Drive train clunk?
Race Director
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I had this issue with a 08 MZ6 and it was the rear end clutches. I changed the rear end oil with Severe Gear Amsoil and a tube of friction modifier and did a few figure 8's and no more clunk.
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Yes I did, When you loaded the car it sounded like a u joint or a half shaft, or even the loose axle nuts, but I checked all of that. I even checked the sway bar end links. It was the clutches in the rear end not being lubricated. The synthetic Amsoil will fix it.
There has been many threads on this here. I think chevy recommended a different oil.
There has been many threads on this here. I think chevy recommended a different oil.
Race Director
Joined: Apr 2007
Posts: 16,025
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From: Toronto, Canada
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Yes I did, When you loaded the car it sounded like a u joint or a half shaft, or even the loose axle nuts, but I checked all of that. I even checked the sway bar end links. It was the clutches in the rear end not being lubricated. The synthetic Amsoil will fix it.
There has been many threads on this here. I think chevy recommended a different oil.
There has been many threads on this here. I think chevy recommended a different oil.
Le Mans Master
Joined: Oct 2012
Posts: 5,788
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From: Tampa Florida
ALL vehicles have drivetrain lash; some more than others. But it's a necessary evil for gears to engage and disengage properly. The lash is most evident with the driven wheels on the air, be it a car or motorcycle. You can move the wheels back and forth like an inch, and hear the 'clunk clunk' as you do that. Perfectly normal. It's a lot more evident (clunkier) on manual cars, but only noticeable at slow speeds. So don't worry, and enjoy your car .
.
Sir, you stole my thunder. I agree the clunk in an MN6 or my MZ6 is just a part of life and ownership of said car. I can fancy shift and massage the R's to not hear it so much...but when I leave a stoplight with the intent to surely make it past the next one the clunk is just a gonna happen and oh well...
Le Mans Master
Joined: Oct 2012
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From: Tampa Florida
One more thought...older c6's (even my late year 2008 1/2) do not have the upgraded rear diff fluid introduced in 2009 that...since I have switched out...has alleviated the tight turn L/R parking lot turn pops in my vette. There is a friction modifier added that GM has cause for a new product code for 2009+ that will solve that problem. Clutch pack engagement will also be chalky or clunky on occasional still but that is for the manuals MZ6>MN6 types.
Thread Starter
Pro
Joined: Mar 2012
Posts: 639
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From: South Eastern MI Michigan
Well...
I raised the rear end, removed the back wheels and BOTH axle nuts were loose. I didn't pay attention to exactly how loose they were but it seemed that they were both at about 20 foot pounds. I snugged them up to about 120 ft lb. There is a major improvement in the drive train slop.
I am going to need to redo the whole process with some lock tight. Now, I need to decide on red or blue, and do I replace the nuts...
I raised the rear end, removed the back wheels and BOTH axle nuts were loose. I didn't pay attention to exactly how loose they were but it seemed that they were both at about 20 foot pounds. I snugged them up to about 120 ft lb. There is a major improvement in the drive train slop.
I am going to need to redo the whole process with some lock tight. Now, I need to decide on red or blue, and do I replace the nuts...
Team Owner
Joined: Sep 2000
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From: Far NW 'burbs of Chicago
St. Jude Donor '13
If you can get a copy of the latest GM bulletin, it gives a specific grade of red Loctite that can only be removed by nuclear weapons, and the part number for the new nuts.
Dealer did my bulletin once, not sure how they cleaned the parts and which red Loctite they used, but the nuts came loose again after about 40k miles. I was not impressed.
Dealer did my bulletin once, not sure how they cleaned the parts and which red Loctite they used, but the nuts came loose again after about 40k miles. I was not impressed.
Burning Brakes
Joined: Oct 2010
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From: US-ARMY 1974-1996 Retired ; Oklahoma, City ; Atlanta, Ga: Hephzibah, Ga
I am having the same problem as some of the others when car is stopped and placed in drive, then you shift to reverse and it clucks or in reverse and you shift to drive and it clunks? I checked the axle nut yesterday and both were loose so I tighten them up but I noticed the clunk is still there. I am going to get two new axle nuts today from the GM dealer and torque them down this week when the rain stops. You mention the end links were bad on your car. Where are these items located and is it something I can replace. I consider by self a shade tree mechanic. Any pictures of the end links. 
I have an 05/auto. Thanks for any feed back. I didn't have the car jacked up when I tighten them down so I don't know if that would make a different.
I have an 05/auto. Thanks for any feed back. I didn't have the car jacked up when I tighten them down so I don't know if that would make a different.
Instructor
Joined: Jan 2013
Posts: 195
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From: Mississauga ON
I had this sound also, and was only noticeable (because of road noise at higher speeds I suspect) and was very obvious in my parking garage. I have an '08 A6 auto.
Not sure what the root cause was, but it was completely gone after my trans and diff fluids were changed. I will check my nuts next time
Not sure what the root cause was, but it was completely gone after my trans and diff fluids were changed. I will check my nuts next time