Coast Resorts Open Roads Forum: Class A Motorhomes: EXHAUST BRAKE PROBLEM
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 > EXHAUST BRAKE PROBLEM

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FRIZBEE1

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Posted: 12/20/13 11:34am Link  |  Quote  |  Print  |  Notify Moderator

Specs: Monaco 03 Windsor, Cummins 370 ISL engine, Allison 3000 Trany.
The exhaust process as I understand it. 1. Brake switch on. 2> Foot off throttle. 3. Tranny downshifts to a preset range. 4. Exhaust brake engages.
What happens 1. Everything works normal. 2. Tranny downshifts but exhaust brake won't engage. 3. Nothing happens.
What we know: Exhaust brake tests good and is lubed.

Pending: Suicide if I can't get this fixed. DW won't go camping until I do.

ScottG

Bothell Wa.

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Posted: 12/20/13 11:44am Link  |  Quote  |  Print  |  Notify Moderator

So the EB turns on at idle if you engage it?


Scott, Grace and Wesly
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mtrumpet

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Posted: 12/20/13 11:51am Link  |  Quote  |  Print  |  Notify Moderator

This same exact thing happened to me a couple of years ago. It turned out to be a bad Exhaust Brake Switch. Replaced the switch with a new one from Newmar, and problem solved. At Spartans' suggestion, I checked it by removing the switch and jumping the wires (bypassing the switch). The exhaust brake then worked fine, proving the bad switch.

You can certainly run without the exhaust brake. Just make use of manually downshifting with the arrow keys on your tranny when needed. Not as efficent as the exhaust brake of course and will require more attention to rpm's and speed, but it can be used to assist with slowing the coach. You won't hurt anything (the tranny computer won't allow it.) Heck, trucks had run for years without engine brakes.

When mine went out, I was a couple of hundred miles from home. No big deal. In fact, when I took my road test for my "R endorsement", I wasn't even allowed to have the exhaust brake turned on.


Mark & Cherie
2002 Newmar Dutch Star DP 3872, Cummins 350 ISC, Spartan Chassis
2003 Ford Explorer, Blue Ox Aventa Tow Bar w/ Ready Brake & Ready Stop


mtrumpet

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Posted: 12/20/13 12:01pm Link  |  Quote  |  Print  |  Notify Moderator

FRIZBEE1 wrote:

What happens 1. Everything works normal. 2. Tranny downshifts but exhaust brake won't engage. 3. Nothing happens.


Just to clarify, are you saying that the number on the Tranny control indicates the target gear? (I believe that most are defaulted to "2"). If yes, then the problem could be more than a bad switch. When my switch went bad, the tranny control wouldn't even indicate the downshift gear. It was just as if the exhaust brake was turned off.

FRIZBEE1

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Posted: 12/20/13 12:01pm Link  |  Quote  |  Print  |  Notify Moderator

Scott, Brake won't engage at idle.

JimM68

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Posted: 12/20/13 12:04pm Link  |  Quote  |  Print  |  Notify Moderator

need more info.

exhaust brake switch on, foot off gas, trans selector should immediately indiate 2?

RPM permitting, trans should downshift, bringing rpm up to perhaps even near 3000?

Exhaust brake should close, further slowing motorhome.

What makes you think this isn't happening?


Jim M.
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FRIZBEE1

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Posted: 12/20/13 12:22pm Link  |  Quote  |  Print  |  Notify Moderator

Mtrumpet, Under what happens, 1. trans light goes to 4. 2 Trans lite goes to 4. 3 trans lite doesn't change and stays at 6.

FRIZBEE1

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Posted: 12/20/13 12:24pm Link  |  Quote  |  Print  |  Notify Moderator

JimM68. When the two functions take place, I can feel each one.

wolfe10

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Posted: 12/20/13 12:30pm Link  |  Quote  |  Print  |  Notify Moderator

Since the transmission is downshifting normally, the circuit is fine all the way to the transmission, From there the electrical signal at the air solenoid needs to be checked. Set up a test light or voltmeter so that someone can see it while you drive.

If the light/voltmeter indicates the solenoid is getting 12 VDC when the brake engages. then you know you have a mechanical issue with air cylinder or exhaust brake. If not, you need to get the schematic and find out between Allison ECM and exhaust brake solenoid where the signal is lost.


Brett Wolfe
2003 Alpine 38'


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FRIZBEE1

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Posted: 12/20/13 12:53pm Link  |  Quote  |  Print  |  Notify Moderator

wolf10 In the number 3 scenario the tranny does not downshift, which still leaves open the throttle break switch as a possible culprit. That what makes this thing so confusing.

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