Clunk on acceleration from a stop

[dkad260]

2012 XL Denali AWD, I've read some threads on the motor mounts and the front diff bushing, but this feels like it's in the rear suspension.

I'm assuming it could be the control arm bushings, is this a common item to wear?

I will look at the motor mounts to be sure.

This feels like something moves then stops, ...almost a hard thud, more than what a driveshaft yoke would feel like.

110K miles.

 

[OR VietVet]

Mileage? Can you make it make the noise/feel whenever you want? May well be just gear lash noise. Age of rear diff fluid?

 

[dkad260]

Mileage posted, 110K.

I can make the clunk if I accelerate slightly harder than a soft gradual take off. Gear oil has about 10K.

Gear lash and yoke lash has a different clunk, this is deeper and it's more of a thuuump, if I had to guess the location, it would be the LR area.

At first I thought the spare tire was loose.

Once I take off, if I let off the gas then get back on it, it's quiet.

 

[swathdiver]

2012 XL Denali AWD, I've read some threads on the motor mounts and the front diff bushing, but this feels like it's in the rear suspension.

I'm assuming it could be the control arm bushings, is this a common item to wear?

I will look at the motor mounts to be sure.

This feels like something moves then stops, ...almost a hard thud, more than what a driveshaft yoke would feel like.

110K miles.

Stick with the simple stuff first. Pop the hood and have someone rev the motor up in gear (while holding the brake) and someone to see if the motor rises up or not. If it does, motor mount time.

My symptoms were exactly the same.

Now, if the mount is good, then take a look at the u-joints and rear differential and bushings, etc.

 

[Joseph Garcia]

Another cause could be the slip yoke.

 

[dkad260]

Stick with the simple stuff first. Pop the hood and have someone rev the motor up in gear (while holding the brake) and someone to see if the motor rises up or not. If it does, motor mount time.

So I just did the check, oh yeah....lol, it's definitely the driver's side mount. So much that it's concerning.

I will surely replace both, but need to address the LH side.

Looks like a peach with AWD.

 

[Doubeleive]

So I just did the check, oh yeah....lol, it's definitely the driver's side mount. So much that it's concerning.

I will surely replace both, but need to address the LH side.

Looks like a peach with AWD.

ya these trucks have a tendency to "throw sound" it's happened to me a few times.
I would go with the hummer h2 mount
and I would look into going ahead and doing the diff mounts as well because they will clunk to if not now then later mine was destroyed falling apart.

 

[OR VietVet]

If access requires exhaust manifold removal I would have the clamps at the ready like I did on my 5.3.

 

[swathdiver]

So I just did the check, oh yeah....lol, it's definitely the driver's side mount. So much that it's concerning.

I will surely replace both, but need to address the LH side.

Looks like a peach with AWD.

Something for you to consider, do you want to replace with the original fluid filled mounts or with the Hummer H3 solid mount? The latter is a little smaller and more durable. The number is 25847739 and they are about $90 on Amazon right now. The original mounts are 15854941. "They" say there is more vibration imparted into the cab with the solid mounts. The guys who've done it on here say it's barely perceptible.

It helps to get a little more room by removing the exhaust manifold heat shields and get at the driver's side mount from the wheel well and from the top. The passenger side, you want to disconnect the battery and drop the starter, from the wheel well and below.

Have leaky engine oil cooler lines? Now is the time to change them with that motor mount out of the way!