The "Clunk": Here's what I'm going to do [new info and links from CTS boards]

[PAO]

Originally Posted by LatinVenom This is the reason I have always said is the way you drive this car, I do not have the noise, that said maybe in some cars the transmission lash is a bit more noisie than others.

Windface...thanks for the skilled input.....to those of us that are somewhat mechanically challenged..so to speak!!!!

[Adrenaline]

Anyone else get a slightly weird noise around 2700rpm-3000rpm? It's kinda weird and goes away after that range.

[LBJay]

http://www.cadillacfaq.com/faq/answers/dlinenoise.html

Why does my driveline make a clunking noise? UPDATE: This product from BMR claims to fix it: Http://www.bmrfabrication.com I have done quite a bit of work on the clunk issue since I have the problem on my CTS-V. The problem comes from the soft rubber torque coupling and the drive shaft center bearing mount. Both of these parts are made with rubber that is very soft to reduce road and gear noise inside the car. The clunk occurs when the clutch is suddenly released when there is torque on the drive shaft. The large amount of torque created on the dirve shaft in low, second, and reverse twists these rubber components like a rubber band. When you push in the clutch quickly this torque is suddenly released and the rubber parts quickly unwind. GM calls this torque reversal, but it is not actually a reversal. The clunk noise actually is not made by the drive shaft. The clunk comes from the ring and pinion gear in the differential box. When the drive shaft unwinds suddenly the pinion teeth impact the ring gear teeth and you hear the noise. The noise is loudest if you stand outside near the rear wheels. The noise is comming through the axles and into the wheels, but it is all caused by the soft rubber in the drive shaft. Some of this sudden unwinding is caused by the drive shaft itself since it appears to made from aluminum. Aluminum has one third the stiffness of steel so this causes some of the problem, but I think 90% of the problem is from the rubber. I have had emails on this subject going through the Southeastern Cadillac service rep to power train engineers at GM. Here is their response: "The CTS-V driveline has a few "normal" operating characteristics that some customers may find objectionable. Obviously this is because the driveline was designed with high speed performance and durability as the primary criteria, pleasability issues that normally rank as high Cadillac priorities were relegated lower because this car is not like other Cadillac's. We know torque reversal in the driveline will cause an audible clunk and this can occur under various common driving/clutching conditions." "Torque reversal is a result of normal axle backlash, the driveshaft rubber isolation flanges, the center support and the dual-mass flywheel working together. This phenomenon has been thoroughly evaluated by engineering and has been validated as not detrimental to durability or high performance usage. It is normal and no repairs should be attempted." They will not give me the e mail address or the phone number of the engineer. Please send an e mail to: mike.bojko@gm.com and complain about this problem. Mike is the service manager for the Southeast and he will forward your comments. You can create the clunk without moving the car. Put the parking brake on. Shift to first gear. With the engine at idle (about 1000 RPM) slowly let the clutch out until the engine bogs down to about 600 RPM. The very suddenly push in the clutch and you will hear about three clunks. Do not give the engine any gas when you are doing this. Just idle speed is good enough. I actually blocked the car up very safely and got under the car. I trained my wife to go through this procedure while I was under the car, and I could see the drive shaft clunking back and forth. In my younger days I was a power train engineer for off highway equipment so I know something about this issue. To me it is an unacceptable defect in the design of the CTS-V. So far Cadillac will not try to correct the problem. If you complain it will help. They tell me I am the only one complaining. The solution is to make these rubber parts from higher durometer (stiffer) rubber. Please give me a call and I can tell you even more about trying to relsove this issue. My daytime phone numbers are 803-822-7400 or 803-429-7000. thanks Robert N. -------------------------------------------------------------------------------- This site is not affiliated with General Motors or Cadillac. All trademarks are property of their respective owners. All pages copyright Http://www.cadillacfaq.com. Donate to keep this site live and ad free Here Main Page--- FAQ Main--- List Style FAQ--- Document Library--- Image Library--- Video Library--- Vendor/Mod List--- V Newsletter--- For questions or comments email ctsvett@verizon.net

Since it is the CTS diff, could be the same problem

[PrintMan59]

My thought is simple - if you can here a "clunk" then the stereo must not be turned up loud enough!!!!!

[Larry Karpiak]

Can I ask you guys a favor.
My Solstice arrived this morning at the dealership and I am picking it up Saturday morning the 31st. But I took one they had in the showroom for a test drive and I heard the clunk, and also heard it by just putting in the clutch.. not even while driving. Can you guys try just clutching (if there is such a word) engine running, in neutral, and without the car being in motion. Does it make the noise? I'm really curious

One other thing...Any one who does respond to this tread if you could say whether you do or do not have the LSD. That would be helpfull to everyone.
I do not have the LSD and will post my findings this weekend whether I clunk or not.
Thanks
Larry

[mceb]

Originally Posted by LBJay http://www.cadillacfaq.com/faq/answers/dlinenoise.html Since it is the CTS diff, could be the same problem

Good find That looks like the deal. The wording is even similar to the GM bulletin on the clunk to Pontiac. Looks like Caddy had it as well.

