Update on my rear end noises, 2005 C-6

I posted about noises from the rear end of my C-6 coupe. I finally took it to the dealer and took the tech for a ride around and around in the parking
lot. He could hear the noise but wasn't convinced it was from the rear. When we got back inside the service manager had pulled up a bulletin from GM that described the problem exactly.
Condition/Concern: Rear axle chatter or shudder on turns on Chevrolet Corvette and Cadillac XLR
They drained and flushed the rear axle and filled it with synthetic axle lubricant GM P/N 12378261 and friction modifier additive P/N 01052358.
This was 2 days ago and the problem is now completely gone. The bulletin stated that if this didn't fix it then they should replace the right and left rear axle clutch packs. I just hope I don't have any more problems with this. The car only has 4500 miles and is just 18 months old.
They gave me a copy of the bulletin and I have posted it as a jpeg file on my pictures page at Yahoo. If you are interested you can read it by clicking on the link below. It is 2 pages long.
http://photos.yahoo.com/ snipped-for-privacy@sbcglobal.net It covers Corvettes 1999-2007 including Z06 and the Cadillac XLR 2004-2007.
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Ron Stewart
Santa Rosa, Calif.
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Glad you got your problem taken care of, and, thanks for the heads up on the bulletin. My '06 hasnt had any rearend chatter but then again, i did drain the fluid at 3000 miles and put in Royal Purple Synthetic with friction modifier additive.
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Thanks, good info. I have an '04 Z06 and it jerks (very slightly) in a tight turn in the parking lot. I just figured, posi rear end, that's just the way it goes. I have a Jeep with a Detroit Locker, and it's violent, so not bothered by a little shudder. But I will take the tech bulletin and the Vette to the dealer and get the upgraded fluid put in. My Vette has 19,.000 miles on it.
Ed
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My C6 is probably starting to be assembled as I write this (Delivery estimate of Nov.6). Does anyone know if this issue has been addressed at the assembly line, or will Chevrolet change the rear axle lubricants to the (costlier) synthetic and friction modifier only if the customer complains post-delivery?
--
Frank M.

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Doubt there is anything different for the current build but they have changed to the new transmission fluid prior to the '06 production. Most of the rear ends will chatter, clunk, or whatever you chose to call it after they are driven for some time. You have to be looking for that noise or happen to hear it by doing some particular movement of the car. Mine does it and I have no intention of having it changed, it is only a feel good effort in most cases. The lubricant and modifier listed above is what is now in the vehicles and is also stated to use those numbers in your owners manual, page 6-12 in the '05 manual which was printed in 2004.
When I back out of my garage I'm turning the car 90 degrees to start down my driveway. As I stop to start forward I sometimes push the clutch in and let it roll back while changing from reverse to first before it quits rolling. In that brief moment the differential will clunk, it's called slack that is being taken up created by different wheel speeds. If you drive the car in a figure 8 you force slack take-up every time you change direction. The resulting clunk is always there, the intensity of the noise is what determines if there is a problem. I doubt there are many out there that has that ability unless it is loud enough to rock your socks.
In other words it is not an issue that needs to be address, just another news group "the sky is falling" thread.
I might add that I've learned some things about the C6 by looking up these things in the owners manual and the service manual. As an un-required comment I had my C6 serviced last month and when I went to get in it I ask the technician if the zerks took much grease. He explained that they didn't have any, so I show them to him, much to his surprise. Trust you car to be done right at the dealer, yeah, right.
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Dad
05 C6 Silver/Red 6spd Z51
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Dad, My 2005 C-6 was making these chatter/shutter noises everytime I pulled into or out of a parking place. They were getting louder and more frequent as time went on. I drive mine almost every day for shopping. Now that they have changed the rear end lube it is absolutely quiet so I feel that in my case it was certainly worthwhile, especially since it was under warranty. The factory directive says that if the noise continues after changing the lube then they will change the left and right clutch packs. GM must think this is a real problem to undergo all this warranty expense. I just hope it doesn't have to be done every 4500 miles!
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Ron Stewart
Santa Rosa, Calif.
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I know what the TSB says and I'll stick with what I said, most will not require changing. The noise you hear may not be getting louder as much as it may be getting more annoying. My '98 had fuel pump noise when I traded it in with the runflat tires back on it. The guy that bought it came to me to buy the tires I was running before I traded, non-runflats. When he went on his first trip the fuel pump noise concerned him so much he wanted to turn around and go home. I told him it was always there he could now hear it better because of the different tires and forget about it. That was almost 3 years ago and it is still running fine.
Nothing I say is intended to change your mind and you need to feel good about your car so the fluid change did that. I've had mine over 2 years, drive it much more than I should and I won't change that. This weekend I went shopping for a tee shirt in North Carolina, http://www.tailofthedragon.com/ 1122 miles, including 4 passes through the Dragon, in 27 hours. You could smell the oil, brakes, tires, and clutch while running the Dragon but I can't hear the clunk anymore when I back out of the garage. Rolled over 24,000 miles as I came into Ohio about midnight averaging 27.6 MPG and 68 MPH, including the runs through the Dragon. My point is that you're not driving your car with enough spirit to get the rear end to work as it should, the new fluid did the driving for you. My best guess is that the manner in which you drive your car will have it back in to correct the noise again. Ask your dealer's head mechanic if it is possible that the clutches may have been glazed over from easy driving. GM has to warranty cars as well as relationships with the user, I don't have to but I do like to share what I know if it will help a fellow Corvette owner.
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Dad
05 C6 Silver/Red 6spd Z51
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My point is that you're not driving your car with enough spirit to

One of the mechanics who works on my E320 said that a ' good Italian tune up' is good for most cars from time to time....cleans out the injectors and deglazes the brakes, and in this case the posi clutches also.
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Frank M.

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wrote:

I had to step back away from the last post and see if I could say it in a different manner.
By changing the fluid it didn't change any parts and therefore none of the fits, metal finishes, clearances, back lash, or lack there of were changed. The only thing left to be effected is the clutch surface that would have clean lubrication and/or a clean fluid to purge the face of the clutch of some of its possible glazed surface. If that surface glazed in 4,500 miles it will do it in less than that the next time because it already has a head start on glazing that surface if driven in the same manner. The new fluid most likely didn't clean it all off. I'm unaware of what type of flushing method that could be used that might change that outcome.
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Dad
05 C6 Silver/Red 6spd Z51
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Frank, The fluids they put in my C-6 are exactly the same as the ones that were supposed to be there when the car was built. Why they might have to be changed so soon(4500 miles) is a mystery. Maybe because most of my driving has been short trips for shopping.
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Ron Stewart
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