Clunk heard when letting on/off gas?

[solarflare]

Just curious, I have an 08' H2, and just recently I noticed that I have a clunk when I take the foot off or put it on the gas pedal.....It's a hard noise to describe, but it's almost like the driveshaft making the noise.....It doesn't do it all the time, but it's annoying.....
It's only started doing this since about a week ago. I have approx 6800 miles on her now....any thoughts would be great!

[lasvegash2]

mine does the same thing....

[TGCOFTN]

My 2008 does the same thing.............my 2007 dont make the noise.

I know the noise your talking about, but I dont know how to describe it on a message board, LOL

[solarflare]

yeah, it's really hard to describe what it does...scared me yesterday though...I was in traffic and coming to a stop, and the front end went bang. Seems like a driveline issue. I did find that there are a lot of TSB's in regards to this problem, and that there are updates to correct it. The only problem is I don't know what the actual bulletins say, I just have the #'s. Here are a few:

99-04-20-002E JUN 08: Drivetrain - Driveline Clunk Noise Information
07338A JUN 08: Campaign - ECM Update for OBD Improvements
08080 MAR 08: Campaign - Reprogram the TCM
01-04-18-001F FEB 08: Drivetrain - 4WD/AWD Driveline Operating Characteristics
01-07-30-042E MAY 07 A/T - 2-3 Upshift or 3-2 Downshift Clunk Noise

[Stainless]

I occasional hear the same. My service guy said it was from running low octane gas. Are you guys running Premium?

[HummerJim]

My 2008 does it when it's cold or when I get off the highway and slow down to a stop after a long highway drive. I think it's the 6 speed transmission and I really don't notice it that much anymore.

[HumminNBoatin']

most likley the x-fer case.

[TGCOFTN]

I am like you HummerJim, I think its the 6 speed as well. Comparing it to the old 4 speed with the 6.0 liter is a lot of difference. Due to me having both, it was hard for me to get use too. At first I didn't really like it because of all the shifting, but I will say as time goes on, I am liking the 6 speed more and more. The past 5 days, I have tacked on over 2,000 miles on my 2008 H2 and got 19 miles per gallon with it.

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To Stainless, I run Shell V-Power Premium in both of mine. Engine idles smoother, and dont downshift as much, plus you get better fuel economy.

2007 Hummer H2
2008 Hummer H2

[ROX]

Originally Posted by TGCOFTN

The past 5 days, I have tacked on over 2,000 miles on my 2008 H2 and got 19 miles per gallon with it.

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To Stainless, I run Shell V-Power Premium in both of mine. Engine idles smoother, and dont downshift as much, plus you get better fuel economy.

2007 Hummer H2
2008 Hummer H2

19mpg? Really?

[HummerJim]

WOW! 19 mpg is GREAT! The best I've seen on the meter was coming east on highway 70 with a strong tailwind of about 30 mph at 15.1 mpg running premium in a flat area of Kansas running a steady 65 mph on the cruise control for a stretch of about 140 miles with just me in the Hummer. 13.5 mpg is my average on the highway, 11 mpg in town with my lead foot. My problem is the 6.2 is so much fun I tend to get on it a little heavy in stop and go traffic. I think other drivers are amamzed a Hummer can move out so fast!

[TGCOFTN]

Originally Posted by ROX

19mpg? Really?

The truth is, I am actually kinda disappointed in it. I was really expecting BETTER.

I filled up in Hopkinsville, Kentucky and jumped on Pennyrlle Parkway and I did NOT use my cruise control ( I find the cruise control makes the engine downshift more than by driving with your foot. When going up a hill, I can gently ease off the gas pedal to where it will stay in overdrive and not downshift)

Anyways, I kept it at 55mph and those of you who has a 08 with the new 6 speed tranny will know at 55mph the engine is at a VERY relaxed rpm range.

Anyways.......I went to Evansville, Indiana. Then I returned back to the same gas station in Hokpinsville, Kentucky ( I went back down Pennyrlle Parkway again and kept it at 55mph with the pedal and not the cruise control)

Its good.........but not great, and I tell you the # 1 KEY REASON why it wont get better. Thats because the goverment has mandated all this stupid ethonal in gas (which makes it burn faster) so I dont care what kinda car you have, its gonna get less mpg due to the ethonal. The goverment added that in the fuel to help there own self, stop a think.......the more gallons we use, the more they make because they get taxes on every gallon of gas we purchase.

I can remember when the 2007 Escaldes came out with the 6.2 Liter. Gas did not have 10% ethanol in it, and I used The Escalde as a demo and by driving it like a egg was under the pedal, I got 24 miles per gallon with it.