And here is the text from the aftermarket company that claims to have fixed it for Caddy (http://www.bmrfabrication.com/CTS-Vpage.htm)

The differential is mounted to the rear cradle by soft rubber bushings. There are two bushings in the rear and only one in the front. This front bushing is responsible for maintaining pinion angle which is critical for u-joint life, launch consistency, and overall driveline efficiency. By simply releasing the clutch at idle with the brake on, the stock, unsupported pinion measures up to 2 degrees of deflection. Aggressive driving loads this bushing significantly more allowing up to 4 degrees of pinion deflection before the OE bushing "bottoms out". Our Pinion Support adds a low deflection polyurethane bushing to the front mount and reduces deflection to almost zero off idle. The result is immediately noticeable as it removes the "spongy" feel noticeable off idle and decreases the audible "thunk" heard when the OE bushing bottoms out. Available in red or black powdercoat. Simple 1 hour installation.

[brentil]

Sweet, I wonder if that same bracket can be used on our car, or if the mounting is different for us?

[mceb]

Some cool stuff on that caddyfaq site. They have links to service manual pages including a section on the diff...

http://www.cadillacfaq.com/faq/

[windface]

Post #18 is interesting but... I don't think so. Now guy's I sure don't claim to have the final word on this, in fact after my brief drive this morning I can't touch our Solstice. The boss is on the phone as we speak, trying to bring in a buyer. Needless to say he don't want it in the shop surrounded by tech's trying to figure out a problem. But I heard enough of the clunk noise this morning to say my post #14 stands. I've heard this noise in other manual transmission cars, to a lesser degree, but under the same conditions. That is applying and releasing torque to the driveline. In my opinion it is the sound of gear lash. I do however have a theory of why it is more noticeable in the Solstice. First, the transmission is out of a truck, so the tolerances are probably somewhat wide. (It's also probably strong enough to haul a motorhome out of a ditch.) Secondly, it's all hooked up to a super rigid platform, that in effect gives the driver a more "close" relationship to the driveline. Add these two together, and this noise could be the result.. Again, this is a theory, but for now, it's my best guess of what's happening here. I really don't think there is a durability issue at all. Rest assured if I find out anything new on this issue I'll post it. And thanks to everyone else that has researched this concern, and posted. windface.

[SolsticeMan]

Windface, no dis' intended for the following:

I too, have heard the noise from outside the car, as well as inside the car. I've also had the privilege of hearing it on the rare Caddy CTS Manual transmission. The noise is pretty much identical, but much more muffled in the Caddy.

It SEEMS like it is coming from the trans, but I know it is def the differential. The noise comes from the diff and carries directly into the structure via the forward mount of the differential.

Here's what I've been told... making the diff mount harder may (only MAY) help the clunk, but makes a whining noise much worse, and can be an even more annoying problem. Additives and adjusting the friction have no effect. The problem seems to occur more often on LSD version, but is not a definite - IOW you can get the clunk to sound whether you have the Getrag open or LSD. There are varying degrees of severity.

So, I respectfully disagree that it is coming from the trans - PROVIDED you and I heard the same thing. For all I know, the front driveshaft coupler bolts may have been loose in the car you heard...

Good luck, though, and post your results if you get a chance to check the effectiveness of additives and such.

[Critterman]

Windface - did you use a scope to pinpoint it? If it is as you say (and I have no reason to doubt you), would some sound deadening material in the tunnel help?

[windface]

Originally Posted by SolsticeMan Windface, no dis' intended for the following: I too, have heard the noise from outside the car, as well as inside the car. I've also had the privilege of hearing it on the rare Caddy CTS Manual transmission. The noise is pretty much identical, but much more muffled in the Caddy. It SEEMS like it is coming from the trans, but I know it is def the differential. The noise comes from the diff and carries directly into the structure via the forward mount of the differential. Here's what I've been told... making the diff mount harder may (only MAY) help the clunk, but makes a whining noise much worse, and can be an even more annoying problem. Additives and adjusting the friction have no effect. The problem seems to occur more often on LSD version, but is not a definite - IOW you can get the clunk to sound whether you have the Getrag open or LSD. There are varying degrees of severity. So, I respectfully disagree that it is coming from the trans - PROVIDED you and I heard the same thing. For all I know, the front driveshaft coupler bolts may have been loose in the car you heard... Good luck, though, and post your results if you get a chance to check the effectiveness of additives and such.

SolsticeMan, If the noise turned out to originate from the rear end, I got to tell you I wouldn't pass out from shock. Your exactly right in that sound travels through a structure, and thus can be extremely hard to pinpoint it's origin. I can't tell you how bad I wanted to, as Critterman mentioned, put our sound scope to work. But as I explained it just wasn't possible. I am close to 100% certain the noise is lash in the driveline. I still am going to hold onto my theory in post #24, at least on the car I drove this morning. But again, I have to make clear the fact that it is just that..a theory. Also I did nix the additive idea since I drove the car (see #14), I don't think it would help.

[Critterman]

I was just wondering if you would get enough noise out of it in the air without a load, the only way I know to get a scope on it. Otherwise it would be real tought on the elbows and knees getting dragged along under the car.....

[bradyb]

Could it be duplicated on a dyno?

[windface]

Originally Posted by Critterman I was just wondering if you would get enough noise out of it in the air without a load, the only way I know to get a scope on it. Otherwise it would be real tought on the elbows and knees getting dragged along under the car.....

Critterman, we actually use probes that attatch to "suspect" parts of the car then listen for the noise through old fashion headphones. Thus the car can be field tested.