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Old 05-26-2011, 02:57 PM   #1
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Engine Brake

Ok I am a newbie My rig has the Hi/ Low brake switch, I understand ( maybe) low is on the bottom of the switch and that use 3 cylinders and High uses 6? or am I backwards

Also when do I use high and low when or what grade I have some 6 and 8 % grades to come down on my Maiden voyage
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Old 05-26-2011, 03:57 PM   #2
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Hi jhalldiver,
Low will make the transmission search for a higher gear than the Hi setting which, I think, is a standard 2nd gear search target.

Unfortunately, there is no standard answer. Descend a grade at a safe speed you are comfortable with. The objective is to use the coach service brake as little as possible. Let the engine brake to the work.

If the coach continues to gain speed and the service brake needs to be used, consider "stabbing" the service brake (like in the Hitchcock movie). This will slow the coach quickly without heating up the service brakes.

For me, I descend grades at different speeds depending on all the usual factors. My exhaust brake will hold my combined 37K lbs of weight at 55 MPH on a 7% grade. Sometimes this is okay and sometimes not okay. If not okay, I stab the service brake to get the coach to the speed I am comfortable at. Then wait to see if the coach holds or I need to stab the service brake again, further down the grade.
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Old 05-26-2011, 04:24 PM   #3
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Hi/Low

So do you you have your switch set in high or low for steep grades?
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Old 05-26-2011, 04:26 PM   #4
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It would help if you created a signature in your profile which outlined for all of us what kind of rig you have. You'll probably get more precise answers to your questions in the future.

Excellent advice from Gary on all counts IMHO... except on our Allison 3000 six speed both the low and high brake settings try to seek downshifts to 2nd gear but that is all programable. I love my engine brake and if the truth be known it was a big reason I bought a diesel. I was far more concerned with being able to stop a big rig than to get it moving faster!

Good luck...

Rick
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Old 05-26-2011, 04:44 PM   #5
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Need to know if it's an exhaust brake or a Jake brake. I've seen both with a low/high switch. On most with exhaust brake, low setting is exhaust brake only and the high setting is both exhaust & tranny downshifting to the programmed low gear. On the jake it's what you said in your first post; low is 3 cylinders and high is all 6.

Also many ways to program what / how it’s working. When I re-program mine, I will change the low setting so the tranny is downshifting, but only trying to get to 4th and will also change the mode setting parameters to better suite my driving style and for towing the race trailer.

Now for what to start with in a new / used coach, well I always start with high and if that’s too much then kick it to low….
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Old 05-26-2011, 05:08 PM   #6
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I have the 400 ISL with an engine compression brake (jake brake) and I have found that in the low position the brake will hold 55 mph on a 6% grade. More than a 6% grade and I use the high position and it is generally good up to an 8% grade. I can usually handle these grades with little or no use of the service brake. I love it. It has really given me a lot of confidence in handling mountain driving
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Old 05-26-2011, 05:54 PM   #7
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The High/Low switch on an engine compression brake (Jake Brake)controls how many cylinders are used for compression braking. In Low you only use 3 cylinders and in High you use all six cylinders. I leave mine in High most of the time and use it instead of the service brakes just to save wear on my brakes. Both High and Low modes will reprogram the Allison transmission but High is a lot more aggressive. Be very carefully if you get above around 68-70 mph because the MPH is too fast for the transmission to downshift. You will still get compression braking but it will not be as aggressive. A helpful hint here is never use the Jake brake on a cold engine because the oil pressure is too high and the oil is too thick. It uses the oil to control the compression brake. I don't find too much use for the Low mode.

A warning here because the engine compression brake only applies braking to the rear wheels then on a slick road in the rain it is possible to apply too much braking to the rear wheels and cause the MH to skid sideways. It is a real scary feeling but releasing the Jake brake will straignten it right back out again. If it is raining then I use the service brakes in conjunction with the Jake Brake.

For emergency stopping on the road I will use both the service brakes and the Jake Brake. It will slow the rig down real fast.
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Old 05-26-2011, 06:44 PM   #8
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We should also point out that using a Jake Brake on slick roads can be a good way to meet the rear end of your coach as it passes you by. I think it's pretty frowned upon.

