Got an appointment Tuesday the 12th to get the reprogram done. Will report my findings back to let y'all know if it's worth having done. Not expecting the full Monty on this but fingers crossed for something...

 

Just waiting around till the 12th and bumping this so it doesn't get lost

 

At the stealership as we speak…

 

As William Shakespeare once said, "Well, ****!" No discernible difference in the low-speed clunk after having the ECM reflashed. There did seem to be less downshifting going up inclines, so if that's better then it's worth the $85 plus tax it cost me.

Did a little experimenting though. I selected manual and then went through the first four gears using the flappy paddles to see if maybe the slack is in the tranny. In each gear there's a goodly clunk at speeds below 20 mph when alternately letting off the gas and hitting it. So that should eliminate a clunk due to a tranny shift at the same time as hitting the gas.

So. Guess I'm stuck with this clunky GM driveline. Someone suggested the chain in the transfer case but don't see messing with that anytime soon! Cheers everyone.

 

That's a bummer, I was hoping that would do the trick. Maybe it's TSB that was posted earlier: http://www-odi.nhtsa.dot.gov/acms/cs...43845-3346.pdf

But that one seems for more extreme issues.

 

Yeah, don't have any of those going on.

 

So to make the clunk happen your driving about 20mph then lifting off throttle then hitting throttle right away? Hate to say it but if that's the case, don't do that. As you lift off throttle driveline lash reverses and to stab throttle again right away is forcing all that lash to be taken up in the opposite direction. Any 4 wheel drive will do this to some extent. Each component(axles, ring and pinion, t-case, transmission) has gear lash. If they were tight they would bind up, overheat and destroy themselves. More noticeable I 4 wheel drives due to extra component(transfer case) Not to mention all wheel drive then your adding front diff into equation. A little more gear lash in any one or more components compared to a similar truck will amplify noticeable clunk. Does not mean its worn out or falling apart. Normal driving normally doesn't include lifting and stabbing throttle at low speeds.

 

I have to respectfully disagree. I have driven all wheel drive vehicles for decades and the last one was a '97 fj80 w/ 200k on it (off roaded that thing a lot). None, not a 1, had any noticeable driveline slack.

But I am starting to believe this is a unique thing to GM's and as you describe is normal.

Not trying to start anything. But until I drive a handful of H2's that all have this, I will continue to look for a solution.

 

The only real fact I have is my '04 doesn't do this at all, or if it's there it's below the level where it's noticeable. I put 152k on my '05 F250 4x4 and it wasn't detectable in that one, either.

HUMTECH, the sort of driving I was trying to duplicate is the good ole', somebody pulls out in front of you and you have to hit the brakes, then resume the throttle to continue the interrupted journey. I'm not a throttle-puncher or leadfoot, I'm pretty wimpy ever since the oil embargoes and gas lines of the 70s and 80s! Might just be my '08 but when incidents like the above happen, or I'm not paying attention to a slower driver in front of me, or the light turns green and the guy or gal in front of me doesn't go but I do, etc etc, then this happens. And in city traffic it goes on all day. That's all I was trying to duplicate, should have been clearer.

 

Ok that makes more sense, we had a customer that had same concern that we could not duplicate so I finally had him drive it to show me. He would jump on and off the throttle like he was playing the drums and says "did you feel that" of course I felt it and calmly told him not to do that anymore. He wasn't satisfied with my response. So to me it now sounds like maybe there is excessive driveline play in your truck. Best way to tell would be to drive another one of the same year, same trans and gear ratios.