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Brake(s) air pressure low…


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   1. 2005 Beaver Marquis

   2. RV was in storage for 12-months

   3. Normally… upon starting, the brake “air pressure low alarm” will sound for a couple of minutes (until ~70-PSI has been reached

   4. Now… after starting (since being in storage) and while sitting at idle, the air pressure will only reach about 65-PSI.   Thus causing a continuous low pressure alarm condition.  

HOWEVER… IF the the engines RPM’s are increased for a couple of minutes, then the pressure will build-up and stabilize around 90-PSI on the low end.  From there… the air pressure will then fluctuate between ~90-130 PSI, until sitting in an idle condition for longer than about 3-4 minutes.  I’ve also noticed that the fluctuation time seems to be faster if going up hill…


I suspect a small air leak somewhere and the “fluctuating” of the air pressure (between 90-130 PSI) is due to the cycling of compressor…. ?


Any thoughts and/or recommendations are appreciated!


thanks in advance,


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Normally you may be starting with some air in the system… mine takes for ever to build if I don’t increase the rpms to 1200. I do a brake test once the compressor unloads at 135psi… release the parking brake and put the brakes on and hold for 30 seconds. Pressure should lower but then remain the same while holding the brakes on. After releasing, the psi should not change for 30-45 seconds.  If doing a CDL test you hold for a minute but allowed a 4 psi drop.

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All, huge thank-you for all of your suggestions, I sincerely appreciate it!

Today we’re in Moscow IA, and we have an appointment the “mothership” of HWH.  (having our leveling and slides “checked-out”). Tomorrow… I’ll start digging into the low air pressure on the brakes again (I’ll post my findings as I come across them)

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Had a a similar problem...turned out to be the brake air chambers.  Rubber diaphragms had deteriorated.  2005 date codes inside chambers on a 2010 Neptune assembled in 2009.  Parts readily available and not too complex a repair.  A rear one was bad, changed out all 4 in the interest of safety and peace of mind.





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Those Brake Air Chambers are readily available at most truck repair shops. I had to replace one on a rear wheel in northern British Columbia as the tow truck driver attempting to Cage the rear brakes before towing was only able to do one side. The other side had an internal problem and wasn't able to Cage the brakes on that side.

The front wheels only have an Service Air Brake Chamber whereas the rear wheels have a combination of a Service Brake & Spring Air Brake Chamber.


Hv-s08 T30 Service Brake Chamber For Heavy Duty Truck - Buy T30 Brake  Chamber,Service Brake Chamber,T30 Single Chamber Product on Alibaba.com

Trucks: How does an air brake work? - Quora

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  • 3 weeks later...


I'd like to start-off by sincerely saying "THANK-YOU" to everyone for their comments and assistance regarding this!!!



Ultimately and unexpectedly..., we ended up having two completely separate air line holes (I intentionally didn't use the word "leaks"...)

- One hole, the original problem, was pretty severe and was extremely loud.  Upon finding this hole, I was able to repair that line.  This particular hole is what was causing the compressor to constantly oscillate from ~90PSI - 120PSI.


- Three-four days after experiencing the original "hole", a second hole developed near the compressor itself and luckily happened after we'd parked!!!  (the two holes were about 15-20 feet apart and were completely unrelated to one another) This particular hole wasn't nearly as loud and/or physically noticeable, however... because it was coming directly off of a compressor line, this hole prevented any air pressure from building up whatsoever...  (This hole was caused due to a flexible air line which had been vibrating & rubbing up against the starter solenoid, which... in-turn caused intermittent starting issues)


FWIW - I found the hole that was coming directly off of the air compressor first.  Upon replacing the flexible tubbing, that was when I was able to hear the original hole.  


When it's all said and done, the two air line holes have been repaired and/or replaced, along with the starter solenoid.


Thanks again to everyone for assisting, and your words of wisdom!!


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