2008 H2 Clunks When Accelerating
 

Hello all,

I just got a 2008 H2 with 25k miles.
Immediately I notice a clunk / pop when accelerating in between 15-35mph.
It doesn't happen all the time, but often happens when in sit and go traffic and down hill. In other word, when I step on the gas after the truck down shifts, it pops. I can feel the pop beneath my foot, through the floor panel. What's troubling is it doesn't clunk / pop from a complete stop or in higher speed 35 (40) mph and above.

So far the dealer have reset the learning modules on both the car and transmission. Inspected the transmission, but found no issues. They told me it's a 4x4 thing, but I have owned my H2, my other ones doesn't have the same issues.

Please help.

Is it more noticeable if you slow down, like if someone pulls out in front of you, then you hit the gas and it clunks?

Correct.
Another scenario would be if i slow down, and step on the brake when i see a red light in front of me, before I come to a complete stop the light turns green. I would get a clunk every time when i step on the gas.

Or, my foot is on the brake when I going down hill, i would get a clunck as soon as I step on the gas below 35mph, doesnt happen if i am over 35 or 40mph. The faster the mph, the less noticeable of the clunk.

Maybe the slip yoke sticking some or a universal joint on its way out?

I sent it to a hummer (Cadillac) dealer, they checked both Slip Yoke Sticking and Universal Joint, said both are fine.

One of the shop said, it might be the planetary gears, I sent the truck to AMCO.
They didn't find anything wrong with the transmission, just reset some modules.

This comes up on the forum from time to time, apparently it's a known driveline issue with these trucks. All 3 I've had do it. Aggravating as hell. Just put a rebuilt tranny in the wife's 08 two weeks ago and it's not as pronounced but still there. I beat my brains out over that clunk, figured there must be a fix out there. Here's a thread I started on this issue: https://www.hummerforums.com/forum/h...reeplay-37083/

Thanks for the advise. So you think it's the transmission or the drive shaft issue? I have driven 05 - 07 H2, none of them have this issue. I went out to test drove another 08, that one doesn't have the clunk issue.

I'd really want to know the history of the one that doesn't clunk - new/ overhauled/ upgraded tranny or transfer case, different tail shaft, gearing, tuning, whatever could get rid of that damn clunk. If it's not a big diff in price I might be inclined to jump on that one.

Since I mentioned gearing, it makes me wonder if others who have regeared have this issue. Be curious to know if the gearing on the two you drove is stock.

The other one I drove were stock too. It has almost 6k miles