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Old 01-22-2018, 08:45 AM   #1
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400 hp cummins exhaust brake

New to forum, but not new to questions. We recently purchased a 2006 Newmar Dutch star 4320 with Allison 3000mh transmission and 400 ISL Cummins. Before buying,(I bought long distance) I had the unit surveyed. Usual problems for year of coach, most of which have been simple fixes. My question concerns engine break. I had salesmen sent photos of cockpit switches. There is a switch labeled engine break,so I assumed it was an engine break(compression). While driving home from Florida to MA, I had opportunity to go through some hilly terrain, as I avoided the major cities by going west of them. Having read up on the two types(exhaust and compression) I assumed I had an engine brake not an exhaust break. Not! The coach has almost 0 bhp. Several times it was like a runaway train coming down hill. I had to stand on the brakes more than once to the point of smelling brake linings hot. Speed was around 55mph but picking up. So I tried manually down shifting, to now avail, as transmission will only do so as programmed. I have read that some Allisons show something that says it is in a downshifting mode. But as far as retarding power I felt none and still don't now. I have to rely solely on service breaks for all slowing and stoping. Does anyone know what I'm not doing correctly? Or know something I don't? Would love some auxiliary braking. I know Cummins changed to real compression breaks in 07, with two stage buttons, hi and lo. Love to hear opinions.
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Old 01-22-2018, 09:04 AM   #2
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I have a 2004 Damon on a 2003 Freightliner chassis with the Cummins 400 ISL and I can tell you that I have a two-stage compression brake... so there are units pre 2007 with this feature.

I have noticed that, when cruise control is on, it can begin to run away going down hill... but tapping the service brakes would kick out the cruise and allow the engine brake to operate. Why yours wouldn't points to, maybe, a malfunction?
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Old 01-22-2018, 09:08 AM   #3
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Glad to have you here in the forum with us. You're gonna like it here.

Regardless of whether you have a compression or exhaust brake you should have felt it retarding your MH. On my DS, although I have a CAT, I simply activate the switch and the brake applies. Sounds like yours is not activating. Someone else may have another opinion.

Happy Trails!!!
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Old 01-22-2018, 09:10 AM   #4
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Is the Engine Brake switch a rocker 3 position, or a single position?
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Old 01-22-2018, 09:21 AM   #5
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My 2005 Itasca has a very similar set up. I have the same engine and transmission as you do. My switch has 3 positions of Off, Low, & High. My engine brake (Jake brake) works very well. I leave mine in the Low setting all the time while driving. The High is too aggressive even going down a steep grade I have to hit the accelerator. When in speed control the brake does not kick in until I go more than 7 MPH over the setting. To kick it in sooner as blang has stated just hit the brake peddle.

My suggestion is to make sure your switch is set where you need it to be. Assuming you have a Freightliner Chassis you can call the 24/7 help line and ask what they think can be wrong. In case you don't have it the number is 800-385-4357. I hope you get your problem resolved.

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Old 01-22-2018, 09:36 AM   #6
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I did not mention it is a Spartan MM chassis. Perhaps there is somethin wrong between switch and engine relay or some such.
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Old 01-22-2018, 09:37 AM   #7
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Single postion. ON or OFF
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Old 01-22-2018, 10:06 AM   #8
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Welcome to the forum.

You may have an actual exhaust brake that needs lubing.

Exhaust and Engine Brakes | Tune-Up Kits & Solenoids | Pacbrake
I searched for my exhaust brake on my 2008 ISL and found none. It turns out it has a variable ratio turbo that does the job.

Since you are new to the forum I want to share a very good tool to help you find even more answers.

I am not trying to keep you from posting any questions. Just want to share a great search feature I just used to find that web page for you.

Type bits of your question into the little green search box and you will find tons of information that comes from this forum.
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Old 01-22-2018, 10:09 AM   #9
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Quote:
Originally Posted by maxdog View Post
New to forum, but not new to questions. We recently purchased a 2006 Newmar Dutch star 4320 with Allison 3000mh transmission and 400 ISL Cummins. Before buying,(I bought long distance) I had the unit surveyed. Usual problems for year of coach, most of which have been simple fixes. My question concerns engine break. I had salesmen sent photos of cockpit switches. There is a switch labeled engine break,so I assumed it was an engine break(compression). While driving home from Florida to MA, I had opportunity to go through some hilly terrain, as I avoided the major cities by going west of them. Having read up on the two types(exhaust and compression) I assumed I had an engine brake not an exhaust break. Not! The coach has almost 0 bhp. Several times it was like a runaway train coming down hill. I had to stand on the brakes more than once to the point of smelling brake linings hot. Speed was around 55mph but picking up. So I tried manually down shifting, to now avail, as transmission will only do so as programmed. I have read that some Allisons show something that says it is in a downshifting mode. But as far as retarding power I felt none and still don't now. I have to rely solely on service breaks for all slowing and stoping. Does anyone know what I'm not doing correctly? Or know something I don't? Would love some auxiliary braking. I know Cummins changed to real compression breaks in 07, with two stage buttons, hi and lo. Love to hear opinions.
It sounds like you have two problems with the information from your thread. First is that your exhaust or engine Jake brake is not working. Second is that you cannot manually downshift from the key pad. Even with the engine brake not working you should be able to down shift the transmission at the top of the high and manage the speed with occasional use of the brakes. Have you tried to shift or select a gear while travelling with the engine brake off? This will sort out if the key pad is working properly. Also if you are trying to downshift at too high a speed the transmission will protect the engine from over revving. I would suggest conservative driving until your DP is repaired. Using of the service brakes excessively will lead to brake fade and or no brakes. Best of luck with your new coach. It is an up hill battle trying to figure and feel out.
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Old 01-22-2018, 10:42 AM   #10
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Your manual should have a section on how to operate the engine or exhaust brake. I suspect there should be a light come on the dash when the brake engages (does it come on ?) . You might check for a blown fuse...the manual should give a clue .
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Old 01-22-2018, 11:24 AM   #11
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Single postion. ON or OFF


Single position on/off is an exhaust brake. PAC brake is one manufacturer but there are others including Jacobs which leads to confusion. Also could be the VG turbo but I think that configuration came later. Many manufacturers used the exhaust or compression brake as an up grade point between coaches. I would guess that Newmar used the ISL in the Mountainaire and equipped it with a compression brake.

Sounds like your exhaust brake isnít working.
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Old 01-22-2018, 11:26 AM   #12
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I haven't tried downshifting without engine brake switch off. I'm aware of high shift points, and may try braking to high point threshold, and working my way down as needed. I only wish I had made sure that it was indeed a compression brake. I think Newmar should have labeled it an "exhaust" brake, not engine brake on rocker switch.
The next move is to take to cummins dealer and get to bottom of this.
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Old 01-22-2018, 11:44 AM   #13
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Did you notice when activating the exhaust brake switch, the allison keypad 'Gear selected' number go down to maybe 2, or 3rd gear? The two numbers on the keypad are gear selected, and current gear you are in.
Like a previous poster mentioned, if your RPM's are to high, your tranny wont drop a gear.
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Old 01-22-2018, 12:13 PM   #14
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I have the single window transmission plate. No matter which position the engine brake switch is in, shifter never shows anything other than 6, unless I manually downshift.
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