2021 2500 HD downshift clunk

SteveSr · May 20, 2021

I have noticed that when coasting up inclines, when the transmission downshifts in the lower gears there is a loud clunk. Truck has 2000 miles. Anyone else experiencing this?

TrailBoss1 · June 1, 2021

I have 5,900 miles and have noticed this several times recently when coasting to a stop. I had a 5.3 with 8 Speed which was known for this (I seldom experienced it) and the downshift with the 6L90 was equally harsh.

ARM3 · June 29, 2021

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.

55deere70 · July 1, 2021

I just bought a 2020 gasser with less than 500 miles on it. Just over 1000 on it now and experience the same downshift clunk at low speed. I'm hoping it goes away.

Another JR · July 18, 2021

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).

Another JR · August 4, 2021

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 August 4, 2021 by Another JR
Clarity

Epsilon Plus · June 18, 2022

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.