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Old 11-30-2018, 09:07 AM   #1
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PAC brake sound?

Wanted to ask about this PAC brake, What is it supposed to sound like when it's activated?
I get a moderately loud whooshing air sound is this right or do I have something leaking air, like a hose or the CAC?
The exhaust brake slows me down some not as much as I would like.
this is the only coach I have ever driven so I have nothing to compare it to,
I know the higher my engine RPMs the better it works,
also how do you test to know if it's working properly ?
I have observed it closing and opening the butterfly valve and it's rotating all the way it seems,
Thanks,
Benny
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Old 11-30-2018, 10:03 AM   #2
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It sounds like nothing. It sounds like your big gas engine when you close the throttle, because that's about all a PAC brake is. You may be thinking about the compression release brakes you hear on those big 80,000+ pound semis. That's not a PAC brake, and you're a 30-40,000 motorhome. A PAC brake is a plate that closes in the exhaust flow before the turbo that causes pressure in the exhaust stroke, to slow the engine. Now, you Allison likely downshifts at the same time as PAC brake activation, you can hear and feel that. But the PAC brake itself is very quiet.


When you see the sign that says "NO COMPRESSION BRAKES", ignore it. It's misworded and doesn't apply to us.
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Old 11-30-2018, 10:09 AM   #3
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Signs should say " No unmuffled compression brakes". Compression brakes are muffled now.
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Old 11-30-2018, 12:03 PM   #4
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Quote:
Originally Posted by benford View Post
Wanted to ask about this PAC brake, What is it supposed to sound like when it's activated?
I get a moderately loud whooshing air sound is this right or do I have something leaking air, like a hose or the CAC?
The exhaust brake slows me down some not as much as I would like.
this is the only coach I have ever driven so I have nothing to compare it to,
I know the higher my engine RPMs the better it works,
also how do you test to know if it's working properly ?
I have observed it closing and opening the butterfly valve and it's rotating all the way it seems,
Thanks,
Benny
I hear the "whooshing air sound" through my rear camera mike when the PB is engaged.

The PB braking force seems to be similar to the Allison downshift braking force and most of the time they occur simultaneously.

Mine does not work in excess of 65 mph nor does it have a very noticeable effect below 30 mph.

You might test the PB force by raising foot off the throttle at say 50mph to get the Allison downshift engaged and then turning on the PB to see if there is a noticeable braking effect.

Or, compare the downshift from high speed, foot off the throttle scenario with the PB on and then PB off.
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Old 11-30-2018, 12:35 PM   #5
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Quote:
Originally Posted by deandec View Post
I hear the "whooshing air sound" through my rear camera mike when the PB is engaged.

The PB braking force seems to be similar to the Allison downshift braking force and most of the time they occur simultaneously.

Mine does not work in excess of 65 mph nor does it have a very noticeable effect below 30 mph.

You might test the PB force by raising foot off the throttle at say 50mph to get the Allison downshift engaged and then turning on the PB to see if there is a noticeable braking effect.

Or, compare the downshift from high speed, foot off the throttle scenario with the PB on and then PB off.
That's what I needed to know thank you,
My coach only has a four speed Allison, it doesn't downshift until below 50 I think,
I suppose mine is working right, I was curious about the sound it makes
thanks for the replies
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Old 11-30-2018, 12:40 PM   #6
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Oh and I wanted to share a pic of my new floors , installed by Ernie Ekberg
He is the master at flooring installation in a coach, it's Beautiful
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Old 11-30-2018, 12:43 PM   #7
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Oh and I wanted to share a pic of my new floors , installed by Ernie Ekberg
He is the master at flooring installation in a coach, it's Beautiful
ok here
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ID:	227615   Click image for larger version

Name:	new floor 2.jpg
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ID:	227616  

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Old 11-30-2018, 02:00 PM   #8
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you were in good hands... nice!

just so you know, if turbo housing leaks air, your exh brake won't be as effective though the gate is closed.
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Old 11-30-2018, 02:34 PM   #9
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Very nice!!
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Old 12-01-2018, 09:49 AM   #10
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ok here
Floors look great, where is Ernie located?
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Old 12-01-2018, 12:48 PM   #11
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Floors look great, where is Ernie located?
Weatherford Texas, he has a Facebook page if you want to contact him
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Old 12-01-2018, 01:09 PM   #12
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Quote:
Originally Posted by benford View Post
Wanted to ask about this PAC brake, What is it supposed to sound like when it's activated?
I get a moderately loud whooshing air sound is this right or do I have something leaking air, like a hose or the CAC?
The exhaust brake slows me down some not as much as I would like.
this is the only coach I have ever driven so I have nothing to compare it to,
I know the higher my engine RPMs the better it works,
also how do you test to know if it's working properly ?
I have observed it closing and opening the butterfly valve and it's rotating all the way it seems,
Thanks,
Benny
Here is a document that may help answer your questions.
Attached Files
File Type: pdf pacbrake.pdf (838.2 KB, 23 views)
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Old 12-01-2018, 02:01 PM   #13
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Quote:
Originally Posted by benford View Post
Wanted to ask about this PAC brake, What is it supposed to sound like when it's activated?

I get a moderately loud whooshing air sound is this right or do I have something leaking air, like a hose or the CAC?

The exhaust brake slows me down some not as much as I would like.

this is the only coach I have ever driven so I have nothing to compare it to,

I know the higher my engine RPMs the better it works,

also how do you test to know if it's working properly ?

I have observed it closing and opening the butterfly valve and it's rotating all the way it seems,

Thanks,

Benny


Benny, it does sounds like a big air leak. You can manually downshift as well.
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Old 12-02-2018, 09:43 AM   #14
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When my PB is on low and standing still I can hear a hissing sound. When in high standing still I hear nothing.
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