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Old 04-20-2011, 07:13 PM   #1
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Join Date: Feb 2011
Location: Santa Clara, CA.
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Cummins ISB 340. Allison 2500MH. RR4R chassis

I was just informed that when my engine brake is switched on it will affect the transmission during acceleration. I asked my local garage to check it out and they informed me about it. The transmission would stutter and/or bog down (similar to an old fashioned gas engine vacum issue) when accelerating. Have you experienced this? All the information I have so far only documents deceleration use. I have found no information/documentation re acceleration issues.

Got any information or similar comments?

Michael B

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Old 04-20-2011, 07:33 PM   #2
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I have an ISB 300, Allison 2500 on a Freightliner chassis and I've never noticed any difference in acceleration with the engine brake switch in either position.

David, Judy, Gracie (the dog) and Waldo (the parrot)
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Old 04-20-2011, 07:48 PM   #3
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I have an ISB 325, Allison 2500 on a Roadmaster RR4R chassis. No stutter in acceleration switch on or off. I do notice the shift points change. (Holds lower gear longer)
2008 Monaco Cayman XL 38PBD
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Old 05-20-2011, 08:53 AM   #4
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Just to close this out.
I finally found the problem after many tries and garage time. It was an intermittent fuel supply problem. It was hard to detect as it was intermittent and only showed up when it felt like it. there was no discernable pattern or specific condition that caused it. The inline fuel/water separator was the problem and it is possible the filter had a defect as the problem went away when it was changed the old one only had 5K miles on it. The engine brake switch doe not affect acceleration in any way.

Thanks for all the response's I received
Michael Boyle
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Old 05-20-2011, 11:20 AM   #5
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Thanks to you for reporting the final results. So many times we forget to do this.

Regarding your fuel filter, it is possible you got a bad supply of fuel which clogged the filter, or even an algae growth which could do the same. You might bring along another filter for on-road changing in case the problem returns.

If you would happen to have algae, the use of BioBar is very effective in stopping the little critters. It's popular in the boating and aviation industry for this purpose. I use it in my diesel tanks when I have fuel that is not used within a few months, i.e., between RV trips.
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