Differential Fix

[PeterG]

GM has issued its third update to the bulletin identifying the procedure and oil to eliminate the creaking positraction clutches in our differential units.

My 2007 started making the loudest and most-frequently occurring noise in any several Vette I have owned over decades. The noise started at around 2,000 miles and continued up to 4,500 miles.

My GM dealer's mechanic removed the factory fluid and replaced it with this new GM fluid. This fluid contains a built-in clutch additive and therefore does not need any additional additive.

My mechanic changed the fluid, drove a few figure-eights, and brought the car around to me.

I have not heard a sound -- not any noise -- from the differential !

I have now driven about 200 miles and there is not a sound when turning in any direction to any degree.

The fluid comes in GM-labeled black quart containers. I do not know the part number, but it is specified in the updated bulletin.

GM came through and made our C6s even more perfect!

 

[Tony1Leo]

I'm not sure what exactly the noise you're referring to sounds like, but I get a noise that sounds like medal scrapping when I make low speed turns, especially if there is a dip involved such as coming out of the driveway. I thought it was the tail pipes scrapping up against the frame, but wasn't sure. Mine also sounds like the noise that old springs (shocks) use to make. Can you give a little more details on what the noise sounds like.
Tony

 

[PeterG]

The infamous differential positraction noise sound is generally not more prominent on inclines or declines and is definitely not the scraping of the front air dam nor tail pipes.

It is caused by the irregular slippage -- or hopping" -- between positraction clutch plates inside the differential. My C6 made this sound relatively often when turning a corner in both directions while driving at a very low speed up to faster turns.

It made the noise regardless of the magnitude of the turn. That is, I could make a partial turn in my driveway -- going forward or backward -- and it would make noise.

Sometimes the noise sounded like it was coming from the front suspension.

This sound from my C6 may be described as metal scraping on the ground. My other Corvettes made a similar sound but much less often and for a shorter time during any given turn.

The important point is that I have not heard any sounds since the factory fluid was replaced with the new GM fluid identified in the bulletin.

 

[Tony1Leo]

Thanks Peter. Took it to the shop today and like you said...the noise is gone...hopefully to stay. I'm surprise other people are not experiencing this problem, unless they already knew of it and got it fixed.
Tony

 

[Tony1Leo]

I'm wondering if this problem has damaged the differential. If it's making that much noise, it seems that it would cause some damage. We probably will not find out for years down the road after the warranty has expired.
Tony

 

[PeterG]

I'm wondering if this problem has damaged the differential. If it's making that much noise, it seems that it would cause some damage. We probably will not find out for years down the road after the warranty has expired.
Tony

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I also was concerned about long-term damage to the clutch plates.

My analysis looks at this problem like a problem with a bearing. A clutch is a form of bearing that uses a material that is designed to wear away slowly over time, whereas an engine or transmission bearing is made of a hardened material that should not wear appreciably over time.

In both cases, noise is an indicator of a potential problem and damage and -- at a minimum -- incorrect operating conditions.

In the case of engine or transmission bearings, once they start making noise, I have never experienced a bearing noise vanish after a fluid change. That sort of damage is permanent and requires bearing replacement.

In the case of the differential clutch plates, the noise vanished totally (or at least decreased enough to not be loud enough to transmit into the driver's area). Because the noise vanished, and because the positraction unit seems to work properly, I conclude that no permanent damage was done to the clutch plates. At worst, there was some extra wear on the clutch plates as they hopped across each other.

I plan to trust that the problem has been resolved and that little damage was done. But I will verify this theory before the 5-year warranty expires.