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Old 06-15-2012, 10:29 PM   #1
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Question Woah! Loud bang from left side!!!

Hi,
I firmly believe no question is a dumb one...please bare with me.
We just got our first diesel bus. We are super excited, but they taught us zero! So, my question is....after it starts up, there is a loud bang on the drivers side towards the rear. Despite the Tupperware bin of manuals my Hubbs is scouring for the answer....I thought I'd ask if anyone else has experienced it, or has a clue what it is. It has happened twice now. We start the vehicle, wait for the alarms for the....I dunno air?, then about 2 mins late - POW! Sounds like a backfire.
Help please! And thank you in advanced!
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Old 06-15-2012, 10:38 PM   #2
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Well, one possibility is that it is the air compressor releasing air when it reaches its maximum compression (usually when the air pressure reaches the 135-150 PSI range). It''s the compressor releasing any water and dirt that builds up when air is compressed in the air compressor.
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Old 06-15-2012, 10:48 PM   #3
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The psi reading is at 10....shortly after. Whats that? I'm really clueless! I'm so sorry, any info is so appreciated.
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Old 06-15-2012, 10:55 PM   #4
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So when it releases the air.....it sounds really loud....similar to a weapon discharge. Is that right?
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Old 06-15-2012, 11:01 PM   #5
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I presume you have air brakes and have 2 pressure gauges-one for the front brakes and one for the back brakes. When you first start your motorhome, if the air pressure is below a certain level (usually 50-60 PSI), an alarm should sound. Once the air pressure reaches a certain level (usually 125-135 PSI), the air compressor should stop and this is usually when the air compressor will 'whoosh' with a discharge. It can be a loud sound. What is the pressure when the alarms stop?
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Old 06-15-2012, 11:08 PM   #6
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Not sure where you live but most states and Canadian provinces require you to get a license to drive a vehicle with air brakes (sometimes referred to as air brake endorsements). You might want to find out if there are courses available to learn about air brake systems. Usually these are offered through truck driver training companies and they will teach you alot about how your air system works. My wife and I took a course and it taught us about all the components that make up our RV's braking system.
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Old 06-15-2012, 11:12 PM   #7
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Ok, it is 125 psi when the alarm stops. My Hubbs is laughing because your whoosh sounds like a gun! Lol it's not that whoosh similar to what I've heard from a city bus, it a POW like a freaking backfire! It makes you jump out of ur skin if your outside. :-(
We drove it from NJ to NC (bought in NJ) - but other than that, it's been in our driveway. Should we take it into a shop? It's brand new.
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Old 06-15-2012, 11:13 PM   #8
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It can be quite loud (yes, it could sound like a bang). You may also hear it occasionally when you are driving after you have used your brakes.
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Old 06-15-2012, 11:22 PM   #9
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The sound I hear from my air system isn't the kind of POW that you describe. However, if I were you, I'd contact the dealer or manufacturer to get their opinion.
Without putting yourself in danger, you might want to listen in the area where the loud sound is coming from to see if you can isolate its location. My bet is that it is coming from your air compressor.
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Old 06-16-2012, 08:58 AM   #10
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From time to time my coach will make a very load pop noise. Very different from the air release. What I have found it only happens when there is a excessive slope when you level your coach to camp. Then when you start up to move the air bags re seat them self. I have had it on the front of the coach. Like I said it only happened when it was a big slope and the suspension was stretched out.
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Old 06-16-2012, 09:13 AM   #11
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I ocasionally hear the bang you are talking about. I think that it occurs when the air bags are filling and causing the suspension to line up when they fill. When the air bags are full and the pressure is up to specs, you will hear as others have said, a whoosh for the release of air. I don't believe that it is anything to worry about. JMHO.
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Old 06-16-2012, 10:09 PM   #12
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I would also suggest that it is a suspension air bag that is not seated properly - the sound would be very similar to that heard in a tire shop when they are inflating new tires and the bead pops into place. One problem that I notice is that if your air 'alarm' is still sounding at 125 psi something is amiss. The alarm should cut out no higher than 70 psi - by 125 psi, the compressor should be cutting out.
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Old 06-16-2012, 10:50 PM   #13
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I heard that same type of pop/snap noise when getting ready to leave a sidehill slightly unlevel campsite while waiting for the airbags to inflate. It made me worry at the time but was probably not a problem.
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Old 06-17-2012, 01:33 PM   #14
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Ok...so it could be because our driveway is slightly not level, and it only happens after we have brought up the levels and then start it. Phew! Thanks folks for all your insight and guidance! It's much appreciated - especially over a weekend when you can't call or get in touch with anyone! :0) This forum ROCKS! :0)
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Old 06-17-2012, 07:01 PM   #15
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Relax and enjoy your beautiful new coach, Newgurl
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Old 06-19-2012, 12:14 AM   #16
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load noise after starting

A few things on you note do not make sense to me.

1) Your low pressure alarm should shut off well before 125 lbs since normal operating pressures are between about 90 and 130 lbs.
2) You mentioned a pressure of 10 lbs. Please note that the single pressure guage on the left of the wheel is a turbo boost. The two airbrake guages are located on the cluster to teh right of the wheel.
3) The compressor for your airbrakes is designed to operate at all times when the vehicle is running. Once the maximum pressure is reached, you should hear air being released by the pressure relief valve (like when you are on a bus).
4) A load ... gun like noise comming from your coach is not normal. If it continues, I would highly suggest taking it into a Freightliner dealer for an inspection.
5) Once of the posters suggested getting you airbrake ticket or Q certification. Speaking from personal experience ... this was some of the best money I have ever spent. Air brakes are very different from the type of brakes that you have in you car .... it is possible to get yourself in a whole bunch of trouble in a really short time . Example ... if you are someone who rided the brakes on a hill, it is possible to very quickly use up all of the reserve air in the two holding tanks.... at which point you loose control of your brakes and you are in danger of your brakes locking up. Example two ... if you have a leak in the system and do not stop teh vehicle before all air is depleated ... your brakes will lock up with over 3000 lbs of force and will require professional service to release them. (Image this happening in the middle of a rail crossing with a train coming).

I have gone through the unpleasent experience of having one guage falling to zero as I was driving on a mountain road. This was one of the most stressful times of my life.

Please do yourself and those around you a favor and get your airbrake ticket. It takes 2 days and cost about $100

Good Luck

ps
Once you learn how to use them ... you with love the combination of air brakes and engine retarder
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Old 06-19-2012, 07:24 PM   #17
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I think if I hear a back fire sound from my air system I would get it checked out. A woosh sound that all large bus's and trucks make is normal and that's what mine does.. It can be loud in your driveway but I could never describe it as a bang or backfire sound.. I would get on the phone with your dealer or your local Freightliner shop and have them check it out.



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Old 06-19-2012, 07:29 PM   #18
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One other thought when you deal with Freightliner make sure the are comfortable working on MH. I just went to drop our MH off at the Grand Rapids Mi shop and was talked out of leaving it. They told me they would rather not work on them as they were not set up for MH.. I need to call Kalamazoo MI about an hour away to have warranty work done..



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Old 06-19-2012, 08:33 PM   #19
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Have you tried finding your air dryer? That is where the whoosh or popping sound will come from when you have reached max air pressure. Locate it and let pressure build until you here the pop. A short blast of air will come out the bottom of it. If that is the sound you hear then I wouldn't worry, if the sound is coming from somewhere else get it checked out!!!!! Also the alarm should go silent well before 125 psi.
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Old 06-19-2012, 08:38 PM   #20
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Also please do anything you can to familiarize yourself with an air brake system. Cannot emphasize that enough!!!!
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