Hiss Sound When Pac Brake Turned on What do you think it is?

[Skip4Josh]

Hi we got this Coach the begining of January and drove it home from Florida. We had a leaking pinion seal which we have replaced. Took the coach out yesterday for a test ride the 1st time since bringing it home from Florida and now as Soon as Pac brake is activated I hear what sounds like an air leak coming from the rear, everything seems to be operating normal, I have boost readings when on the throttle and coach idles and sounds fine, would love to hear what you think it might be or where to look, I also can smell some exhaust in the coach, I did on the way home from Florida with it too but just thought something wasn't sealed properly, now I'm thinking might be related?

[Ray,IN]

The Cummins ISC is well known for breaking exhaust manifolds, as the entire weight of the turbo and associated piping rests on the manifold.
Remove the engine cover in the bedroom, start engine, watch and feel for any air/exhaust leaks.
Mine was obvious, one side of the two-piece manifold was broken entirely through, and the manifold gasket was leaking in 3 places..
Cummins redesigned the manifold to eliminate the problem, and it is much thicker and heavier than the OEM manifold.

I had it replaced at a local HDT repair shop. I first removed the entire bed and stand, then covered all the coach carpeting with the sticky carpet protector. Had I not done that, my total bill would have been much higher, as it was the total bill was $3,000. Do not attempt to replace only one half of the manifold, it will never seal properly.

[kenwyatt]

Doubt the Park break hiss and exhaust smell are related. Air up your tanks, shut the engine down and set the brake. Every park break on any air break system sets the brakes by releasing air and letting springs set and hold. If the hiss goes on more then a very short amount of time you should be able to locate it

[Skip4Josh]

Originally Posted by Ray,IN

The Cummins ISC is well known for breaking exhaust manifolds, as the entire weight of the turbo and associated piping rests on the manifold.
Remove the engine cover in the bedroom, start engine, watch and feel for any air/exhaust leaks.
Mine was obvious, one side of the two-piece manifold was broken entirely through, and the manifold gasket was leaking in 3 places..
Cummins redesigned the manifold to eliminate the problem, and it is much thicker and heavier than the OEM manifold.

I had it replaced at a local HDT repair shop. I first removed the entire bed and stand, then covered all the coach carpeting with the sticky carpet protector. Had I not done that, my total bill would have been much higher, as it was the total bill was $3,000. Do not attempt to replace only one half of the manifold, it will never seal properly.

Thanks for the input, That's kind of what I was leaning towards... I know we will be doing the work ourselves, not really looking forward to it though, we just got done replacing all the coolant houses and fluids what a PITA, but we're are very particular with maintence.

[Skip4Josh]

Originally Posted by kenwyatt

Doubt the Park break hiss and exhaust smell are related. Air up your tanks, shut the engine down and set the brake. Every park break on any air break system sets the brakes by releasing air and letting springs set and hold. If the hiss goes on more then a very short amount of time you should be able to locate it

PAC brake exhaust brake not parking... Parking brake is working as it should applying automatically between 40 and 20psi and holds the coach while in gear at idle thanks though

[Kuzzy]

Are you sure it’s not just the sound of the PAC exhaust brake?
I hear hissing from my Cat engine exhaust when I flip the switch for the exhaust brake. It’s normal.
If your air pressure is steady then all is good.
I would think if your exhaust manifold was cracked you would hear it under power too.

[irishguy]

Our pac brake hisses and there is an odor in the coach when it's being used. I've had it checked out twice by my long time heavy truck service centre.

They said it is working normally and that a relief valve on the side of the pack brake relieves pressure under load and makes a hiss sound.

The four year old exhaust manifold is not the issue and is not cracked.

From what I've read on here, exhaust manifolds crack from excessive heat. Nothing related to the pac brake.

Other posters on here have said the hissing and smell is normal while other's have said it's not. So who knows for sure.

irishguy

[Skip4Josh]

Kuzzy,
I'm not sure I do know that it didn't make that nose when we 1st got it, air pressure are fine so are all other pressures. Unfortunately this Coach is new to us and that was the 1st time we had it out since bringing it home 4 months ago so we don't know it well yet.

Irishguy,
My odor is constant in the coach all the time not just with PAC brake engaged, I can smell it up front all the time, it has me concerned with co2 getting into the coach, and I just don't remember the hissing before.

[jacwjames]

My exhaust manifold failed back in 2015. I noticed the difference in sound immediately and went back and pulled the closet hatch to confirm.
I changed the manifold myself, took a little time but not bad. I spent quite a bit of time having to get up, go outside, crawl under the engine, and pick up tools/nuts/bolts as I dropped them. So if you have a helper it would be better.

At first I tired to work around the turbo, leaving it hooked to the flexible exhaust pipe but I ultimately removed which made it much easier to get the manifold off/on.

It cost me ~$650 for parts.
I've read where some people have paid almost $4K to have it changed. Yikes.

[Kuzzy]

Just a thought.
Could it be one of your bedroom windows are open?

[RKins]

Are you saying that as soon as you turn on the exhaust brake enable switch on the dash or wherever yours is, you hear the hissing? Mine hisses when it activates and I hear nothing when it doesn't activate. I have to lift the bed up to hear if it is working. The rules are the pac brake is enabled and will not activate until your speed is above 10 mph. I added a footpedal so I could override that operation and I can activate it anytime.

[mike brez]

Normal. start up and put pac brake on low you will hear hiss now put it high did it go away?

Exhaust smell something else

[RKins]

Originally Posted by mike brez

Normal. start up and put pac brake on low you will hear hiss now put it high did it go away?

Exhaust smell something else

Mike, a Pac brake is an on/off exhaust brake. I have not heard of a low/high pac brake. You must be thinking of a compression brake - different animal, but I don't think they hiss. Unless this is something totally new where the exhaust brake only closes partially or fully.

[palehorse89]

There is a hole in the butterfly plate in a exhaust brake, thus the hissing noise when in use.......