(Not) Good Vibrations

[Hoopster]

During the wonderful PCGB Factory Tour trip around Germany, (which I can heartily recommend!) I began noticing mild vibrations in the "lower back" region at around 3500 rpm in each gear. Just before the trip my OPC had done a full fine balance on each wheel and a full geometry set up too, so I am pretty sure it was not related to the wheels or geo.

Today I had an opportunity to take the OPC engineer out for a test drive, to experience the vibrations for himself. He indicated that he thought the cause could be a slight imbalance of a gearbox/engine component e.g. clutch, flywheel...? We also noticed that when the car was at standstill (in neutral) and the drive was not under load, the vibrations occurred around the 2500 rpm mark.

In order to further diagnose, the OPC would now like test for vibrations with the gearbox attached and unattached, thereby hopefully being able to identify if it is clutch related or something else in the engine (flywheel?)

To drop out and test with/without gearbox is a considerable expense, which may or may not be covered by the warranty depending on the outcome (a clutch replacement is wear and tear, an imbalance in the fly wheel would be a fault and thus a warranty claim.)

So I am trying to figure out my risk/reward sum here and would welcome any suggestions & thoughts.

It's a 2007 987 3.4 S, mileage is 36000 (ish).
Does the fact it vibrates in neutral at standstill indicate the likehood that it is not clutch related ?
At what mileages do clutches need replacing ? I do realize this is heavily dependent on driving style, but it is a lightly used car, and I have yet to wear out a clutch on any other vehicle I have owned in 30 years, so 36k feels a bit early.
HAs anyone else experienced mild vibrations as a precursor to a worn clutch ?
I would expect that a flywheel imbalance is not something that develops over time - surely it's either there or it's not from the start?

Your insight and wisdom would be much appreciated !

Adam

 

[Motorhead]

Sorry to hear about your problem Adam. Since the vibration occurs when the vehicle is stationary it's clearly caused by some element(s) in the powertrain assembly, most likely the flywheel or clutch.

If you can discount the problem being caused by a failed component in the engine mounting system then I think that the next port of call will have to be something associated with the flywheel/clutch assembly. Rather than the problem being with the clutch, I would suspect that the dual mass flywheel [DMF] would be a more likely source of the vibration but either way, removal of the transaxle will be required for investigation when both components can be examined.

Jeff

 

[Contraband]

Does it make the same vibration at a standstill with the clutch pedal pressed?

 

[Hoopster]

Thanks for the lateral thinking chaps.
To answer Contraband - yes, the vibrations occur whether or not the clutch is depressed - so I guess that means it's probably not the clutch.

Meanwhile a friend (with a Boxster) had also suggested checking the engine mounts - they can be prone to hardening and cracking around 30-50k apparently... honestly never heard of this before, has anyone else??? But perhaps worth an initial check before a full engine removal.

 

[Motorhead]

Yes Adam, as mentioned in my previous post the engine mounting system components would be my first port of call before attempting to look elsewhere.

The front (engine) mount is a straightforward elastomeric mount but the two rear (gearbox) mounts are fluid-filled (hydro) mounts and it's possible that some fluid has escaped, so it's definitely worth checking the condition of all the mounts.

Depressing the clutch will unload the clutch disc and disconnect the drive to the gearbox, so if the vibration is still present it sounds as though the problem is engine related.

Jeff

 

[Hoopster]

Just got the car back from OPC - engine mounts are all sound, and not the cause of the vibrations. Clearly coming from the engine/gearbox, so further investigations to follow...