Hard down shift while coming to a complete stop - Page 2 - Chevy and GMC Duramax Diesel Forum
11-16 LML Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #11 of 34 (permalink) Old 11-09-2016, 09:20 PM
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I have had the bowling ball rolling to the front of the bed sound on occasion. I think it's just the transmission learning

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post #12 of 34 (permalink) Old 11-10-2016, 07:27 AM
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This has also happened to mine a few times following.. Feels like I ran something over or hit something first time it happened I had to back up thinking I ran over or hit a sign..


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post #13 of 34 (permalink) Old 11-10-2016, 07:34 AM
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Back in 2004 I had this happening on a couple of my trucks. My local GM mechanic removed the driveshaft and lubricated the splines on the output shaft of the transmission. That stopped it.

Not sure if yours is the same issue but might be worth a try.


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post #14 of 34 (permalink) Old 11-10-2016, 08:24 AM
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Most likely the additional 300 RPM, when in regeneration mode, is causing the hard downshift.

For a test-- in a safe area, try holding the RPM 300 RPM higher and come to a stop using your left foot.

My LLY does this on the first few stops, when trans is cold.

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post #15 of 34 (permalink) Old 11-12-2016, 11:20 AM
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Had my 2015.5 for almost a year now. Experienced the same thing from day one. I pay pretty close attention to things going on with my truck and I've finally concluded that the issue seems to only occur during a regen with the idle running about 300 rpm higher. Looks like others are experiencing the same issue.


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post #16 of 34 (permalink) Old 11-13-2016, 07:19 AM
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Originally Posted by bzeller View Post
Had my 2015.5 for almost a year now. Experienced the same thing from day one. I pay pretty close attention to things going on with my truck and I've finally concluded that the issue seems to only occur during a regen with the idle running about 300 rpm higher. Looks like others are experiencing the same issue.


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Same here - only when in regen - it's a thud into first and you really can't avoid it, just need to be ready for it.

I'm honestly used to it, you can tell when the thing is in regen, soft power and it's lazy feeling, not to mention that extra 300 or so rpm at idle.

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post #17 of 34 (permalink) Old 11-13-2016, 09:18 PM
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My 2015.5 would do it on the first three downshifts after the start of a regen, it's like the the ECM forgot to tell the TCM that is has raised the engine idle. After the first three downshifts, it would figure it out. Scared the SH out of me the first time it did it. I don't have those issues anymore now
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post #18 of 34 (permalink) Old 11-13-2016, 09:50 PM
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My 2015.5 would do it on the first three downshifts after the start of a regen, it's like the the ECM forgot to tell the TCM that is has raised the engine idle. After the first three downshifts, it would figure it out. Scared the SH out of me the first time it did it. I don't have those issues anymore now


Are you saying the issue went away completely or that you're just not scared SH'less anymore when it does happen?


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post #19 of 34 (permalink) Old 11-14-2016, 09:29 AM
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Are you saying the issue went away completely or that you're just not scared SH'less anymore when it does happen?


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I am saying that since my truck no longer regens, it is not an issue for me :-)
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post #20 of 34 (permalink) Old 11-14-2016, 09:38 AM
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I am saying that since my truck no longer regens, it is not an issue for me :-)


Well aren't you just special. I'm envious!!!


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