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Old 02-09-2016, 09:58 PM   #15
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The only thing I would add to the great advice above is as you are learning your coach, use caution at first. When you get to a long downhill that is signed 6% or so for several miles, slow right down at the start of the hill and let your Allison shift down to 3rd or so and get your exhaust brake working and see if it holds you back without having to use your brakes. If it slows you too much then you can go up a gear and it will probably hold you without using too much brake.
The advantage of doing this is that you don't heat up your brakes trying to get your speed right and on a long several mile downhill, it is easy to overheat your brakes to a point they won't work.
After you get used to your coach you will know what to expect from it.
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Old 02-10-2016, 06:05 AM   #16
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Even though I do not have a Two Stage Engine Brake but rather an upgraded PRXB Exhaust Brake, descending a steep grade with the engine brake is so much easier than with an exhaust brake.

Many of my friends who have engine brakes seldom have to use the service brakes when descending grades whereas with my nearly 24 tons of weight plummeting down a grade there aren't too many grades in North America where I don't have to use the service brakes to slow down my speed once it creeps up over 45 mph and before it reaches 54 mph. That's when my Allison up-shifts into 5th. If you let the tranny do that you will be in for a ride of your lifetime and will quickly get out of control.

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Old 02-10-2016, 06:26 AM   #17
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all good information...........I guess the thing to remember is, keep an eye on those behind you going down a hill, but don't let their "hurry" push you past your comfort level............I have seen many folks wind it up going down hill at speeds which to me seem out of control, just so they can make it up the next hill at close to the speed limit.......for them I say, good luck.........for me, I would rather feel comfortable going down a grade, even if it means a slow ride up the next hill.........
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Old 02-10-2016, 07:46 AM   #18
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as you approach the top of a grade, your current speed, when you take your foot of the pedal, will determine the speed that the exhaust brake tries to keep you at. In essence, you determine what speed you want the exhaust brake to hold you at as you start to descend a hill.

Yes, the grade will determine whether the exhaust brake can handle it, and the slower you top the grade the better it will work descending steeper grades.

Also, if you use cruise control, the exhaust brake will also work to help maintain that general speed if you are descending a hill, but it will not slow you as well as with the cruise control off.

You will also, at times, need to apply some manual brake pressure, especially on longer steeper grades. As you apply pressure and start to slow, the exhaust brake will help reduce your speed even more.

Note: some will keep the exhaust brake switch on at all times. I use it only when needed. No need for it when on flat roads or when I want to let off the pedal and allow the coach to roll on it's on, such as at slower speds and in light traffic. I do use it when in heavy stop-and-go traffic and on mountain descents, of course.
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Old 02-10-2016, 09:17 AM   #19
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Adding to the excellent answers so far...
Downshifting by itself does nothing on a diesel because there is no inherent engine resistance (braking), so your choice is really only "both", with the gear chosen controlling the amount of braking effect you get. Your coach will automatically downshift on a downgrade as long as the engine or exhaust brake is turned on. Just take your foot off the go-pedal. Mine targets 4th gear, but some are set up for 2nd instead. It won't actually achieve that gear until the speed is low enough to safely do so, but the tranny is working toward that. You will feel it shift as it does. Use the brake pedal as needed to help out.
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Old 02-10-2016, 09:34 AM   #20
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Originally Posted by Gary RVRoamer View Post
Adding to the excellent answers so far...
Downshifting by itself does nothing on a diesel because there is no inherent engine resistance (braking), so your choice is really only "both", with the gear chosen controlling the amount of braking effect you get. Your coach will automatically downshift on a downgrade as long as the engine or exhaust brake is turned on. Just take your foot off the go-pedal. Mine targets 4th gear, but some are set up for 2nd instead. It won't actually achieve that gear until the speed is low enough to safely do so, but the tranny is working toward that. You will feel it shift as it does. Use the brake pedal as needed to help out.
Really? I have been doing it wrong? All the signs that read "Trucks use lower gears" are misleading? A Diesel Engine does provide "Brake Horse Power" when down shifting (even with an Automatic) I read the comments on how to maintain down grade speed with a 40,000 lb Coach and get the feeling it's more of a chore to do than a Quarter Million pound Truck n Trailer with a Heavy piece of Equipment! That can be rolled down the Baker Grade and any other long/steep grade I go down without touching the brake pedal, "stabbing" the brakes would heat them up in a big hurry as opposed to holding a steady 5#'s of pedal pressure (basically resting your foot on the pedal) ..Exhaust Brake, correct your speed at 5mph over with light pedal pressure NOT STABBING! (Your comfortable down hill speed corrected @ 5 mph over) 50 + 5, at 55 lite brake pressure till 50, repeat......
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Old 02-10-2016, 09:46 AM   #21
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I will add this about the exhaust brake, its more effective at higher rpm. I just bought a new Phaeton and at first i didnt think it held the speed going downhill as well as my Red. Its actually not the case as it does hold but at different speeds than the Red would. If you feel it isnt holding you back without the brakes then slow down enough that it shifts down and let the rpm's go higher and i believe you will find a comfortable speed.
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Old 02-10-2016, 10:26 AM   #22
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Originally Posted by DMTTRANSPORT View Post

I have to ask what this is??
Another common term used is Snub Braking.

Here a YouTube video showing how to accomplish the task.

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Old 02-10-2016, 10:30 AM   #23
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Another common term used is Snub Braking.

Here a YouTube video showing how to accomplish the task.

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Old 02-10-2016, 09:36 PM   #24
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Although similar there is a difference between stab braking and snub braking. Stab braking is forcefully applying the brakes to lock-up then releasing them. Snub braking is firmly applying the brakes to reduce speed to your target speed.
You should use one gear lower to descend than you did to climb the grade.
Source: CDL practice test
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Old 02-10-2016, 10:17 PM   #25
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Might be just me but on some gentle downgrades the exhaust brake slows to much but selecting a lower gear does seem to hold the speed down a bit. But for most down hill runs the exhaust brake is what I use,
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Old 02-10-2016, 10:43 PM   #26
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Downshift or Exhaust Brake

I am surprised in this discussion that there are several references to risks of overheating of the brakes but no mention of running low on air supply by frequent applications of the brakes.

When I took the air brakes course, the instructor stressed holding a steady pressure on the brakes (as DMTTRANSPORT mentioned) as opposed to frequent short brake applications to control the speed, since each application and release eats up air supply. He maintained that the brakes will not overheat if a steady pressure is used to keep the speed under control.

I think paying attention to one's air supply should also be mentioned in this discussion.
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Old 02-10-2016, 10:55 PM   #27
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With the present rig I haven't found a grade yet that required me to touch the brakes to keep the rig slowed down. But most don't have a three stage engine brake with up to 600hp of retarding either.
With the previous Dutch Star having just an exhaust brake I did have to "snub" brake to keep it slowed at times. WA CDL test manuals say not to ride the brakes as they can overheat.
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Old 02-10-2016, 11:01 PM   #28
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Quote:
Originally Posted by Ray,IN View Post
You should use one gear lower to descend than you did to climb the grade.
Source: CDL practice test
I've probably read this tidbit of advice a hundred times on this forum and always wondered, what if you've never climbed this grade !
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