[HummerJim]

I have to agree that cruise control and the six speed go together like oil and water - not very well. Unless it is totally flat, like western Kansas I won't use the cruise control because the constant shifting on hilly terrain is annoying and it can't be good for the transmission over the long haul. I agree in the 50s would be the best mileage, but I'm much too impatient for that.

[HUMMERICH23]

I agree 100% with everything everyone is saying and my sweet spot is going 60mph on flat i get 19mpg easy but then again how long does the road stay flat. At 70 i drop down to 14mpg. I love putting on the cruise control and counting how many times it cant decide whether to stay in gear or drop down to passing gear, its hilarious how bad it is. I get way better MPG when i dont use cruise control on long trips. And the 6.2 does love when it has to past somebody, it redlines fast to get you past! Still have the clunk though, i guess whenever something breaks the warranty will take care of it.

Richard

[OrangeCrush]

Originally Posted by TGCOFTN

and got 19 miles per gallon with it.

God, I hope you're not complaining about 19 mpg. That's almost twice what I get.

[TGCOFTN]

Originally Posted by OrangeCrush

God, I hope you're not complaining about 19 mpg. That's almost twice what I get.

Oh no........not complaining at all. I was just expecting a little better due to driving it like a egg was under the gas pedal.

I have drove it hard, and gotten as low as 11.8 MPG

It really just dont pay to drive the Hummers fast, unless you enjoy just throwing money down the drain for gas. For me, when I go on trips, I normally keep it at 60mph and listen to the XM Radio, or bring some good CD's and just enjoy the drive.

[solarflare]

good gas mileage.....pretty impressive.....well back to my original post....my noise has now gone into a rough bang into 1st gear when coming to a stop.....doesn't do it all the time, but has been getting progressively worse. When it does do it, it seems as though the torque convertor is sticking, and then banging into first.
Any thoughts???? I don't have a hummer dealer close by, and the chevy dealer around here, says just go out and ride it hard.......not to great of a place....

[dbartromsut]

Yep, my 08 does the same thing! It doesn't really sound like it is coming from the engine, so I don't see how running low octane fuel would make it do that. To me it sounds like its coming from the rear end... But mine does it and I do run 87 octane, so maybe. I'll try premium for a while and see what happens! You guys get way better mileage than me! I am lucky to get 10.5 mpg on the highway, but I would imagine that my tires, wheels and lead foot have to do with that!

[TGCOFTN]

Originally Posted by solarflare

good gas mileage.....pretty impressive.....well back to my original post....my noise has now gone into a rough bang into 1st gear when coming to a stop.....doesn't do it all the time, but has been getting progressively worse. When it does do it, it seems as though the torque convertor is sticking, and then banging into first.
Any thoughts???? I don't have a hummer dealer close by, and the chevy dealer around here, says just go out and ride it hard.......not to great of a place....

My 08 does the same exact thing ( I know I have posted this before ) but I just wanted to add a little extra words this time. For me, I have noticed mine tends to do it while slowing down/coming to a stop on a down hill grade. I live on a Hill, and as I am coming down the hill slowing down to pull in my garage, it tends to make that clunk noise going into 1st gear. I am not sure what it is, not sure if its in the Transfer Case, Transmission, or Rear End.
As long as mine is not doing it all the time, I am not going to worry with it due to other 08 Hummers are doing the same thing.

I agree with you, I dont think thats a great dealer just saying to go and ride it hard. Not very professional if you ask me.

[TGCOFTN]

Originally Posted by dbartromsut

Yep, my 08 does the same thing! It doesn't really sound like it is coming from the engine, so I don't see how running low octane fuel would make it do that. To me it sounds like its coming from the rear end... But mine does it and I do run 87 octane, so maybe. I'll try premium for a while and see what happens! You guys get way better mileage than me! I am lucky to get 10.5 mpg on the highway, but I would imagine that my tires, wheels and lead foot have to do with that!

Wow........10.5 mpg.....I dont recall getting that low in my 08 or my 07 H2.
You should try switching to premium and see if you see a increase in miles per gallon. I have been on a trip in my 2008 and ran it 75--80mph and got 13.8mpg. The only thing I can think of is maybe its your tires where mine are factory and yours are oversized.........and then of course running on regular unleaded. For me, I can go more miles on a tank of premium than I can on a tank of regular. With the regular you may save a buck or two at the pump, but on mine, when hitting a hill, it downshifts and acts as if its starving for power. So the buck or two your saving at the pump, your just blowing it out your tailpipe.

Try running a few tanks of premium in it, and see if it improves.