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Old 08-18-2019, 11:23 AM   #1
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Allison 3000 Transmission

My transmission has decided it doesn’t want to automatically downshift from 4th to 3rd. If I pull it down manually it’s fine. Upshifting is normal, all other gears are normal. Filters have been changed, fluids changed within the last 18 months, no prior issues. 75k on engine and tranny. Any thoughts?

2008 American Coach. 425 ISL Cummins. Allison 3000

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Old 08-18-2019, 11:49 AM   #2
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Quote:
Originally Posted by Scott98 View Post
My transmission has decided it doesn’t want to automatically downshift from 4th to 3rd. If I pull it down manually it’s fine. Upshifting is normal, all other gears are normal. Filters have been changed, fluids changed within the last 18 months, no prior issues. 75k on engine and tranny. Any thoughts?

2008 American Coach. 425 ISL Cummins. Allison 3000

Thanks
My only suggestion would be for shutting off all power, by disconnecting all the neg. terms. of the batteries for all night and then for trying it, the next day. Other than that, take it to an Allison shop for having it reprogrammed and you may be able even tell them, what you want the tranny to do, since there's usually choices in the way it operates.
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Old 08-18-2019, 12:12 PM   #3
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Does it get past 3rd, i.e. 1st or 2nd when you come to a stop?


When you manually shift to 3rd, does it actually go there (rpms increase)? The Allison considers the shifter position just a target and does not necessarily go to that gear at all. Third is a very transient use gear in most applications, just a brief use as you accelerate from a stop. Mine hardly ever used 3rd downshifting - if it needed to get below 4, it was almost always headed to 2nd.
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Old 08-18-2019, 03:12 PM   #4
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Scott I had issues with my Alison and it turned out to be a couple computer sensors not communicating. I took it to Freightliner and there was a recall on one of the sensors. They fixed it under warranty and all is good now. I never received a notice of the recall.

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Old 08-19-2019, 09:55 AM   #5
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Does it get past 3rd, i.e. 1st or 2nd when you come to a stop?


When you manually shift to 3rd, does it actually go there (rpms increase)? The Allison considers the shifter position just a target and does not necessarily go to that gear at all. Third is a very transient use gear in most applications, just a brief use as you accelerate from a stop. Mine hardly ever used 3rd downshifting - if it needed to get below 4, it was almost always headed to 2nd.


Gary
Yes, the RPM’s increase when I manually shift to third. I’m out west and 43’ long and pulling an F-150 so it quite frequently needs to use 3rd when climbing. All my other shift points kick in around 1600 RPM. When in 4th and headed for 3rd, it acts like it wants to shift down, but doesn’t.
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Old 08-19-2019, 12:57 PM   #6
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Yeah, 1600 rpms is the peak HP output of a typical ISL so where the Allison likes to hang out when under load. It will simply not downshift if it is already achieving optimal engine power.
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Old 08-19-2019, 05:44 PM   #7
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Do you have the tranny in Econ mode? It changes the shifting when in that mode.
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