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Old 08-02-2022, 01:11 PM   #1
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Hard downshifts sometimes

2021 Class A Newmar on a FTL chassis.

Sometimes, in no apparent pattern, I get a hard downshift. Usually it is 4->3 but sometimes 3->2. It seems to happen more often when I am stopping more quickly than normal. Yesterday it happened a few times in 20 minutes-but that was the first time it happened in months. We are full time.

I was mentioning this to a FTL service guy when I was in for service. He called his “Allison guy” who said this is normal for these newer transmissions with the adaptive programming. Unless something else is happening there is nothing to worry about.

Thoughts?
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Old 08-02-2022, 01:42 PM   #2
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I've had that happen a couple of times and like you it was when I had to stop quickly like for a light changing. In 44,000 miles it's only happened twice.
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Old 08-02-2022, 09:33 PM   #3
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Same issue here.
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Old 08-05-2022, 01:17 AM   #4
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I've experiencedd that too, perhaps 2-3X a yr. I finally reached the conclusion it is a timing problem. Just when the tranny is about to shift I either add or remove throttle, which caused the TCM to abort it's normal pattern.



Come to think of it, that hasn't happened since I replaced the filters and Dextron III fluid 2 years ago, then again, I may be unconsciously avoiding my throttle thing.
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Old 08-05-2022, 02:41 AM   #5
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Adaptive shifting is learned while driving and placed in memory.

If your removing battery power in storage,, it needs to re-learn during the first few miles of driving.

Could it be that ?
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Old 08-05-2022, 11:58 AM   #6
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Quote:
Originally Posted by twinboat View Post
Adaptive shifting is learned while driving and placed in memory.

If your removing battery power in storage,, it needs to re-learn during the first few miles of driving.

Could it be that ?
No. We are full time. We had our house batteries replaced months ago but I doubt that is connected.

Never disconnected the chassis batteries. Are you sure the Allison requires battery power to keep the memory?
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Old 08-05-2022, 12:08 PM   #7
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My vintage Allison 3000 series WTEC III controls , will do this , particularly evident when the exhaust brake is active .
Hard braking when exhaust brake is on, rapid drop in engine RPM and vehicle speed can even result in a double gear down shift .
Doesn't happen often , but when it does your seat belt better be tight.
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Old 08-05-2022, 12:19 PM   #8
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Yup, double downshifts (dropping two gears) often leads to that occasional harsh downshift. Particularly true with 2nd gear pre-select for engine brake.



In an emergency stop-- little you can do about it.


If planned, you can down arrow, a gear at a time then turn on the engine brake. That breaks that one big decel into three "less dramatic" steps: down one gear, down another gear, then engine brake. Keeps from throwing momma into the windshield.
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