.. hmm, that's a thought..thanks. And since the cab is falling, I'll make sure they look at the cab air bags next time.  For now, I'll just put up with it, but I hate driving around with known problems that usually just get worse at the worst possible time.

Anyone ever had service at Freightliner in North Las Vegas?

[Chad Heiser]

I had a pesky air leak that I couldn’t find, even with the whisper.  My cab would fall first and then slowly, everything else would go down when I was parked.  I finally just replaced my cab leveling valve as a preventative measure.  I don’t know when or if it had ever been changed.  Now my truck stays aired up for multiple days without going flat.  If I leave it long enough, it will eventually drain, but it takes a long time now.  The cab leveling valve was pretty cheap and pretty easy to replace.  Just a thought.  My leak was small enough, the whisper couldn’t detect it, but still big enough to allow it to go flat over night.  I suspect the leak was internal to the valve, which made it very hard to detect.

[hemsteadc]

Thanks Chad.  Next visit to the shop will include that specific item along with a few others.  Hard to know what is simply annoying vs. what is critical.

It was critical when the rear suspension bags were falling overnight while hitched up.  That was a simple plug in the jct box near the rear axle.  This... this is much more difficult.

[hemsteadc]

There must be a schematic for the air system.. somewhere.. maybe?

[ET156]

I had a leak that doing the same thing I could never find to source so pulled my dash a part and there it was my dump valve for the rear air bags was leaking at the solenoid. installed a new fitting and now no leaks psi stays up at 120psi. 

[hemsteadc]

For now I'm just living with it.  Rear bags stay up, but cab still falls o'night and pressure usually reads about 50.  I inflate in less than 90 seconds so I guess that's acceptable for now.  

[SMEE]

Not sure if this will help but I had an issue with the cab bags leaking down.  I never found a leak to fix but I put a check valve in the line before the bags.  Never had in issue since and all it takes is to cut the line and insert the valve. Compression fittings so no tools needed  only cost a couple bucks so very cheap fix. 

[hemsteadc]

19 hours ago, SMEE said:

.. I put a check valve in the line before the bags.  

Nice idea. That valve blocks any leakage From the air bags to wherever the leak is. (?) Leaks are impossible for me to find, and nearly impossible for the shops I've been to.  Nobody has any kind of leak detector other than a bottle of soapy water.

I'm just not the kind of person to allow small problems to become large ones (since they tend to do that when you're nowhere near a shop) , but in this case, that seems to be the most reasonable choice.  

[Undrpsi]

Had similar problem losing all air over night. Found my cab air bags were leaking. Changed them out and air stays up for almost 3 days. Easy fix.