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2005 CTS-V
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Discussion Starter #1 (Edited)
I've been experiencing the famous chatter and had a few questions.

I'm not the original owner of the car, so when I bought it I noticed the chatter almost accidentally while making a very tight turn at slow speed. It's most pronounced when I make the turn with the car rolling in neutral; if while doing this I press the clutch pedal, then it disappears. If I am making the turn with the gear engaged, then it's a lot less pronounced, but can still be heard/felt.

So going back to not being the original owner... when I got the car, I changed all the fluids, including the diff fluid with the GM one and added one small bottle of the LSD additive. Unfortunately this chatter didn't go away.

So I'm wondering if at this point it could be a sign of the clutch pack broken, or if it could still be needing an additional bottle of the LSD additive. Also, when this chatter does occur, is there more wear and tear taking place?

The other crappy part is that all my seals started to leak on the diff case; the pinion seal is the most concerning. Before I sink the money/time into fixing the seals, I was hoping to figure out the chatter issue as perhaps the diff is not worth the replacement of the seals?

Other than that, I don't have differential backlash, and there is no significant whine... I mean there is a very very very low humming sound that I also had with a previous rwd car (G35), so it sounds normal to me.

Any feedback would be great.
 

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2005 CTS-V
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I would start by adding another bottle of additive. The additive alters the friction coefficient of the fluid, and although most units only require the one bottle the fact of the matter is that the ideal friction coefficient can differ from unit to unit. Assuming it is the clutch plates making the noise no damage is occurring. The noise occurs simply because the mechanical forces making the clutches "slip" as opposed to "grabbing" eventually overpower the "stiction" caused by the fluid. (The original Technical Service Bulletin on this issue actually called for disassembly of the clutches and bathing them in the additive. GM has since discontinued that protocol.)

Regarding the seals, you want to check the differential vent (see attached). A clogged vent can cause seal leaks.
 

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So I'm wondering if at this point it could be a sign of the clutch pack broken, or if it could still be needing an additional bottle of the LSD additive. Also, when this chatter does occur, is there more wear and tear taking place?
No damage is occurring, read below.

Chatter is essentially the build-up and release of energy between the differential clutch packs in a limited slip differential during operation. This phenomenon often occurs when torque is transferred between the clutches or when rotational speeds change. During the stick-slip phase, energy is built up to a point where contact between the clutch plates change between static friction (stick) and dynamic friction (slip), resulting in noticeable vibrations. It is this vibration that causes an audible chatter or ratcheting to be heard within the differential. While certainly an annoying characteristic, there is typically no mechanical damage occurring to the differential. It is most often noticed in parking lots or slow driving while turning where the outside wheel turns faster than the inside wheel.

In an effort to control this chatter, friction modifiers are often used. These additives result in a smoother transition between the two states of friction: static and dynamic. Static friction occurs when the clutches physically lock together, while dynamic friction occurs as the clutches are slipping, ergo Limited Slip Differential.
 

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Discussion Starter #4
Thank you for the reply.

I've been thinking about that vent as well. When I was under the car, I found the vent by feel but couldn't obviously see it. From feeling it, it seemed to be dry as well as the area around it, so maybe it is plugged!?

The thing I don't understand from the bulletin is how exactly do I remove the old one? Do I grab the part that's sticking out with pliers or similar and just wiggle it out using force. It's not actually threaded, right? When I do that, will a part of the vent stay in the differential, and that is the part that I have to attach the hose to if I follow the bulletin? And, do you think the job can be done without lowering the diff as suggested?

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Having recollection from a few days back when I was under the car, when I felt the vent, I tried pulling on it and it didn't move. I saw on a different GM forum someone said that when you pull on it, it should move easily. Gonna get under the car now to check the vent as well as the fluid level if I can get the refill bolt off.
 

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Discussion Starter #5
Update: Still not 100% sure how the vent is supposed to be. The only thing I could do is spin the cap of the vent. It didn't pull up. I tried getting the pliers on it for better leverage but couldn't do to very tight clearance. I'd say it's impossible to change it without lowering the differential.

When I opened the fill cap, there was a very faint and short hiss sound. Can that be a sign of the vent cap not functioning, or that could still occur with a perfect cap?

I topped off the fluid, needed to add about 3-4 oz before it started to drip out of the hole. If I had some LSD additive on hand, I would have added it, but I didn't, and main concern was avoiding damage due to the seals leak.

Lastly, I tried spinning the wheels in different conditions:
1. Both wheels up in the air - turning one will cause the other to turn. Transmission in neutral.
2. One wheel in the air, the other on the ground, transmission in neutral - I could turn the wheel that's up the in the air by hand with not too much effort.
3. One wheel up in the air, the other on the ground, transmission engaged - I could not turn the wheel.

I know #1 is normal, but don't know if #2 and 3 are. My LSD understanding is very limited :canttalk:
 

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The service manual simply does not discuss the differential vent and I've never worked on mine - perhaps someone that has will chime in on how to remove it. The hissing sound when removing the fill cap does not necessarily mean the vent does work - it may be designed to exhale when internal pressures increases as the unit heats up when driven but not inhale when internal pressures decrease as the unit cools down when parked. Your description of how the wheels spin under different circumstances appears to be normal.
 
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