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Rear Clunk

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Old 07-17-2012, 04:27 PM   #1
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Default Rear Clunk

I think something (either a bushing or a shock) may be going on the passenger rear side of the car. When I hit bumps on that side, I get a "thunk" or "whack" sound instead of a dull thump. Any idea what that might be? I've looked everywhere for loose fittings--everything is bolted down tight.
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2006 CTS-V - 422 RWHP/383 RWTQ/3795 lbs - Complete Mod List
- G-Force 9" IRS with PST 3.75" carbon fiber driveshaft and 35 spline axles
- Strange Engineering S-Trac with Pro Iron case and 3.50 ratio
- KW Variant 3 with Swift 120/160 springs, Banski RSMs, Custom FK LSMs
- 5-lug 19x11/20x12" Forgestar F14s, KRC adjustable power steering
- RacingBrake 355/365mm 2pc rotors, ET800 pads, CTS-V2 calipers
- McLeod RXT, Custom McLeod 1373, Comp TRuTorq L3 cam
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Old 07-17-2012, 05:34 PM   #2
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See if one corner is sitting higher than the other if so shocks.
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Old 07-17-2012, 09:21 PM   #3
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Quote:
Originally Posted by Dmax/04V View Post
See if one corner is sitting higher than the other if so shocks.
Would it be a small amount? Because the questionable side does sit a fraction of an inch lower.
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2006 CTS-V - 422 RWHP/383 RWTQ/3795 lbs - Complete Mod List
- G-Force 9" IRS with PST 3.75" carbon fiber driveshaft and 35 spline axles
- Strange Engineering S-Trac with Pro Iron case and 3.50 ratio
- KW Variant 3 with Swift 120/160 springs, Banski RSMs, Custom FK LSMs
- 5-lug 19x11/20x12" Forgestar F14s, KRC adjustable power steering
- RacingBrake 355/365mm 2pc rotors, ET800 pads, CTS-V2 calipers
- McLeod RXT, Custom McLeod 1373, Comp TRuTorq L3 cam
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Old 07-17-2012, 10:12 PM   #4
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Is the questionable side shock oily?
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Old 07-17-2012, 10:19 PM   #5
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Quote:
Originally Posted by BudRacing View Post
Is the questionable side shock oily?
No, but this issue has been occurring for months.
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2006 CTS-V - 422 RWHP/383 RWTQ/3795 lbs - Complete Mod List
- G-Force 9" IRS with PST 3.75" carbon fiber driveshaft and 35 spline axles
- Strange Engineering S-Trac with Pro Iron case and 3.50 ratio
- KW Variant 3 with Swift 120/160 springs, Banski RSMs, Custom FK LSMs
- 5-lug 19x11/20x12" Forgestar F14s, KRC adjustable power steering
- RacingBrake 355/365mm 2pc rotors, ET800 pads, CTS-V2 calipers
- McLeod RXT, Custom McLeod 1373, Comp TRuTorq L3 cam
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Old 07-17-2012, 11:43 PM   #6
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passenger rear always sits lower.

what shocks are you running?
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Old 07-18-2012, 12:10 AM   #7
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Quote:
Originally Posted by Cadzilla View Post
passenger rear always sits lower.

what shocks are you running?
FG2s. I have the Ground Control bushings set to the exact same height, measured with a caliper.

I was thinking about picking up a set of K-Sport coilovers to replace the stock FG2s. Any thoughts? I'm unwilling to spend $2,400 on a set of KW Variant 3's. If the K-Sports are an upgrade over the FG2s, it'd be nice to know. I think their springs aren't as stiff as mine, but they have spherical upper mounts.

Edit: Scratch that--I don't think they have spherical upper mounts. Damn.
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2006 CTS-V - 422 RWHP/383 RWTQ/3795 lbs - Complete Mod List
- G-Force 9" IRS with PST 3.75" carbon fiber driveshaft and 35 spline axles
- Strange Engineering S-Trac with Pro Iron case and 3.50 ratio
- KW Variant 3 with Swift 120/160 springs, Banski RSMs, Custom FK LSMs
- 5-lug 19x11/20x12" Forgestar F14s, KRC adjustable power steering
- RacingBrake 355/365mm 2pc rotors, ET800 pads, CTS-V2 calipers
- McLeod RXT, Custom McLeod 1373, Comp TRuTorq L3 cam

