How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Wayne Your Own Question
Wayne, Journeyman
Category: Medium and Heavy Trucks
Satisfied Customers: 9677
Experience:  worked on, Gmc, Macks, Freight liner,Mercedes Benz,,Ford, sterling
Type Your Medium and Heavy Trucks Question Here...
Wayne is online now
A new question is answered every 9 seconds

I have a 2006 Tiffin Allegro Bus on a Freightliner chassis.

Customer Question

I have a 2006 Tiffin Allegro Bus on a Freightliner chassis. Last 6 of VIN are X74711. On a recent trip I experienced a problem with the "front air" when in traffic on a very hot day with my generator running so I could run A/C. A very loud scream started and just continued so I pulled into a rest area and cut the engine off. The scream was coming from the front area between the front tires but stopped after a few seconds. I didn't notice any other symptoms that day as I stopped at a Walmart about 20 minutes away. The next day again with the same situation it happened again. I stopped again and shut the engine off. Again the scream stopped after a few seconds. I continued not running the generator and all seemed okay then started the generator and after a while started to notice that the front air pressure gauge was constantly building pressure to 125 then loosing pressure down to 90 psi. I shut off the generator and after a while the front air pressure stopped varying and was normal again. My guess was that the issue was heat related. I stopped at a Freightliner service center in Roanoke VA the next morning and one of the service technicians crawled under the front of my RV but found nothing obvious. He suggested maybe the "dump valve" but said that they couldn't get to us for a couple days at the earliest. We continued on our trip for a month without any further problems but didn't run the generator while driving. Would like to get the issue resolved but don't know how to duplicate the problem in a controlled situation. Any help would be greatly appreciated.
David Pouliot ***@******.***
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Wayne replied 1 year ago.

Hi I'm Wayne

I will try to help you with this

did it sounds like a high pitch Squeal?

Let me know

Customer: replied 1 year ago.

Yes. Like letting the air out of a balloon but much louder.

Expert:  Wayne replied 1 year ago.

Thank you for that

OK, what you are describing is the air drier

is plugged up and malfunction, seen this many times

and yes the heat is a a factor, what is happening the

relief valve is purging air out and sticking open

I suggest to have the drier replaced

I hope this helped you

Hi. If this helped you,

please remember to rate my answer 3 or more stars.

If more info is needed, use the reply button -


Expert:  Wayne replied 1 year ago.


Just a follow up with you

did my answer help you

let me know, please