901 gear rattle or clutch issue?

[smiles11]

I’ve noticed some increased chatter when the car is at idle with the clutch engaged (foot off the pedal). Goes away when pressing the pedal. Performance has been great & nothing of note over the last 4k+ miles other than increased chatter. Is this the throw out bearing going bad or do I just have some rattling gears?

https://youtube.com/shorts/MzWCT5OOjks?feature=shared

[edmayo]

Sounds like the throwout arm rattling. Get under the car with the engine running and put your hand on the throwout arm and see if you feel the rattle.

[smiles11]

Thanks Ed. One thing to note. The rattle is only apparent after the car gets up to full operating temps. At initial startup, like in the morning, the rattle is non-existent. Would that eliminate the possibility of it being clutch related or the throwout arm?

I’m gonna go check it just in case though. See if there is any play. Maybe a worn out pivot bushing. Idk

[gled49]

More like main-shaft bearing in the trans, very common problem in the old days, don’t see that much anymore.

[smiles11]

If it is the main shaft bearing.. Is car okay to drive?

I was always under the impression the main shaft bearing will whine more as you rev. Mine doesn’t increase any noise at speed… I was thinking it could be the input‑shaft bearing since it rattles when free‑spinning (clutch engaged) and calms when pressing the pedal.

I’m scheduled to have a stethoscope inspection Monday to see where it’s coming from.

[larwik]

Isn't this similar to what I have been told since "childhood" that it's probably from the gears rattling on the main shaft when under "No Load"?...also that it is the reason I always press the clutch pedal when turning the engine off = No Rattle...if not, it rattles during the last few revolutions and it just sounds awful...I understand it doesn't hurt anything, but I just can't stand the Noice /sound...same for my 901, 915 and G50 transmissions...It works for me and I'm too old to change so I guess I'll continue with my "turn-off" routine...

[smiles11]

More like main-shaft bearing in the trans, very common problem in the old days, don’t see that much anymore.

Also curious, why was it common in the old days but not as much anymore?

[gled49]

Not sure if there was a material problem with the bearing or if people just drove them more when they were new. If the bearing is breaking up it creates a shimmer in the oil when drained. There isn’t any short term danger in using the car.

[Jon B]

It's common in older Porsches to get a slight rattle from the transmission when idling.
I'll add that after decades of use, these input shafts usually have some degree of runout, often more than 0.1 mm, and that slight wobble will also create bearing rattle when not under load.



Jon B.
Vista, CA