[T3] Moaning in and out of gear

[John Jaranson]

On Jun 27, 2016, at 9:27 PM, Daniel Nohejl wrote:

> Yes, changed the muffler yesterday and it has no bearing on the sound. Are you sure you don’t hear anything? I have tinnitus in both hears and some moderate hearing loss and it’s as plain as day to me. Try earbuds or something?
> 
> A bit more info……when standing behind the car, I can hear the noise when Jessica revs the motor to the rpm the noise emerges at. When I open the hatch, I hear it less, and when I open the engine cover I can barely hear it at all but I can feel vibration/pulsing in the fan housing in synch with the noise. So the full experience of the noise requires everything to be buttoned up so that it can resonate more fully under the cover and in the rear of the car.
> 
> So it would seem to be the fan. It was welded and balanced. My understanding is that the fan is something of a harmonic balancer so perhaps the welding changes how it resonates? Not only were the individual blades welded but the center of the fan was tack welded to the larger outer fan. Am I on to something? If not the fan, perhaps the housing?


The center of the fan and the outer fan are normally joined by a rubber bushing so that it can act as a harmonic damper of sorts.  If you tack welded the center to the outer you have taken away that feature of the fan and it could lead to different or completely new resonances.  You might be hearing on of the new natural frequencies of the welded fan that can't be damped out by the rubber coupling.

BTW, I don't really hear anything funny in the videos you posted.  I just believe that you are hearing something and the welded fan is probably the culprit.

Why did you have it welded?  If this on a high revving stroker motor or something?  With a stock motor, the fan should not need to be welded.  JIll and I just completed a 4000 mile round trip to the Invasion in Arizona in both our Type 3s and regularly saw 75mph+ at about 3800 rpm or more and did not have any issues with the stock, non-welded fan.  Never even occurred to me to think about the fan.  Sometimes, if it ain't broke....don't fix it.

Later,
John Jaranson
www.carartbyjohn.com


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