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Old 11-24-2021, 08:32 AM   #1
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Allison 3000 shudder with engine brake

I have a 2005 Newmar MADP with the 400 ISL Cummins and Allison 3000. It has 38,000 miles. The 3000 shows no codes via the shift pad.

The engine brake has three settings - low, off, high.

When I use the engine brake, it works as it should except there is a "shudder" when the engine brake disengages at about 10 mph.

For example, if I exit the Interstate with the engine brake on low, it will slow the coach with the transmission eventually shifting into 2nd gear as the coach slows down. Once the coach slows down to about 10 mph, then engine brake seems to disengage and the coach shudders for a second or two. It does not shake - it shudders as if the transmission is shifting back and forth between gears or the torque converter is locking and unlocking.

Anyone have any idea what this is?
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Old 11-25-2021, 02:31 PM   #2
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Is this a new development or is the coach new to you? Yes the jake shuts off when approaching idle, otherwise it would kill the engine. So that much is normal. The shudder might just be perception as the driveline loses the load from the jake and torque converter unlocks at idle, unless its a new development. Also, have you tried coming to a stop without using the jake? If it happens either way, your torque converter might not be unlocking properly.
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Old 11-26-2021, 04:27 AM   #3
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It has been doing it for the 2.5 years I have owned the coach..

It does not do this without the engine brake.

It is quite pronounced. It is not a single hit. It is multiple hits over a second or two. It feels like I am running over rumble strips.

I have gotten to where I turn off the engine brake as I slow down to keep it from happening.
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Old 11-26-2021, 09:49 AM   #4
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Ok so not the trans. I’d say (guess) that your jake isnt cutting out early enough. For example, if its supposed to automatically cut out at 1000 rpm (typical), but it isn’t happening until 800, it would start to stall the engine. Since it may also have a speed based cut-off, with a speed sensor turning off the jake at around 15mph, that could be suspect too, but I think this is less likely.

You can check this by watching the tach as the issue occurs. This could be electronic (ECM adjustment) or more likely mechanical (Jake system service). There is a maintenance schedule but it starts at 100k miles, so yours has probably never been touched. But like so many other things, these maintenance schedules are intended for high milage vehicles based on use, not time, so the schedule may not be sufficient.

Either way a quick visit to a Cummins or Freightliner shop will likely fix it. My guess is you are manually compensating for whatever the issue is by shutting off the Jake when it should go off automatically.

https://www.jacobsvehiclesystems.com...s%20Manual.pdf

https://parts.jacobsvehiclesystems.c...ion-Manual.pdf
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