G$ 993

Hey guys. Something funny is going on with my 4S post clutch repair. Initially during my drives I noticed a very rare vibration from the rear of the car which I attributed to road noise (and perhaps a bit of denial). After driving the car to California and back from Oregon for rennsport there is undoubtedly something going on and its becoming more frequent. On periodic throttle lift deceleration there is a vibration from the rear of the car that feels similar to the rear tires are driving over a rumble strip. I can feel this all the way up through the shifter. I also occasionally note a more mild version of this through the shifter during throttle lift for gear changes. Unfortunately it is not consistently reproducible but seems most frequent in the mid RPM range. I had a standard OEM clutch replaced and the dual mass flywheel was resurfaced. I should also note that the car has RS motor mounts and a FD transmission mount (although these were present before the clutch repair).

Of course, I'll be taking the car back the the shop but was hoping for any ideas you all may have to help guide the process.

Thanks!

pp000830

Did you replace the flywheel?
The reason for the Dual Mass Flywheel in the 993 is to address the engine‘s ignition-induced rotational speed irregularity cause of vibration in the driveline. At certain speeds ignition timing matches the natural vibrations of the driveline amplifying the vibration causing transmission rattle and body boom.
The vibration you are experiencing may be normal and it just seems to be incrementally more noticeable to you now seeing that you describe the issue as " I noticed a very rare vibration from the rear of the car which I attributed to road noise (and perhaps a bit of denial)" If your flywheel was replaced with a new one it may have a slightly different influence on dampening driveline vibration. Also, slight differences in the transmission mounts or engine mounts could influence vibration dampening so if one or more of these were replaced in the process it could influence your issue.
Just some thoughts,
Andy

AOW162435

pp000830

If this is the case I would consider replacing all the CV bolts as they may have been weakened from fatigue due to under torquing.

G$ 993

Thank you for the thoughts guys. The flywheel was resurfaced. Not replaced.

Steve Weiner-Rennsport Systems

Did they balance the clutch & flywheel?

G$ 993

Steve there is no mention of balancing in the invoice.

Top-Gun

Steve,

How important is it that a new flywheel and new pressure plate be balanced as an assembly (rather than trusting that each component is neutral balanced by the manufacturer)? Would an unbalanced flywheel/pressure plate cause a vibration that increases with engine rpm, or would you expect to see vibration only at certain RPMs?

Not to derail the OPs thread, but this may be of help in diagnosing their issue as well. I ask as I questioned this when I installed my MWF and figured not many people would actually send a brand new flywheel and pressure plate to a balance shop before installing. Now that you've mentioned it here it has me questioning it again.

Thanks.

Steve Weiner-Rennsport Systems

Over the years, I've found Sachs pressure plates (and Porsche flywheels) not always well balanced and once in awhile, provide a good shake at higher (>4K) RPM. For that reason I always zero-balance these components whenever I replace a clutch. FYI, zero-balancing allows these components to be replaced without changing the balance of the engine's internals.

It costs a little more, but helps assure a smooth running engine.

G$ 993

To close the loop on this thread, we swapped back to the OEM transmission mount and the vibration went away. Hopefully the OEM mount is not now masking something in the drivetrain!