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Old 05-27-2011, 12:07 PM   #9
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Engine Brake

Thanks guys I feel a lot better. More info is better.
We purchased a new to us 2006 National Tradewinds 40D 11,000 niles 400hp. Our toad is a 2009 Jeep Wrangler.
We pick it up Monday and will make our maiden voyage pulling the Jeep back home through the mountains. When test driving the coach i tried the engine brake and found the high setting to be very agressive. I was told by an old trucker to never come down the mountain faster than I went up and I would be fine. I am use to pulling our fiver but the coach is new to us.

This is a great forum and I have learned a lot from all of you. Hopefully I will be able to contribute someday.

Thanks
Jack
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Old 05-27-2011, 12:23 PM   #10
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Quote:
Originally Posted by jhalldiver View Post
When test driving the coach i tried the engine brake and found the high setting to be very agressive. I was told by an old trucker to never come down the mountain faster than I went up and I would be fine. I am use to pulling our fiver but the coach is new to us.

Thanks
Jack
Congrats on the new rig.

That old trucker gave you some good advice. It's generally felt that you should also descend a hill in the same gear you use to go up it but use of the engine brake takes that out of your hands. I work hard to stay ahead of the game when descending big hills. Once you find out you're going faster than you want to... you could already be in trouble.

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Old 05-27-2011, 01:00 PM   #11
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Hi jhalldiver,
My exhaust brake has only an on or off. Only one setting and that is on.
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Old 05-28-2011, 09:25 AM   #12
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The Jake brake on my 400 ISL is wired backwards from the norm - Lo brakes with 6 cylinders and Hi brakes with 3 cylinders. I could probably switch the wires on the switch, but as long as I know which is which I don't really care. I run in the 3 cylinder mode all the time and only select 6 cylinder braking on long, extreme grades, maybe 6% and up.
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Old 05-28-2011, 10:06 AM   #13
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Congrats on the new rig. As others have said, they can all be a bit different. You will just need to go for a test drive and get a 'feel' for what your coach does.

In general, my way of doing this, with a 2 stage Jake:
-I usually leave it off in normal highway riding, as Wolfe says on RV.Net, it's that coasting that gives me my best MPG!
-When in city highway traffic, I use low stage, to help me in stop and go traffic. I also set our US Gear Toad to a 7 position, in case of emergency stops.
-On rolling down hills LT 6%, where 55mph is safe. I use the brakes to slow down to 55, then kick in the low stage.
-On GT 6%, or in twisty 45MPH or less speeds, I slow down to 45-50MPH, as appropriate, then engage high stage. Also using the service brakes as needed, if slower curves or speed builds up.
-Our Country Coach, ISL, currently has high go to 4th gear. As needed, I'll down shift lower. (As mentioned, watch your speed in relation to the gear you choose. Most times the computer between engine and trans, will not let you hurt them. But, I try to be sure the gear and speed keeps the RPM below the top end.)
-Also check you rig on Cruise Control with Jake. Our Jake will not engage, while in Cruise Control.
-When in doubt, go slower then you think is needed, until you get a real good feel for your trans/jake low & high/service brake combination.
-When I know I have heavy mountains up/down on a course. I keep the fuel planning a tanks of water/grey/black as low as I feel I can. (If boondocking, and no place to fill water, makes a difference. But when on the road, and hitting parks most nights, we travel with about 1/4 -1/3 water.) Each rig's fuel tanks and MPG is different, but with ours, I'll try to plan a 1/3-2/3 fuel tank or less, depending upon distance to be traveled the for that day. (This is all after learning your rig, and I never take a chance of dropping below 1/4 during a trip. I also get my fuel level to where I want it Full (or less if mountain driving) at the end of my day travel. Ready to head out in the AM.

Relax, enjoy learning all the new things in your rig, have fun,
Smitty
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Old 05-28-2011, 11:48 AM   #14
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Smitty, your Jake is not on a foot pedal control? Mine is and I leave it turned on in high all the time incase I have to slow down or emergency stop on the highway. This saves wear and tear on the service brakes plus slows you down faster in an emegency stop. I can program the engine ECU to engage it when I let up on the accelerator but I feel I have more control with a foot switch. Trucks use the let up on the accelerator to engage it because they only have two feet and three pedals and can't work another pedal. Mine doesn't work from the foot pedal if the cruise control is on either but if the VORAD radar senses a high closure rate to a slow or stopped object then it will apply the Jake brake even in cruise control.
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