rosco28

Could you guys give this a listen? Any ideas as to what this noise might be coming from?

It seems to mainly appear when the car is decelerating, either via braking or natural revs slowing the car during coasting. The noise only shows up while I'm driving. When sitting at idle, I can rev the engine without any problem, the engine sounds nice and strong and decelerates normally. There doesn't seem to be any performance loss as a result, but obviously I don't feel comfortable driving the car until this is fixed.

I sent in the car last week to the shop via tow, and when i showed we drove for at least 30 minutes together, then I continued for another 30 minutes without my mechanic sure that the sound would return, but it didn't. Of course now that i have the car back home the sound returns.

So do you guys have any ideas??


Thanks in advance!

rosco28

Come on guys, 33 views and no replies?

This is a 1979 911sc...

APPLtrader

Beats me.

Mark Salvetti

You're talking about that knocking sound that shows up a few times in your audio clip?

Have you tried letting out the clutch when it happens on deceleration to see if the noise goes away?

Since it only happens when you are moving, seems you should focus on CV joints or the transmission. But I really have no idea what it could be.

Mark

rosco28

Pete Z. has given me some ideas which i'll be checking out this week.

Mark - Yes, the knocking which occurs mainly during deceleration. However, when i press the clutch it seems to go away, when i let it out is when it shows up... It can even happen when rolling in neutral so I don't think it's the tranny.

Any other ideas are welcome, in fact encouraged...!!


Thanks!

Mark Salvetti

Don't forget that even when in neutral and the clutch is in, the main shaft is spinning. And if the clutch is out all that means is the transmission is not connected to the engine. But if the car is rolling, the ring gear is turning, and it is therefore driving the pinion shaft. Plenty of stuff spinning around inside the gearbox if you are rolling.

I found a similar "knocking" sound thread on Pelican, and Pete had some ideas for that too. Hopefully he's got you on the right track.

Mark

rosco28

Mark, can you send me a link to the Pelican thread??

Mark Salvetti

It's this one, although now I'm not sure how relevant it is to your problem:
http://forums.pelicanparts.com/porsc...g-tapping.html

Google "911SC knocking sound on deceleration", and you'll get a few more hits.

Mark

ibeaudoin

Is the sound following engine or wheels rev speed?
If you decelerate at 60 mph, engine turning at 3k does it make the same sound as it you decelerate from 30 mph at 3k rpm.
Try to see if it's in sync with the engine or wheel.

rosco28

Hi Ian,
The sounds is in sync with the engine/tire speed. What are you thinking??