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2019 Z71 transmission stumble after backing up driveway

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My 2019 Z51 (5.3l) has a bad stumble as I shift into drive following backing up my slightly sloped driveway. My driveway is the only place I notice it but then again I rarely back up a sloped section anywhere else so not sure if it happens all the time or just after starting up a cold engine. Here's when it happens


  1. Start engine to go to work
  2. Back up my 100' slightly sloped driveway in reverse
  3. Pull onto flat street, shift to drive
  4. Give it a little gas and then it stumbles


The heavier I give it gas the harder it stumbles, getting it's act together after a few seconds and no further problems. Currently I anticipate the stumble so wait a second after shifting into drive, then really baby the gas the first few seconds which avoids most of it.


What the heck could be causing this? It's done it from day 1. Dealer says they can't replicate and fluid levels good.

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#20-NA-102: Lack of Acceleration Followed by a Clunk Feeling After Shifting From Reverse to Drive - (May 14, 2020)

Involved Region or Country

North America


Some customers may comment that after traveling in reverse and shifting the transmission to drive, the vehicle may experience a lack of acceleration followed by a clunk or harsh downshift feeling.


This condition may be caused by the fact the vehicle not coming to a complete stop before shifting from reverse to drive.


If the transmission output speed (OSS) of the transmission does not obtain 0 mph/(kph) before shifting from reverse to drive, the transmission will be commanded to start in 2nd gear. Upon increasing the throttle, the transmission will command a 2-1 downshift, which will be harsh.

The OSS may appear to obtain 0 mph/(kph) when reviewing GDS data. However, the filtered signal as determined by the Transmission Control Module (TCM), may be above the 0 mph/(kph) threshold required by the TCM.

The vehicle must come to a complete stop prior to shifting the transmission from reverse to drive.

Important: Replacing components on the transmission will not provide a resolution to the customers concern.

The information found in this bulletin can be shared with customers that may inquire about this condition.


Edited by newdude
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1 hour ago, B.R.67 said:

I have the same problem on my 5.3 8 speed 2019 Z-71. I'm unhappy with the 8 speed transmission overall and will not have one in my next truck.


1 hour ago, EagleRising said:

I have the same problem and got told the same. Everything checks out no issues.

Sent from my SM-G975U using Tapatalk

Look at what Newdude posted, it's the driver not the vehicle.

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Your tech quit looking to soon? 


Seems like it needs 3 seconds for a 'garage shift'.


The is also a test procedure so tech can see if there is a problem that needs to be corrected.





Delayed Transmission Engagement

September 30, 2020

Some 2018-2019 ATS, CTS, CT6, Corvette; 2018-2020 Express; 2018-2021 Camaro, Colorado, Silverado, Canyon, Savana, Sierra; and 2021 CT4 models equipped with the 8L45 or 8L90 8-speed automatic transmission (RPO M5T, M5N, M5U, M5X, MQD, MQE) may have a delayed engagement condition when the transmission is shifted from Park to Reverse or Park to Drive after the vehicle has been sitting with the engine off. (Fig. 12) The delayed engagement typically occurs after several hours or, more commonly, overnight.


F12-trans-shift-3.pngFig. 12


The condition may seem to be delayed gear engagement, a slipping transmission, or delayed engagement followed by a harsh engagement.

The transmission is designed to allow three seconds to complete a garage shift (shifting from Park to Reverse or Park to Drive). If the engine speed is increased before the transmission has engaged, the garage shift may be harsh.

After the initial shift, transmission operation will be normal for the subsequent engagements. The condition will not occur again until the vehicle sits again with the engine off for several hours or overnight.


Delayed Engagement Test

Use GDS2 to monitor engine RPM and the transmission input speed sensor (ISS) prior to starting the engine. Start the engine with the transmission in Park and shift the vehicle from Park to Drive or Park to Reverse with the service brake applied. The ISS should drop to zero within three seconds, which is the clutch engagement time. Recording the GDS session log can be useful in diagnosing the condition.

Delayed engagement of Park to Reverse or Park to Drive is present if the time difference between the gear selected (Pt. 1) and the transmission input shaft speed reaching 0 RPMs (Pt. 2) exceeds three seconds. (Fig 13)


F13-trans-shift-1.pngFig. 13


In most cases, the transmission will engage in three seconds or less, which is considered an acceptable engagement time and no repairs should be attempted.

TIP: The vehicle should only be evaluated after sitting for a minimum of eight hours but less than 24 hours and at an ambient temperature of 50°F (10°C) or above.

If engagement time exceeds three seconds, attempt to learn the C3 – Drive and C5 Reverse – Clutch using the following steps:

  1. Allow the transmission sump temperature to rise between 20° and 30°C (68° and 86°F). Do not apply the accelerator pedal.
  2. Perform 20 Park to Reverse shifts or 20 Park to Drive shifts releasing the brake pedal with each shift, allowing the vehicle to roll 5-10 feet (1.5-3.0 m) per engagement into gear.


If the learn procedure does not correct the condition, disassemble the transmission and inspect the 1-3-5-6-7 Clutch (C3) for a delay into Drive condition and inspect the 4-5-6-7-8 Reverse Clutch (C5) for a delay into Reverse condition. The respective clutch plates and seals should be inspected for wear and or damage and repaired accordingly.

If the vehicle has less than 2,500 miles (4,000 km), the transmission or valve body has been replaced or a clutch repair has been performed, follow the clutch learn procedure in Bulletin #16-NA-019 to learn the C5 Reverse and C3 Drive Clutch.

For additional information on a delayed transmission engagement condition, refer to Bulletin #20-NA-187.


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Quick one-word overview of my experience with this exact same problem:  lemon.


More details:  Within 3 months of buying a 2019 RST (5.3L, 8 speed), I began experiencing the dreaded reverse to drive clunk.  Took it to the dealer and the code(s) showed a problem with the torque converter.  As it was being replaced, the mechanic noticed debris and a loose shaft in the transmission.  Transmission replaced too. 


Problem continued.  Also experienced a similar clunk when slowing down then accelerating.  For example, approaching a red stop light that turns green followed by acceleration.  Another example:  exiting the highway, slowing down on the ramp, and then accelerating into the turn.  Mine mostly manifested itself with a brief hesitation, followed by a clunk and sometimes a skipping/chirping from the rear wheels.  This happened on average once a week (some weeks 2-3, other times none). Problem occurred more during sub 32-degree weather.  A return to the dealer and I got the same response as others:  normal operation, not a problem.


I strongly disagreed. The clunking was substantial, not a mere inconvenience or rough shifting. I was reluctant to tow or haul with the issue. My truck was in the shop for over 30 days.  I filed a lemon law claim. I argued the problem substantially diminished the value, safety, and use of the truck.   In the end, the arbitrator ruled in my favor and GM was ordered to repurchase my truck (original purchase price + sales tax + state fees + dealer fees + interest on loan).   The dealer was very good throughout the process.  No issues whatsoever with them.


Any way to change my forum name to Not_An_RST19Fan?  :)

Edited by RST19Fan
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