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2021 2500 HD downshift clunk


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  • 2 weeks later...
  • 4 weeks later...

Had (older, my latest is 2008) GM trucks for awhile and the transmissions, while reliable, have clunks.  I hope this isn't something worse in your case.  My wife once thought someone bumped her at a light because of the way the trans will randomly clunk after stopping.

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  • 3 weeks later...

My 3 month old 3500hd had a few clunky shifts in the first 1000 miles like that, essentially coasting toward a stop or turn but with a little bit of gas pedal to hold speed a little longer on an incline approaching an intersection it would shift hard from second to first. The transmission software must be adaptive to some extent because It seems to have figured it out and, while that shift is not perfectly smooth, it now does that same shift much more smoothly. I’m at about 1700 miles and it hasn’t occurred for several weeks. My foot has probably adapted some too, giving less pedal in those situations. 
 

Overall I think the transmission operates very well and is well matched to the engine and rear end (I have stock 18” wheels and tires SRW). 

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  • 3 weeks later...

I’ve recently tried to get it to do the hard shift a few times in the same conditions that it previously did it and I can’t get it to do a hard shift. Apparently it learns not to do it eventually. I’m at 1800 miles. 

Edited by Another JR
Clarity
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  • 10 months later...

My 22 started doing this a few days ago at ~4500 miles. Never noticed it before, but it dives pretty hard into first out of second now and an audible clunk is heard as presumably the driveshaft slacks from the hit.

 

I am wondering if it's related to trans learning. It has smooth shifts from 1-6 and from 6-2. Slow speed coming to a stop is when it dumps into first and clunks. It's not overly aggressive yet but as mentioned you can hear it and feel it. My only other thoughts as to why could be a stuck accumulator or some other mechanical valve body malfunction.

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