Trans is a knockin'

[Driver_X]

I have a knocking sound coming from my transmission. First off, let me say that it operates fine. No problem going into or out of gear, no grinding. No noise (that I can hear) while in gear & under load. The knocking is heard while @ idle, in neutral, with the clutch disengaged. When I push the clutch in, the noise disappears. The knocking is not present when the car is cold, it takes at least 10 minutes of driving for the issue to present it'self.

Recent change to Penzoil gear lube from the blue stuff (recommended by well respected shop in eastern PA) with no change in symptoms, no metal bits found in oil. Rebuilt trans put in by PO 14,000 & 11 years ago. I've been getting around the issue by waiting @ stop lights with the clutch in. Thoughts?

[Daves911L]

Without hearing it, one can't say for certain. But your description sounds to me like standard 915 gear rattle. Completely normal. When there is no load on the gears/shafts the internal bits just rattle harmlessly against each other. Cold oil prevents the rattle, as does loading things up by putting it in gear with the clutch depressed. It makes some people crazy, and others seem not to notice it. Porsche suffered lots of complaints from buyers of new cars with 915 boxes back in the day. Choice of oil can make some difference, but to my knowledge there is no known cure.

[Bob Kontak]

Throw out bearing? Or is that noise the other way around - makes noise when pedal pushed in?

[Driver_X]

Normal would be good news....driving season is coming up :-)

[db_cooper]

Originally Posted by Driver_X

I have a knocking sound coming from my transmission. First off, let me say that it operates fine. No problem going into or out of gear, no grinding. No noise (that I can hear) while in gear & under load. The knocking is heard while @ idle, in neutral, with the clutch disengaged. When I push the clutch in, the noise disappears. The knocking is not present when the car is cold, it takes at least 10 minutes of driving for the issue to present it'self.

Recent change to Penzoil gear lube from the blue stuff (recommended by well respected shop in eastern PA) with no change in symptoms, no metal bits found in oil. Rebuilt trans put in by PO 14,000 & 11 years ago. I've been getting around the issue by waiting @ stop lights with the clutch in. Thoughts?

915 transmissions rattle at idle..fact of life. Porsche tried some additional insulation in the shifter tunnel..it made no difference. A smooth idle with the mixture set and no air leaks makes the transmission pretty quite. The "jumpy" idle from uneven cylinder firing or a mixture that is out of wack makes the rattle worse.

915a all rattle. It is why Porsche went to a all brass synchronized in the G50..its silent.

I would not ride the clutch at idle...it can wear out the release bearing and clutch disc very quickly.

Just make sure the intake gaskets are in good shape and the mixture is set. That really helps.

[Driver_X]

It's my first 911, these responses are reassuring. Thanks guys!