Derek5.7

I've gone on a quest to get answers/leads to this question several times (researching old threads on this list and others) but I always seem to come up short. I have a 2005 CTS-V with Creative Steel engine mounts, tranny mount and rear diff bushing. I have Voodochikn's poly carrier bearing on my driveshaft. I have a version 3 rear differential. I have done the LS7 clutch swap and despite ALL these "fixes" I still get a jarring shudder/shake on engine shut down? Is this simply the price you pay for stiff motor and tranny mounts (I have CS black all around)? Is it unrealistic to think my engine should be a little quieter (i.e. not shake quite so much) on shutdown or at least not sound like it will eventually rattle something loose? I realize LOTS of people report engine shudder on shutdown with worn factory mounts but I have new poly ones. Would going with a softer poly tranny mount possibly soften the engine/drivetrain down a bit. Could I drill a few holes in the solid tranny mount to "soften" it a bit? I don't really want to pull the motor mounts out for softer ones (or even stock) because I love how much power gets sent right back to the wheels. Any ideas?

1yakini

Mine was the flywheel, I assume you changed it with the clutch so no telling. Shuts down smooth now for me.

Derek5.7

I replaced the duel-mass flywheel with the single LS7 flywheel - I was hoping that would eliminiate the engine shudder entirely but it didn't. The engine still does not shut down smooth for me.

Fweasel

iTrader: (6)

My engine shut down issues smoothed out a lot when I installed RS poly motor mounts. Poly motor mounts by themselves are not the cause. How old are your new CS motor mounts? I'm not looking to start a vendor war, but if they were installed by a previous owner, perhaps they've deteriorated from heat despite their age.

Derek5.7

They are new - I installed them about 9 months ago. Yeah, I don't want to start a vendor war either. I think Max at CS is testing a "green" proto-type motor mount that is stiffer than stock/factory but not as stiff as the black and certainly not as stiff as the red.

ls1247

iTrader: (2)

What is your idle speed?

Derek5.7

About 800 rpm

ls1247

iTrader: (2)

I think CS actually shows 3 different motor mounts on their site now....

800rpm sounds about right.

You won't be able to drill holes in the CS trans mount because of all the "structure" that is hidden inside it....ask me how I know this.

I will say that my car is a lot happier with the stock trans mount in it and unfortunately, part of modifying a car can be unmodifying it to get the results you want. I'd start there but before doing anything, recheck all your bolts....

Becker

iTrader: (4)

I also get a bit of vibe shutter on shutdown and have similar mounts. I don't think of it as an issue but some shutdowns are worse than others.

ls1247

iTrader: (2)

Mine will "shuddering" while slight will vary with idle speed which tends to vary a little depending on the weather or whatever else may vary on a 10 year old car with 205k on it. The higher the idle speed, the harder a time it will have shutting down.

juice20

I still get some shudder on shutdown as well. 2005 w/ LS7 clutch/flywheel, CS black motor mounts, tranny mount, and front diff bushing.

BudRacing

iTrader: (3)

Same setup as juice here, minus the trans mount. Mine has some shudder on shutdown as well. It's not as bad as it was before the motor mounts, but still there. There are bigger fish to fry with this car than a little shudder at shutdown. But to answer your question, a softer mount with soften that shudder, but it's really not worth pulling the mounts or spending they money to do so.

ls1247

iTrader: (2)

mine isn't bad but if we could get the idle speed down to 700 or so, it would shut down cleaner. Any way to adjust idle speed on this car or does the computer trump all??

piening2150

iTrader: (1)

Mine shudders too on shutdown. RS motor mounts and trans mount insert, LS7 clutch and single mass FW, RS diff mount and CS diff block. The motor mounts helped, but it has shuddered the whole time I've owned it.

hefftone

Mine is tons better with my 80a poly mounts vs the blown stockers, but I do feel it from time to time. Do I love it,...no...but then I remember I have a badass vette motor in my daily driver so I can live with it!

bmylez

iTrader: (3)

Yep, looks like CS does indeed sell "stage 1" mounts but they are listed as stock replacement and not recommended for modified cars. I wouldn't mind taking some vibes out of my car, but not sure if they would consider my car too far from stock. Hmm...

Becker

iTrader: (4)

I believe Bud is spot on...bigger fish to fry.. If your worried about it potentially weakening or shaking something loose it could happen but same goes for when you smash the accelerator to the floor...

Maybe someday i would consider trying some softer mounts, but I would rather move forward than backwards, if I am going to put any more money into it then it will be upgrades. My car may vibrate a little bit but it also is what I expected.

ls1247

iTrader: (2)

lower idle speed problem solved. anybody know how to do it on this car?

Becker

iTrader: (4)

Hp tuners is the first that comes to mind

Derek5.7

I appreciate your input guys - thanks. In a weird sort of way it is reassuring to know others have a similar problem, especially those of you with a similar set-up to me. Maybe another way of asking the question is, does anyone with black CS motor mounts have a totally quiet engine shutdown? If the answer is yes, then I think it would be worth it to me to pull the mounts out again and re-check torques on all the nuts/bolts. I have a nagging feeling I didn't torque down enough the upper and lower nuts of the connecting the poly mounts to the aluminum brackets (or use locktite) and that this could very well be the source of the shudder on shut-down. So, again, anyone with black CS motor mounts have a quiet engine shutdown with little to no shudder?