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Old 02-25-2013, 11:08 AM   #1
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Engine braking vs. exhaust braking

Planning a trip to Alaska this summer. We are going to start from south Texas and head west, hugging the west coast on the way up, veering off to see Yellowstone and other NP's. expecting some steep grades. We don't know ( because we are newbies ) if we need a exhaust braking system, or if engine braking in combination with pedal braking.
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Old 02-25-2013, 11:15 AM   #2
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If you have an engine brake you don't need an exhaust brake.

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Old 02-25-2013, 11:21 AM   #3
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Do you have a gasoline or diesel engine? If it's a diesel, what make and model (some use exhaust brakes; others use engine brakes).

On edit - looking at your profile, you have a 2003 Tiffin Phaeton 38', so it looks like a diesel. What engine do you have in your coach?

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Old 02-25-2013, 11:26 AM   #4
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What engine do you have? Engine brakes are not made for all diesel engines. Exhaust brakes like the Pacbrake PRXB are available for almost all. The exhaust brake is far more commonly used. We have a PRXB on our C-7 Cat and it works quite well.

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Old 02-25-2013, 01:24 PM   #5
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I use my exhaust brake on long hills,MH's with air brakes are like big trucks they can over heat that's why they have runaway truck sand piles.
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Old 02-25-2013, 02:27 PM   #6
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We have been to Yellowstone with our RV and, indeed, there are some "interesting" grades. Here are some recommendations.

1. Consider buying the Mountain Directory West and using it help you with your trip. It is a book which provides data by State. It highlights most of the steep roads and provides details about them. It is somewhat conservative in its assessments.
2. Interstates are limited to 6-7% grades which, with proper driving technique, are fairly easily managed. Other roads can be 8,9,10 percent. The couple of 10% grades that we've been on (one in NC, the other at Palo Duro Canyon in Texas) require very careful driving. Simply having an exhaust/engine brake isn't enough.
3. The idea on decent is to maintain "equilibrium", meaning that the vehicle is not constantly picking up speed. Short stabs of the service brakes (with the pedal) are used to stop the speed build up. People standing on the service brake pedal for long periods of time can be the cause for burnout and runaway conditions. At first, I practiced with ours on every small hill that we have here in Texas, trying to get a feel for how to do that. You don't want your first experience to be on an 8% plus grade, especially a twisty one.

As RustyJC suggests, your engine already has one of the two types installed. Most of the smaller diesels like our 5.9 Cummins do not have an engine brake option. Even though the console button says "engine brake" or, in our case "retarder", it still may be an exhaust brake. If it is, it should be a visible device mounted just after the engine's exhaust manifold.

The exhaust brake is simply a butterfly valve in the exhaust which helps to create some engine backpressure. Ours has a limited effect on the engine. The engine controller and the transmission controller work together to activate the exhaust brake but are set up to prevent the engine from being destroyed. On one 10% grade, our transmission upshifted (in spite of the fact that I locked it into low gear) when I didn't manage the equilibrium correctly and the engine was in danger of being over-reved. It was a scary moment.

Engine brakes are more robust and many of them have two different levels. They are used in the largest diesels when the coach is quite heavy. We were in one of the huge tow trucks after a rental RV broke down on us when the driver kicked on the engine brake. The affect was really amazing, especially considering the size of that truck and our rental RV that he was towing.
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Old 02-25-2013, 03:06 PM   #7
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A couple of small additions. The transmission upshift 11 experienced was a normal function that prevents the engine from overspeeding. When it happens no damage has been done and when you slow it will return to the lower gear it was in. My C-7 Cat will do that if the rpm reaches 2650 rpm down hill with the exhaust brake on.

The exhaust brake will be mounted to the outlet of the turbocharger.

If your coach is what someone posted it is very likely it HAS a exhaust brake.

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Old 02-25-2013, 03:36 PM   #8
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A cat. 330 hp diesel
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Old 02-25-2013, 03:46 PM   #9
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Not sure of the model as I bought it 2nd hand. And this is probably going to sound like a really stupid question. But here goes,is that what RTDR switch is and if so how and when should I use it? Try not to laugh... Just trying to learn, and all of y'all have been an enormous help, thanks so much for any other info on this.
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Old 02-25-2013, 04:50 PM   #10
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Quote:
Originally Posted by lmurraytwst View Post
A cat. 330 hp diesel
You have an exhaust brake. There is a main switch which will turn the system 'on', and it can be labeled engine/exhaust/retarder brake.

There are many posts on this forum regarding the use of exhaust brakes. They work very well slowing the coach, in conjunction with the engine rpm's. That's why the unit will generally downshift into a lower gear when the exhaust brake is called for.

Good news is that the engine/transmission/exhaust brake are computer controlled, and you can't hurt the system. It won't let you.
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Old 02-25-2013, 06:18 PM   #11
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Quote:
Originally Posted by lmurraytwst
Not sure of the model as I bought it 2nd hand. And this is probably going to sound like a really stupid question. But here goes,is that what RTDR switch is and if so how and when should I use it? Try not to laugh... Just trying to learn, and all of y'all have been an enormous help, thanks so much for any other info on this.
More than likely the RTDR is short for "retarder" and is the off/on switch for the exhaust brake. I believe your Tiffin has a Cat C7 or perhaps 3126 depending on when the engine was produced. Either way the small Cat has an exhaust brake. There are many, many opinions about the best way to use the brake. I my opinion, the only down side to leaving the brake switch on all the time is the effect the brake has on the cruise control. The way the exhaust brake is usually controlled by the engine ECM, if you start down a grade with the cruise on and you start picking up speed because of the down grade, when the cruise closes the throttle, the exhaust brake will activate and select 2nd or 3rd gear and start slowing the coach. You may want this but you might prefer to coast down grade ( especially if a short down followed by an up grade).

Since you are learning, I would start by leaving the exhaust brake on all the time and get accustomed to its operation. You will learn in good time what suits your driving style.
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Old 02-25-2013, 06:46 PM   #12
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When you start playing with your exhaust brake you will find at times it is kind of jerky when you let all the way off of the throttle applying more brake than you want especially at lower speeds in traffic. You can play with the throttle and you will find a spot just before the throttle pedal is all the way off where the power will be clear off but the exhaust brake will not engage. It is a narrow spot but when you figure it out you will find its handy.

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Old 02-25-2013, 07:15 PM   #13
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"Retarder" might also refer to the Allison Retarder, which is part of the transmission but accomplishes the same result as an engine or exhaust brake.
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Old 02-25-2013, 07:38 PM   #14
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"Retarder" might also refer to the Allison Retarder, which is part of the transmission but accomplishes the same result as an engine or exhaust brake.
This is true, but there is absolutely no chance that the OP's Tiffin has an Allison retarder. Foretravel is the only builder I'm aware of who use the transmission retarder.
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