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Old 01-27-2013, 01:02 AM   #1
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engine brake vs exhaust brake or both?

Hey fellow RVers.

On my coach it has a "exhaust brake" switch but it clearly functions as an engine brake, It just downshifts my trans when I let go of the accelerator.

My question is do any of you have both the engine and actual exhaust brake? Would having them both work together be OK?

Do you have a preference between the 2 if you could only have 1?

Just trying to think of another way to save the brakes physical

Thanks!
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Old 01-27-2013, 01:57 AM   #2
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An engine brake is far superior to an exhaust brake. 2 total different things and they both coordinate with the transmission. Not sure what exact engine you have but sounds like you have an exhaust brake. If you have a cummins isc or isb you will have and exhaust brake. A cummins isl can have and actual engine brake with a high low switch, and some isl models also have and exhaust brake. If your coach is the coachmen in your profile, you probably have an exhaust brake. I'm not certain on the cat engines but I'm sure others will chime in. Both will reduce brake usage but the engine brake being the better of the two.
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Old 01-27-2013, 07:28 AM   #3
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The engine brake, also called compression brake or Jake brake, is internal to the engine and is controlled by the engine ECM when the switch is turned on. It works in conjunction with the transmission which selects a lower gear, usually 2nd or 3rd, and alters the valve timing of the engine to turn it into a big air compressor. An engine brake will usually have a 2 or 3 position high/low switch in addition to the off/on switch.

The exhaust brake is a valve installed in the exhaust just downstream from the turbo which restricts exhaust flow out of the engine when it's engaged, creating back pressure in the engine. There is another type used in some Cummins engines which use the VG turbo in the same manner. Exhaust brakes also downshift the transmission when activated.

Both types will help you save your brakes. The engine brake is more powerful and is generally available in larger diesels. The only engine I'm aware of which can be equipped with either, depending on how it's ordered is the Cummins ISL.
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Old 01-27-2013, 07:38 AM   #4
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[QUOTE=Magoogle;1443927]Hey fellow RVers.



My question is do any of you have both the engine and actual exhaust brake? Would having them both work together be OK?





Thanks![/QUOTE
My friends Frieghtlinner M2 has a Mercedes-Benz engine in it with both, on low the exhaust brake is activated and on high both the exhaust and engine brakes are activated. I was shocked when I saw it had both of them.
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Old 01-27-2013, 10:09 AM   #5
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My Coach has the cat 350hp c7 btw not a cummins.

With the exhaust brake would you not notice a specific sound? When you hear big rigs hit there exhaust brake that is very specific sound to it.

As far as I know it only down shifts the tranny.
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Old 01-27-2013, 10:33 AM   #6
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Quote:
Originally Posted by Magoogle View Post
My Coach has the cat 350hp c7 btw not a cummins.

With the exhaust brake would you not notice a specific sound? When you hear big rigs hit there exhaust brake that is very specific sound to it.

As far as I know it only down shifts the tranny.
Your c7 is only an exhaust brake and not comparable to an engine brake used by the big rigs. Total different technology. And yes an exhaust brake is quieter than an engine brake. You will likely hear more the tranny downshifting and possibly a little air sound from the back pressure of the exhaust brake. The engine break is internal to the engine and you will hear more of that cracking or thudding sound.

An engine brake is much more effective.
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Old 01-27-2013, 10:43 AM   #7
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Originally Posted by Magoogle View Post
My Coach has the cat 350hp c7 btw not a cummins.

With the exhaust brake would you not notice a specific sound? When you hear big rigs hit there exhaust brake that is very specific sound to it.

As far as I know it only down shifts the tranny.
You do have more than just the transmission downshifting. It's just more subtle than the internal engine brake - and less effective.
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Old 01-27-2013, 11:02 AM   #8
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Quote:
Originally Posted by Magoogle View Post

My Coach has the cat 350hp c7 btw not a cummins.

With the exhaust brake would you not notice a specific sound? When you hear big rigs hit there exhaust brake that is very specific sound to it.

As far as I know it only down shifts the tranny.
I don't think you will find an Exhaust Brake on any expensive OTR big rigs that are used in the trucking industry.

They all come with Engine Brakes or Compression Brakes and that's why they sound as they do, usually quite loud. Also, as you travel, you will see signs stating No Engine Brakes, Please.

Question, what does the sign "No engine brake...by city ordinance" mean on the highway? - Yahoo! Answers

When my Exhaust Brake is activated, you cannot tell the difference in the sound of the Exhaust at all.

Dr4Film ---- Richard
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Old 01-27-2013, 11:17 AM   #9
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More than just downshifting your transmission is happening as has been already stated. Diesels don't downshift and compression brake as well as a gas engine so the need some help. ( exhaust or engine brake) . Downshifting is used together with a device to retard the engine speed.
Just for fun , downshift your transmission manually , on the shift panel, and compare that to using the brake switch . I think you will notice the difference.
The trucks spoken of divert the exhaust without using the muffler .. That's the noise you hear , unmuffled exhaust. ( which by the way is becoming more and more illegal to use in communities and most commercial trucks no longer have those unmuffled devices . )
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Old 01-27-2013, 09:44 PM   #10
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The short answer is you do NOT have both engine and exhaust brakes. They are not used in conjunction with each other, though I suppose it is technically feasible to do.

Either one can be rigged to automatically downshift the tranny or to require that you do the downshifting yourself. That function is programmed into the ECM in modern diesels but can be turned off. But back in the old days, the driver always did it himself.
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Old 01-27-2013, 10:00 PM   #11
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Quote:
Originally Posted by crah View Post
An engine brake is far superior to an exhaust brake. 2 total different things and they both coordinate with the transmission. Not sure what exact engine you have but sounds like you have an exhaust brake. If you have a cummins isc or isb you will have and exhaust brake. A cummins isl can have and actual engine brake with a high low switch, and some isl models also have and exhaust brake. If your coach is the coachmen in your profile, you probably have an exhaust brake. I'm not certain on the cat engines but I'm sure others will chime in. Both will reduce brake usage but the engine brake being the better of the two.
Contrary to the above, an ISC can have an engine brake. I have a tag axle spartan and have a two position brake (low/high). Usually you are correct about ISB / ISCs having only an exhaust brake.
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Old 01-27-2013, 10:25 PM   #12
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The "No Engine Brake" signs are there because people don't like the noise that an engine brake makes. I guess they prefer to hear the noise that my coach makes when it crashes into their house?
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Old 01-28-2013, 04:59 AM   #13
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Just some info.:
Freightliners to have more Mercedes components,

Both series of engines provide engine braking, with an exhaust brake, a compression brake, or a combination exhaust/compression brake on the MBE900 and an exhaust/compression brake on the MBE4000. The MBE900 can generate up to 215 braking horsepower, while the heavy-duty MBE4000 is good for up to 500 braking hp.
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Old 01-29-2013, 04:56 PM   #14
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Just to offer more confusion they are telling me I have a turbo brake which its not an exhaust brake with a lever nor a compression brake.
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