Rear end clunk on AT4 HD

[newdude]

20 hours ago, Pryme said:

I’ve read some people having less than right U bolts. I wonder what the spec is for the torque settings on those nuts?

 

@newdude I bet has access to those torque specs?

 

newdude have you seen any trucks with random clunks as the truck goes around turns at low speeds and say over off camber turns into driveways etc?

 

14 hours ago, Jettech1 said:

I can't remember where the post is, this is where you shine bigtime because you save all of this stuff.  Anyhow one person was having clunking issues and took a pic of the U bolts on the springs.  I swear I could see light between the U bolt and the springs.  I'm wondering if maybe these U bolts aren't tightened to specs at the factory, or with the suspension settling in just a hundred miles or so they are loosening up.  All of this clunking noise has to have something to do with the either the springs attachment point or the U bolts.  I can't think of any other way this noise could be replicated.  What are your thoughts Pryme?

 

 

First Pass: 74 lb ft

Second Pass: Loosen 270 degrees

Third Pass: 74 lb ft

Final Pass: 175 - 185 degrees

Edited January 14, 2023 by newdude

[Jettech1]

13 hours ago, newdude said:

 

 

 

First Pass: 74 lb ft

Second Pass: Loosen 270 degrees

Third Pass: 74 lb ft

Final Pass: 175 - 185 degrees

Is this from the factory or is this what the people do at the dealerships?

[Pryme]

8 hours ago, Jettech1 said:

Is this from the factory or is this what the people do at the dealerships?

I’m sure it’s from the factory manual. 
 

so it seems there is not an actual torque spec. Interesting that it requires the torque than lossening and retightening. 
 

maybe she just needs a good run out in rough terrain. Bring the ole girl out to a frozen corn field and send it. 
 

tyat should sort it all out haha. 

[Pryme]

21 hours ago, newdude said:

 

 

 

First Pass: 74 lb ft

Second Pass: Loosen 270 degrees

Third Pass: 74 lb ft

Final Pass: 175 - 185 degrees

Have you seen any reports of slow speed clunks or sounds under these trucks? And if so, what was it?

 

thanks!

[gemarsh]

11 hours ago, Pryme said:

...

maybe she just needs a good run out in rough terrain. Bring the ole girl out to a frozen corn field and send it. 
 

tyat should sort it all out haha. 

A frozen bean field, chasing a yote, will break her in too. Not enough snow for the snow mobile, but just right for the 2500 AT4. 

[newdude]

On 1/15/2023 at 1:29 AM, Jettech1 said:

Is this from the factory or is this what the people do at the dealerships?

 

That is the torque sequence from the service manual. 

 

On the assembly line things may be done differently and they achieve that final torque value with an automated torque device, or they may do it to a different spec and that's why the bulletin exists.  I can't be certain on that though.  

 

23 hours ago, Pryme said:

I’m sure it’s from the factory manual. 
 

so it seems there is not an actual torque spec. Interesting that it requires the torque than lossening and retightening. 
 

maybe she just needs a good run out in rough terrain. Bring the ole girl out to a frozen corn field and send it. 
 

tyat should sort it all out haha. 

 

That is the torque sequence from the service manual.  

 

23 hours ago, Pryme said:

Have you seen any reports of slow speed clunks or sounds under these trucks? And if so, what was it?

 

thanks!

 

We have had one HD for a clunk so far sadly.  Don't recall what we did with it.  

Edited January 16, 2023 by newdude

[ttowntwostep]

On 1/13/2023 at 7:52 AM, Gasman03 said:

I also recently purchased a 2023 2500HD AT4. I started hearing the noise in the rear of the truck before I put 100 miles on it. It is only noticeable with slow speed suspension rock or slightly cambered turns that produces undercarriage clunks. My truck is currently in the shop for the second time, with less than 500 miles on it. To state this is frustrating, is an understatement!

 

OK, so the clunking noise has disappeared with use.  Currently around 950 miles on unit.  Seemed to improve and go away at around 600 miles.  Definitely not something you want to hear out of a brand new truck.  YMMV

 

Now... if I could figure out how to keep the stupid lights from flashing every time the tailgate is opened.  Don't think the whole neighborhood should alerted to the fact that something was put into or taken out of the bed.  

[Gasman03]

On 1/13/2023 at 9:04 AM, Pryme said:

In the shop twice for this clunk sound? Please keep us posted on what you find out. 

My local GMC Dealership went over the entire reared tightening everything to factory torque specs. For now it seems to have stopped making the sound. I will update if it returns.

[Pryme]

1 hour ago, Gasman03 said:

My local GMC Dealership went over the entire reared tightening everything to factory torque specs. For now it seems to have stopped making the sound. I will update if it returns.

That’s encouraging news. Thanks

[Mass2500HD]

On 1/21/2023 at 3:27 PM, ttowntwostep said:

OK, so the clunking noise has disappeared with use.  Currently around 950 miles on unit.  Seemed to improve and go away at around 600 miles.  Definitely not something you want to hear out of a brand new truck.  YMMV

 

Now... if I could figure out how to keep the stupid lights from flashing every time the tailgate is opened.  Don't think the whole neighborhood should alerted to the fact that something was put into or taken out of the bed.  

Follow up. I have to concur. My clunk seemed to dissipate somewhere after 600 miles. I’m currently 1050 and it seems to be gone now. Not sure why, but similar experience  to twostep