Last edited by FuzzyLog1c; 07-18-2012 at 12:59 AM..
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Old 07-18-2012, 09:02 AM   #8
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Quote:
Originally Posted by FuzzyLog1c View Post
Would it be a small amount? Because the questionable side does sit a fraction of an inch lower.
If it's negligible I wouldn't pin that as your problem, I just mentioned this because I saw my drivers side rear sists an inch lower than my ps rear. find a bumpy road and drive over some bumps with one rear wheel, and keep the other wheel on flat ground and compare the results after doing so with both sides.
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2004 CTS V- More mods than FuzzyLogic- SOLD
2006- CTS V- Infrared and Bone Stock- SOLD
1996- Eldorado- Took 7 cows to make the interior- SOLC
07 GSXR 600- Death Trap 1.0- SOLD
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Old 07-18-2012, 10:43 AM   #9
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Quote:
Originally Posted by Dmax/04V View Post
If it's negligible I wouldn't pin that as your problem, I just mentioned this because I saw my drivers side rear sists an inch lower than my ps rear. find a bumpy road and drive over some bumps with one rear wheel, and keep the other wheel on flat ground and compare the results after doing so with both sides.
Already done. RR makes a nasty clackity sound on short, sharp transients. Left side is a nice, dull thump. Common mode transients (like speed bumps) sound the same sound. RR rides about 1/3" lower than the RL wheel, regardless of conditions.
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2006 CTS-V - 422 RWHP/383 RWTQ/3795 lbs - Complete Mod List
- G-Force 9" IRS with PST 3.75" carbon fiber driveshaft and 35 spline axles
- Strange Engineering S-Trac with Pro Iron case and 3.50 ratio
- KW Variant 3 with Swift 120/160 springs, Banski RSMs, Custom FK LSMs
- 5-lug 19x11/20x12" Forgestar F14s, KRC adjustable power steering
- RacingBrake 355/365mm 2pc rotors, ET800 pads, CTS-V2 calipers
- McLeod RXT, Custom McLeod 1373, Comp TRuTorq L3 cam
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Old 07-18-2012, 01:22 PM   #10
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Quote:
Originally Posted by FuzzyLog1c View Post
Already done. RR makes a nasty clackity sound on short, sharp transients. Left side is a nice, dull thump. Common mode transients (like speed bumps) sound the same sound. RR rides about 1/3" lower than the RL wheel, regardless of conditions.
Unless something is loose, or you can see a bad bushing/mount I would definetly say shock.
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2008 GMC 2500 Duramax CCSB- 0-60 in 5.5 with a Mastercraft in tow... 0-60 in 4.2 unloaded- SOLD
2004 CTS V- More mods than FuzzyLogic- SOLD
2006- CTS V- Infrared and Bone Stock- SOLD
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Old 07-24-2012, 12:03 AM   #11
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endlink probably. unless your sway bar bushing is just shot.

tighten up both ends of that endlink good...especially the bottom. Be sure to use an allen wrench on the bolt to hold it while you use a regular wrench or gear wrench. Sometimes they seem tight even when you use a socket. To test, unload the suspension and hit upward on the bar, it should reproduce the noise if that's it..

could be a loose shock mount or other stuff too but try that first. make sure the spring isn't crooked when you lower the car too. sometimes it doesn't sit on that perch right
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Old 07-24-2012, 07:53 AM   #12
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Found it on Sunday.

Turns out driving-related bumps/vibration had slowly unscrewed the top shock mount nut. Apparently I didn't tighten it down well enough when I applied the Feffman fix.

The tricky part about this one was that the shock nut looked and *felt* tight with the small crescent wrench I could get on it in the car. When I pulled both shocks out and compared them, it was obvious that one of them wasn't torqued all the way down. A couple of turns with a 15mm gear wrench solved that problem.

Everything's nice and quiet now. Thanks, everyone.
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2006 CTS-V - 422 RWHP/383 RWTQ/3795 lbs - Complete Mod List
- G-Force 9" IRS with PST 3.75" carbon fiber driveshaft and 35 spline axles
- Strange Engineering S-Trac with Pro Iron case and 3.50 ratio
- KW Variant 3 with Swift 120/160 springs, Banski RSMs, Custom FK LSMs
- 5-lug 19x11/20x12" Forgestar F14s, KRC adjustable power steering
- RacingBrake 355/365mm 2pc rotors, ET800 pads, CTS-V2 calipers
- McLeod RXT, Custom McLeod 1373, Comp TRuTorq L3 cam
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Old 07-24-2012, 07:53 AM
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