8-speed transmission Clunking at Low Speeds

LumberMack · April 27, 2019

I apologize if this has been covered elsewhere. However, test drive 2 2019s last night, both 5.3s with the 8-speed. It was raining moderately last night in PA when I tested it out. It only happened once, but when at a low speed (5-10mph), the truck almost lurched forward/jerked shen1 approaching the light. I owned a '15 LTZ with the 6-speed and I remember this truck did this very sparingly when downshifting as it was searching for the right gear.

I have been eyeing an RST for awhile now, but was really a bit concerned when this occurred. Only happened in the one truck (which I found odd), and it only happened that one time during a 5-10 minute test drive, but definitely wanted to get some feedback from those who own the 8-speed? I am looking at probably building one because I want an RST Crew Cab standard bed with very specific options and 20s. Would hate to have any tranny issues on almost a 60k truck. Any and all feedback is much appreciated. Hoping to hear from econometrics, as I know you wrote a detailed review on your RST. Should I be worried?

UGADawgs · April 27, 2019

The only thing I've noticed with 1300mi is occasionally 1st-2nd shift when cold can lurch a bit if light on the pedal. If give a bit more foot or if it's warmed up, doesn't happen.

bigwig · April 27, 2019

I purchased my Trail Boss mid March. The dealer had six on the lot, all with the same build. I drove one that did the same thing. When coming to a slow stop, the tranny would jump a little. The truck did this about 5 times and had like 5 miles on the odometer when I started the test drive, but the problem seemed to go away by the end of the test drive.

I ended up selecting a different color. The one I bought has not had the issue.

econometrics · April 27, 2019

You can read some other discussion on this here:

Silverado4x4 · April 27, 2019

Mine did it when I first bought it but stopped after a few miles after the tranny learned.

AMPRG · April 28, 2019

Now I have 6800 miles on my LTZ. I believe after you put some miles on the truck, it will get much better. I usually have this issue, may be, couple of times per month. To be honest with you, I don't care much about that. I belive this is part of the truck's nature of this transmission and may be fixed with future computer updates. I had the same issues with my previous 2014 LT (6 speed). I sold that truck with 100000 miles with no problem at all.

Don't forget, this is a TRUCK; not a fancy little 1.8L sedan. Roughness is part of the beast's nature ?

oldmann · April 29, 2019

On 4/27/2019 at 7:53 AM, LumberMack said:

I apologize if this has been covered elsewhere. However, test drive 2 2019s last night, both 5.3s with the 8-speed. It was raining moderately last night in PA when I tested it out. It only happened once, but when at a low speed (5-10mph), the truck almost lurched forward/jerked shen1 approaching the light. I owned a '15 LTZ with the 6-speed and I remember this truck did this very sparingly when downshifting as it was searching for the right gear.

I have been eyeing an RST for awhile now, but was really a bit concerned when this occurred. Only happened in the one truck (which I found odd), and it only happened that one time during a 5-10 minute test drive, but definitely wanted to get some feedback from those who own the 8-speed? I am looking at probably building one because I want an RST Crew Cab standard bed with very specific options and 20s. Would hate to have any tranny issues on almost a 60k truck. Any and all feedback is much appreciated. Hoping to hear from econometrics, as I know you wrote a detailed review on your RST. Should I be worried?

This is a common occurrence since the GMT-900 got the six speed transmission. When they shift into first gear they lurch forward a bit. Sometimes the computer will learn to not do that and sometimes your body will learn to avoid it when braking. My 2013 has 170,000 miles on it and it still does it once in a while.

HondaHawkGT · April 29, 2019

It's also something the Ram's ZF 8HP70 was known for. It's called downshift "bump".

April 29, 2019

https://www.autoblog.com/2019/04/25/gm-transmission-class-action-lawsuit/

econometrics · April 30, 2019

Good luck to the owners taking the action against GM. Not sure what they are seeking here, or how they think there’s grounds for a legal battle, but I’ll watch and see what happens.

caddydaddy25 · April 30, 2019

My 2019 RST was doing the same thing about 85% of the time. 7 MPH was the magic number. Whenever I was coming to a stop, once the truck hit 7mph, it would have a hard downshift. My local dealer did a fast relearn and my truck has not repeated the issue anymore since then. When I took it in, it had 250 miles on it. I'm at about 850 miles now.

LumberMack · April 30, 2019

8 hours ago, caddydaddy25 said:

My 2019 RST was doing the same thing about 85% of the time. 7 MPH was the magic number. Whenever I was coming to a stop, once the truck hit 7mph, it would have a hard downshift. My local dealer did a fast relearn and my truck has not repeated the issue anymore since then. When I took it in, it had 250 miles on it. I'm at about 850 miles now.

At least this seems correctable. Still amazing to me that you should have to do anything like this on a brand new truck.

caddydaddy25 · April 30, 2019

I went back to the dealer this morning and had them do a transflush with the new fluid (19417577). I'm not sure if it's just me, but it seems like my shifting is a whole lot smoother. I didn't have a shudder, but I pretended I did because I really wanted the new fluid.

Edited April 30, 2019 by caddydaddy25
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