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Old 08-09-2016, 06:28 PM   #1
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Spartan Chassis
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Engine Brake triggers Brake Controller

2005 MADP 4301 towing trailer with electric brakes. I noticed that when the engine brake kicks in the lights on my brake controller light up indicating trailer brakes are activated. Looking at the wiring diagrams, it appears that both the service brakes and the engine brake connect to a single solenoid to turn on the brake lights. This is a good thing because we want the brake lights to come on when the motorhome is slowing down. However, when just using the engine brake, it looks like the signal backfeeds to the brake pedal where the brake controller for the trailer gets its signal. I spoke to Newmar support who said I should not turn on the engine brake unless I was driving in the mountains....else the motorhome brake shoes would glaze from under use. However, my concern is that on a long downgrade in the mountains with the engine brake on, this will result in burning up my trailer brakes. Any ideas ?

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Old 08-09-2016, 06:35 PM   #2
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Since you're not using the engine brake to come to a complete stop, just to slow down, you could disable the engine brake from sending any signal to the brake light solenoid at all. If you're planning to reduce speed even more, you'd press on the brake treadle and turn on the brake lights and the electric brakes on the trailer. If you observe someone behind you coming up fast, again tap the brake treadle to signal them.


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Old 08-10-2016, 08:13 AM   #3
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I like your suggestion - this would be similar to slowing down a motorcycle using the engine...tap the brakes to let following drivers know you are slowing.

I am not a mechanic nor an electrician, but I think the wiring diagram shows that the backfeed from the engine brake where it attaches to the stop light solenoid, also backfeeds via a split in the circuit between the pedal and the stoplight to a solenoid labelled "Service Brake Status" . I am reluctant to just disconnect the engine brake wire from the stoplight solenoid because the backfeed to the"Service Brake Status" might be important.

The Newmar service person I talked to said it was by design that the engine brake turned on the stoplight. He suggested a "converter package" to modify the brake controller to recognize if the signal was coming from the engine brake or the service brake. Ever heard of this ?

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Old 08-10-2016, 08:27 AM   #4
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Could you connect your controller between the service brakes and relay and install a diode so the engine brake signal couldn't back feed into your controller.
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Old 08-10-2016, 08:37 AM   #5
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Never heard of any "converter" that can tell where the 12v on the brake light circuit originated. How could it know the difference?

Back in the day, exhaust and engine brakes never turned on the brake lights. That was an "good idea" that came along later, to signal that the coach is slowing. As far as service brake status is concerned, I think that is not a concern. The engine brake is NOT the service brake and in fact should NOT alter the status. In fact, I think there should be a diode that prevents the engine brake signal from backfeeding to it.

However, assuming your trailer brake controller is proportional, I think you are worrying over a trivial thing. The trailer brakes should only be lightly applied with the amount of braking the engine brake does, and you can still pump the service brake if you want to vary the braking pressure.
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Old 08-10-2016, 09:46 AM   #6
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I just recently purchased the MADP ....previously owned an Itasca Suncruiser with a Ford V10. First trip I took with the trailer I stopped at a Tim Horton's (Canadian thing ,,, eh!) and the trailer brakes were very very hot. I had only gone about 20 km but it was mostly down hill and I was running with the engine brake on low setting (at the recommendation of my trucker friends). The tires were not scuffed so it appears that the brakes were partially on ? I went back home (mostly up hill) and the brakes were cool. However on examining them, they were fried and I replaced them. I don't want to repeat this.

The Newmar service recommendation to not use the engine brake except when in the mountains will help but probably not solve the problem.

The brake controller is of the "timed" type...not "proportional". So maybe switching to proportional would help as suggested by Gary.

There is a diode on the engine brake side of the stoplight solenoid to prevent feedback from the pedal to the engine brake circuits. However I don't see any diode on the pedal side of that solenoid to prevent feedback from the engine brake...installing one as suggested by Bamarider might be a better solution.

Thanks for the input,
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Old 08-10-2016, 10:45 AM   #7
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Everything should be fine the way it is. Just because the brake controller is activated does not mean the brakes are. A brake controller has a decelerometer in it that measures how much you are slowing down (negative g force)and that controls the current sent to the brakes. If the engine brake is just keeping you at a constant speed and not slowing you no current will go to the brakes
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Old 08-10-2016, 10:47 AM   #8
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I had the same thing . Cut the wire coming from the engine brake. The wire is behind the fuses in the front box driver side. It goes to the stop light relay, it is mark.
2005 madp m4030
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Old 08-10-2016, 02:16 PM   #9
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Good input. Based on the comments, I will temporarily disable the engine brake from talking to the stoplight solenoid. This is a 5 second fix because the connection is visible in the DILL block in the Power Distribution Centre at the front of the coach on the drivers side. The only downside I think is that the Brake lights won't come on when the Engine brake comes on.
Longer term, I see two options:
1. Trade in my "timed" brake controller for a "proportional" one.
2. Add in a diode to prevent the engine brake from backfeeding the circuit where the brake controller is connected.

As for when to use the engine brake, clearly descending long grades would be the primary use. However I also found it quite useful in heavy see-saw (fast slow) traffic coming across the top of Toronto.....in fact, I didn't need to touch the service brakes at all because the traffic never came to a full stop. Still thinking about that.

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Old 08-10-2016, 02:36 PM   #10
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Who installed the brake controller and why was it installed the way it is? Sounds to me like the person wiring in the brake controller did not know what they were doing.

I installed my Prodigy P3 Brake Controller to use when towing my cargo trailer.

I also use my exhaust brake all the time when needed therefore the exhaust brake switch is on all the time which means that I don't have to think about turning it on or searching for the switch with my left hand.

Also, my brakes lights are activated when my exhaust brake is working. They are off when I am coasting or accelerating. However, the Prodigy does not activate when the exhaust brake is working. It will only activate when I step on the brake.

That is how your braking system should work!

Dr4Film ----- Richard
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Old 08-10-2016, 05:39 PM   #11
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This is not a unusual problem US brake sells a Diode that you put between the brake light wires and the retarder igniter wire. This allows the retarder to work and the light to come on without sending a signal to the brake controller. I use this and it works great.
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Old 08-10-2016, 05:45 PM   #12
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I think you lucked out with the Spartan Chassis because you can disable it by fuse even. I haven't found a way on the Freightliner yet. I really don't like my brake lights coming on with the exhaust brake. I just know I'm giving the guy behind me a surprise when I actually use the brakes and he probably cusses.

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