370Z Annoying Rear Clunk

FrankEtier

Hi Guys! My '14 370 with 49K on the clock started to develop an annoying low speed, under 30mph "clunk" coming from the rear of the car. Mainly noticed when driving on concrete roads with spaced expansion joints. This started after I installed Eibach lowering springs and still remained after switching to KW V1 Coilovers. The only other rear suspension mods are SPL camber arms and Z1 Subframe collars.
Yesterday I did the following trying to determine the source of the noise:
- Removed everything from the rear of the car. Jack, Spare Tire, Bose Sub, Styrofoam fillers, etc. and drove around neighborhood. Low Speed Clunk remained.
-While driving around neighborhood I opened the rear hatch just to see if the latch mechanism could be the source of the clunk. No luck, driving low speed with rear hatch opened the clunk remained.
-Went back home and put car on jack stands and checked every rear suspension bolt for proper torque. Found nothing loose or anything that appeared worn. Drove car again and low speed clunk remained.

I've determined the clunk could be something behind the rear bumper but not on the interior of the car. Or this could just be a noise I'm going to have to live with, price of a lowered car with subframe collars and performance parts and 30 series rear tires.

Has anyone experienced anything similar to this? If so what did it turn out to be? Any ideas of something else to check would be appreciated or just telling me to suck it up and live with it would be welcome also.

Thanks

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‘14 Topgunz Speedworks Rotrex Supercharged VR30 7AT 370Z Magma Red.
@liquid.magma

Spooler

Check your diff bushings. If you see a black streak running down the diff, the rear factory liquid filled bushing is done and needs to be replaced.

FrankEtier

Checked and no signs of failure. The clunk is not related to on/off throttle it strictly occurs when hitting bumps in the road.

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‘14 Topgunz Speedworks Rotrex Supercharged VR30 7AT 370Z Magma Red.
@liquid.magma

Spooler

Did you check your pre-load on your coilovers? That's when you jack the car up under the spring bucket while the car is sitting on jackstands in the rear. You should jack up 1/2in. before the car starts to lift off the jackstand.

Spooler

If you have more than that, then you need to shorten your shock length. It will cause a clunking in the rear if the suspension extends too far. The rear spring becomes too loose in the spring perch/bucket. That's the clunk.

Spooler

You won't see this type of an issue from the front so much. Just the rear because we have a divorced spring/shock setup.

Averying

End links? Those tend to clunk pretty good when they’re bad. My fronts clunk like mad right now. Thanks hotchkis bar


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2009 Sport Touring | Platinum Graphite | GTM Stage 1 Supercharger | BC BR Coilovers | Hotchkis Swaybar | Z1 FUCAs | AME TM-02 Wheels | Z1 2-piece Front Rotors | Z1 Clutch & Flywheel | Invidia Gemini Catback | GTM Resonated Test Pipes

Spooler

Mine can make some noise too but it has to be on a damn bumpy road. Normal road or normal bumpy road, not a peep.

FrankEtier

I’ll check this. Thanks. The car made the noise before the KW coilovers on Eibach lowering springs.

__________________
‘14 Topgunz Speedworks Rotrex Supercharged VR30 7AT 370Z Magma Red.
@liquid.magma

Averying

Lowering the car may have put the end links at a non-ideal angle, wearing them out faster. Just a guess… or they’re simply old and tired?. U can try disconnecting one end link in the rear and see if the noise isn’t as bad. This takes the load off the rear bar.

For the rear preload, jack up the rear and let the car sit at full droop. See if the spring can move at all. It should be compressed 5-10mm at full droop.


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__________________
2009 Sport Touring | Platinum Graphite | GTM Stage 1 Supercharger | BC BR Coilovers | Hotchkis Swaybar | Z1 FUCAs | AME TM-02 Wheels | Z1 2-piece Front Rotors | Z1 Clutch & Flywheel | Invidia Gemini Catback | GTM Resonated Test Pipes

FrankEtier

Thanks! I'll check that out also.

__________________
‘14 Topgunz Speedworks Rotrex Supercharged VR30 7AT 370Z Magma Red.
@liquid.magma

FrankEtier

Jacked car up with both sides rear suspension at full extension. Tried to move the coils, both sides are tight. Can move them at all.

__________________
‘14 Topgunz Speedworks Rotrex Supercharged VR30 7AT 370Z Magma Red.
@liquid.magma

filip00

Is there a chance you can film the clunk sound? I'm wondering if it appears by specific RPMs, what sort of clunk or frequency of clunks it is...

FrankEtier

I only notice the "Clunk/Rattle" on low speed concrete roads with evenly spaced joints. On smooth asphalt roads I don't hear the noise.

I'm thinking it is something in the car behind the interior plastic trim pieces in back of the car. I've checked all the suspension parts and can't find anything loose or seemingly worn. Car only has 49K miles. Thought maybe it was the rear hatch rattling but the rear hatch is tight and when closed has no excessive movement. Drove around my neighborhood with the hatch open and the noise is still there so that kind of eliminates the hatch...

__________________
‘14 Topgunz Speedworks Rotrex Supercharged VR30 7AT 370Z Magma Red.
@liquid.magma

filip00

I would take a rubber hammer and smack literally everything I can see in the car. Starting with the interior - rear strut, sides, panels covering the hatch, rear tire or subwoofer, everything. Then I would lift the car on a lift and do the same on the undercarriage. EVERYWHERE. It might take you about 15-20mins, but I think that you might find the culprit that way.