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boyle908

Engine Braking -- Effect on Transmission

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09 Neptune 35SBD RR4R chassis, Allison 2500MH, Cummins ISB340 11K miles

My transmission was stuttering and bogging down on acceleration. This was intermittent and did not seem to have a discernible pattern or set of conditions that caused it. I had it checked and was informed that with the engine braking switch turned on, it was causing the tranny to perform as described above. This was under low gear (1st & 2nd) acceleration only.

I have not found anywhere in the transmission/owners manual any documentation that implies or corroborates this happening. The coach is currently in for an REK install and I have not had a chance to verify this yet (no issues with the switch in the "off" position). Has anyone experienced this situation or do you have any information on it? Michael B

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Michael,

There could be different causes depending on your Auxiliary Brake System. Is it an Exhaust Brake or a Jake Brake? One affects the exhaust and the other affects the valves. If it is an exhaust brake it may be sticking. However if it is a Jake Brake it could be in the electrical system. You need a service tech to look at it. I may have my terms wrong but you get my meaning. :unsure:

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Guest BillAdams

Yes, but you don't know if that's correct or not. Let us know after you drive it.

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Yes, but you don't know if that's correct or not. Let us know after you drive it.

Finally got to check it out. It happens regardless of switch position.

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Guest BillAdams

If the switch position does not matter, then their statement that the engine brake being turned on was causing your transmission problems is incorrect -- unless the switch itself is defective and the engine brake never turns off. In general, your engine brake should have no interaction with your transmission performance (especially during acceleration), so I find their comments to be suspect, anyway.

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If the switch position does not matter then their statement that the engine brake being turned on was causing your transmission problems is incorrect unless the switch itself is defective and the engine brake never turns off.

In general, your engine brake should have no interaction with your transmission performance (especially during acceleration) so I find their comments to be suspect anyway.

I agree with you about their comments. I am concerned about finding someone locally (San Jose area)who can actually & intelligently diagnose and repair. I have been researching and have some thought as to what it could be, Change solenoid, the inhibitor/limiter device that stops it from doing damage to itself or possibly engine fuel filter/s although I did not notice any sluggishness on the engine but it seems feasible. The transmission should not move @ all if there is something wrong according to the what I have read the controller should stop it from moving.

Forgot to add that it could be a throttle position sensor issue

Still working on it! Thanks for your help

Michael Boyle

Edited by boyle908

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My final resolution did not post for some reason.

I took the unit to FJM trucking in San Jose and within 2-3hrs they found the issue. The primary fuel filter was the issue. On my 09 Neptune/RoadmasterRR4R/Cummins340/Allison 2500 it was located in the hydraulic leveler pump compartment. On the opposite side of the engine to the secondary fuel filter, I had assumed that is was a filter for the hydraulic system (silly assumption) My only excuse is that it had hydraulic lines all around it and even today it looks like part of the HYD system.

They replaced the filter and all is well.

Michael Boyle

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