Puzzling thump

[Skybear]

Ok all my TB mechanics….have a 2024 5.3l TB, 10k miles, no major issues and runs fine. Was sitting in a drive through and put it in park as we were waiting. A few minutes later, heard a thump and the truck lurched just as it would if we had been rear-ended. My foot was not on the brake and the parking brake was not on. I got out and saw nothing suspicious. Got back in and everything worked normal. Haven’t had this happen before or since, what in the world would have caused this?

 

[PistolsFiring]

So just a total theory, no basis for this other than what makes sense in my mind. Maybe electronically it showed you were in park (because you put it in park) but it never fully engaged in transmission? So the thump and movement was the “park” command finally enagaging in transmission?

 

[Skybear]

So just a total theory, no basis for this other than what makes sense in my mind. Maybe electronically it showed you were in park (because you put it in park) but it never fully engaged in transmission? So the thump and movement was the “park” command finally enagaging in transmission?

It did feel like a transmission issue…but if it hadn’t mechanically engaged in park, I would think that it would have crept forward as my foot was not on the brake. Maybe it was partially in. I have no idea and have never had a truck do that, but have never had the 10 speed transmission before either.

 

[mrcolieman]

Sounds like your parking pawl settling... If you don't use the parking brake and shift into park, the lever dog may not engage a notch on the pawl gear. The vehicle needs to roll slightly forward or backward to allow the the dog to lock into a notch on the pawl gear, loading the pawl with the weight of the vehicle causing your noise. Parking pawls are not meant to stop the vehicle from rolling away, although they do. The parking pawl prevents power from getting to the drive wheels if the transmission malfunctions. Use your parking brake for parking to avoid damaging the pawl. Generic image below.

 

[Alster]

Not sure if this relates to Skybears post, but ive had a few certain situations where my parking brake would set itself after i pushed the park button on shifter, mostly i can simply shift to Drive and it dis-engages, only once have i had to actually push the paking brake button to dis-engage parking brake. These situations happened at a drive thru as well. The pawl setting makes so much sense
Each time i didn't really feel an extra thump.

 

[Skybear]

Sounds like your parking pawl settling... If you don't use the parking brake and shift into park, the lever dog may not engage a notch on the pawl gear. The vehicle needs to roll slightly forward or backward to allow the the dog to lock into a notch on the pawl gear, loading the pawl with the weight of the vehicle causing your noise. Parking pawls are not meant to stop the vehicle from rolling away, although they do. The parking pawl prevents power from getting to the drive wheels if the transmission malfunctions. Use your parking brake for parking to avoid damaging the pawl. Generic image below.View attachment 22430

Makes sense…is this a GM thing? I’ve owned 7 Ford trucks in my life and never experienced this….this is my first Chevy.

 

[Stormin08]

The LURCH is suspect to a convertor issue....that could be a concern, but it sound like the park brake as well the paw may have saved any further motion.

The 10 speeds are know for issues with heck ball passages and flow issues....typically, the ball wears allowing fluid to bypass...depending on selection ot passage needed, your may have initiated a forward gear, or even something electrical engaging the convertor clutch...

 

[mrcolieman]

Makes sense…is this a GM thing? I’ve owned 7 Ford trucks in my life and never experienced this….this is my first Chevy.

No, its a standard item on automatics of all makes. I found a short video that explains better than I can, although it's an older 4L60 which is all mechanical. Same principle applies for shift by wire transmissions but on those there is no mechanical connection to the shifter and everything happens inside the trans electronically. Hope that's all it was for you!

https://www.tiktok.com/video/7055086737525280046

 

[Skybear]

No, its a standard item on automatics of all makes. I found a short video that explains better than I can, although it's an older 4L60 which is all mechanical. Same principle applies for shift by wire transmissions but on those there is no mechanical connection to the shifter and everything happens inside the trans electronically. Hope that's all it was for you!

https://www.tiktok.com/video/7055086737525280046

Thanks….never owned an electronic transmission before. Hopefully that’s all it was…with all the different issues posted on here, every bump or thump causes me to immediately think the worst.