slow speed suspension clunking

Gthompson · March 21, 2020

I'm having some issues with my brand new AT4. Just purchased a 2020 AT4 (2 weeks ago), had 24 miles on it. Within 100 miles it started making a clunking sound under the bed. Another 50, the steering started pulling and I had to take it in. Took it in and they tightened the u-bolts for the leaf springs which fixed most of the problem. The issue I still have is an annoying clunking sounds somewhere towards the middle of the truck, all the time. Happens at every stop sign, every turn, every speed bump. It's driving me crazy. The last time the dealer wouldn't even take it in. They said, "let us do some research before we bring it in." The suspension definitely doesn't feel like it did day 1, feels a lot "looser" and the clunking sound is tough to deal with.

Anyone having similar problems? Find a fix for it?

Thank you!

davester · March 21, 2020

go to a different dealer? for them to tell you to not bring it in while they research the problem is just crazy.

Kchampagne · March 22, 2020

My clunking under the bed was diagnosed to be a defective leaf spring. Dealer is going to fix it under warranty. Do you have the diesel? Sometimes the def fluid can slosh around and make a thumping noise.

Gthompson · March 22, 2020

Thanks for the responses. I have the 6.2L. As I mentioned, they tightened the leaf springs, but there could be more to it.

As Davester mentioned, I just scheduled a service at a new dealer to have them look at it.

Kchampagne, let me know if that leaf springs fixes your issues.

Edited March 22, 2020 by Gthompson

Chad's Trail Boss · March 22, 2020

My leaf spring squeak. I can spray lube on them at the plastic pads and that last a few days then starts squeaking again. Very frustrating pita. Dealer has looked at them twice and it’s the same answer. That oh we cleaned them and there’s nothing wrong.

They also want to give me shit because I installed Air Lift load lifter 5000 air bags. Smh.

My rear brakes keep intermittently squealing and they said because I had painted my calipers red that may be causing it. Horse Shit. My dealer sucks.

2019 Custom Trail Boss

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Thomcat · March 22, 2020

Might want to grab and shake the shocks to make sure the bolts and bushings are tight.

Kchampagne · March 22, 2020

The tech at the dealer was able to replicate the noise in the leaf spring by rocking the bed side to side at the axle. Squirt a bit of lubricant in the leaf spring, and the noise would temporarily decrease.

Javier Cantu · March 23, 2020

When they re-torqued the bolts of the rear leaf springs at the dealer they were supposed to also install new rubber insets in the leaf springs. My truck was doing the same thing, after the repair the rear noises in the suspension went right away.

Chad's Trail Boss · March 23, 2020

My stealer looked at mine last week and said the inserts were the correct ones.
Said they cleaned between the leafs real good and it fixed the problem.
This weekend the problem returned.
I have Air Lift bags on the rear of my truck and they are giving me hell saying the bags are causing this issue.
I’ve added lots of air, taken all the air out, and had the pressure up to about 12 psi and various ranges in between and it will still squeak.
Every damn time I bring it in it’s not hardly doing it. I’ve found when it rains or there’s just a lot of moisture in the air, the springs tend to not squeak or not squeak that bad. I keep videoing when it’s bad but I guess that’s not good enough for them.
I’m sick of dealing with this shit and ready to just fix the shit myself.
They say I’ve technically voided my warranty because I’ve modified the rear suspension. SMDH
Screw it. I might as well go ahead and lift it more now.
My rear brakes keep squealing intermittently too and I’ve have videos of that as well.

Gthompson · March 23, 2020

Thanks for all of the responses, I took my truck to a second dealer, they confirmed that I’m just hearing play in the rear differential. They let me drive another AT4 around the lot, same issues. It’s just a clunky truck. Not sure how I missed it during my initial test drive. My last two trucks, 2019 Chevy Trailboss and 2013 F150 were quite a bit quieter.

SRBOSST1 · March 25, 2020

On 3/23/2020 at 5:04 PM, Gthompson said:

Thanks for all of the responses, I took my truck to a second dealer, they confirmed that I’m just hearing play in the rear differential. They let me drive another AT4 around the lot, same issues. It’s just a clunky truck. Not sure how I missed it during my initial test drive. My last two trucks, 2019 Chevy Trailboss and 2013 F150 were quite a bit quieter.

Hey I just wanted to say please check out this other tread its seems these two should be put together.

This shouldn't be normal, I don't want a 50k clunky truck. Maybe we are all hearing the same thing but none of us nor the dealerships can figure it out. I can hear play in my rear axel as well by rocking the box side to side but that's not the noise I'm hearing in the cab while driving and if it is I will be very disappointed.

Gthompson · March 25, 2020

Thanks, Shawn Fox. That’s interesting, going to jump into that conversation. I thought the same thing, I definitely don’t want a clunky 50+K truck. That’s insane to me. Also, considering I just traded a 2019 Trail Boss, which I would guess has the same rear diff with no clunking sound, it’s hard to believe. I’m going to post on the other thread as well. I hope this is the issue and it can be fixed, can’t imagine keeping this truck for long with it banging around from even pulling into a gas station.

Also, good point about the play in the rear axle when you push on the side. I checked a brand new Denali, my old Trail Boss (that's sitting on the lot for sale), a used AT4 and a brand new AT4. They all do that, but I know my old truck didn't make this particular noise.

Edited March 25, 2020 by Gthompson

David Lampkins · March 25, 2020

I am having the same issues. I brought it in the dealership and they tightened bolts, however it was to no real avail. Let's get more people to chime in and maybe GMC will actually do something about this in a TSB...

Gthompson · March 25, 2020

Based on jumping into the other thread that Shawn Fox linked above, I'm trying to find a shop that has chassis ears to narrow down where it's coming from. When my leaf spring u-bolts were loose, I could clearly tell it was coming from the rear of the vehicle. It felt as though the spare tire was loose and banging around. After tightening that, the remaining clunk is farther up in the vehicle. Frustrating.

David Lampkins · March 25, 2020

That is my exact experience as well. Sounds like a loose spare tire. Not a metal clunk but almost like a tire hitting the chassis. Please let me know what you find.