02 996 Turbo noise
07-21-2014, 07:27 PM
#1
Nordschleife Master
Thread Starter
02 996 Turbo noise
Hello All,
Working on a 996 Turbo here, just a tick over 50k miles.
I made a mistake and did not drive the car before hand so I do not know what all the little noises there were there before I started.
However, I dropped out the transmission and replaced the clutch in the car.
Process went smooth.
I did not lower the engine, I did reach up and and remove the two bolts for the crash brace and pulled it out to pull the engine.
Now the car drives perfectly, clutch operates perfectly. However there is what I would describe as a buzzing sound.
Drove the car after the work and sound wasn't there, or I didn't notice it.
Owner came and got the car 30 min later he came back saying that sound was not there before.
The sound I would describe best as a heat shield buzz.
Sound is not:
Present at idle,
under acceleration,
audible from under car,
does not change when heat shields manually held with screwdriver,
Sound is:
worst under deceleration,
mostly there during cruise but will disappear for a split second to a couple seconds,
there with clutch engaged, and disengaged,
there from 1500-4k rpm (not tested above this),
only audible from inside car appears to be more prominent from rear drivers area,
can reproduce noise blipping the throttle with car on or off hoist.
When I drove the car a second time cold, the noise was almost gone, however I had adjusted the for/aft positioning of the transmission/engine via the transmission mount. Further adjustment have proven to be futile making me believe that it was/is temperature dependent.
Listening with a stethoscope from under the car while noise is present inside car shows no noises from the clutch area. The turbo/valve cover heat shields are all intact, with no bolts/mounts missing/broken. The heat shields bolted to the mufflers are missing a number of bolts, but holding a screwdriver against them has zero effect on the sound inside the cabin.
My thoughts,
due to the fact that the noise disappears under acceleration (at all rpms), I do not believe it to be an engine noise. Due to the fact that I cannot hear it with a stethoscope from the bellhousing I cannot see it being a clutch noise.
But I am a slight bit baffled by where this noise could be coming from.
Any suggestions as to what to check will be most appreciated.
Working on a 996 Turbo here, just a tick over 50k miles.
I made a mistake and did not drive the car before hand so I do not know what all the little noises there were there before I started.
However, I dropped out the transmission and replaced the clutch in the car.
Process went smooth.
I did not lower the engine, I did reach up and and remove the two bolts for the crash brace and pulled it out to pull the engine.
Now the car drives perfectly, clutch operates perfectly. However there is what I would describe as a buzzing sound.
Drove the car after the work and sound wasn't there, or I didn't notice it.
Owner came and got the car 30 min later he came back saying that sound was not there before.
The sound I would describe best as a heat shield buzz.
Sound is not:
Present at idle,
under acceleration,
audible from under car,
does not change when heat shields manually held with screwdriver,
Sound is:
worst under deceleration,
mostly there during cruise but will disappear for a split second to a couple seconds,
there with clutch engaged, and disengaged,
there from 1500-4k rpm (not tested above this),
only audible from inside car appears to be more prominent from rear drivers area,
can reproduce noise blipping the throttle with car on or off hoist.
When I drove the car a second time cold, the noise was almost gone, however I had adjusted the for/aft positioning of the transmission/engine via the transmission mount. Further adjustment have proven to be futile making me believe that it was/is temperature dependent.
Listening with a stethoscope from under the car while noise is present inside car shows no noises from the clutch area. The turbo/valve cover heat shields are all intact, with no bolts/mounts missing/broken. The heat shields bolted to the mufflers are missing a number of bolts, but holding a screwdriver against them has zero effect on the sound inside the cabin.
My thoughts,
due to the fact that the noise disappears under acceleration (at all rpms), I do not believe it to be an engine noise. Due to the fact that I cannot hear it with a stethoscope from the bellhousing I cannot see it being a clutch noise.
But I am a slight bit baffled by where this noise could be coming from.
Any suggestions as to what to check will be most appreciated.
07-21-2014, 07:41 PM
#2
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Do you have any hoses or bracket rubbing on the CV's
Is the driveshaft donuts shot.
Did you look at the tranny mount>the rubber fails cracks at the rubber webbing.
Didn't drop the engine low enough causing uneven support on the mainshaft and you knocked out the front mainshaft bearing>> ala buzzing..
Is the driveshaft donuts shot.
Did you look at the tranny mount>the rubber fails cracks at the rubber webbing.
Didn't drop the engine low enough causing uneven support on the mainshaft and you knocked out the front mainshaft bearing>> ala buzzing..
07-21-2014, 09:25 PM
#3
Race Director
Nothing jumps out at me other than...
Whenever the engine/drivetrain is messed with it is important to get the engine/drivetrain back into their original position. If you do not you can change the vibration dynamics of the car and well, what you hear can be the result.
Check your work. Be sure nothing -- a wiring harness, hose, bracket, anything -- is out of place and possibly touching the body or some other part of the car it was not touching before.
Be sure you have all exhaust brackets/mounts secure and there none of the exhaust system is under extreme tension or compression. You want to avoid having to force an exhaust system to line up and bolt up if at all possible.
Last my Boxster manifested a buzzing like a heat shield noise and the cause proved to be an exhaust manifold with a loose converter brick inside. It was surprisingly loud buzzing too. Sometimes upon a cold start I'd hear a knocking noise that as best I could describe it sounded like a rod bearing knocking or perhaps too much end play in the crank. (Given the car's miles I could believe the engine was wearing out so I resigned myself to just continuing to drive the car until...) However, since I replaced the two stock exhaust manifolds with used ones (though quiet when given the shake test, unlike one of the original ones off my car) I have not heard this knocking noise at all.
Furthermore, even though the brick was loose enough to knock/buzz the converter continued to work just fine, well, at any rate good enough to pass emissions tests here in CA several times, and even though it generated a CEL once in awhile it could go months between consecutive CELs.
Whenever the engine/drivetrain is messed with it is important to get the engine/drivetrain back into their original position. If you do not you can change the vibration dynamics of the car and well, what you hear can be the result.
Check your work. Be sure nothing -- a wiring harness, hose, bracket, anything -- is out of place and possibly touching the body or some other part of the car it was not touching before.
Be sure you have all exhaust brackets/mounts secure and there none of the exhaust system is under extreme tension or compression. You want to avoid having to force an exhaust system to line up and bolt up if at all possible.
Last my Boxster manifested a buzzing like a heat shield noise and the cause proved to be an exhaust manifold with a loose converter brick inside. It was surprisingly loud buzzing too. Sometimes upon a cold start I'd hear a knocking noise that as best I could describe it sounded like a rod bearing knocking or perhaps too much end play in the crank. (Given the car's miles I could believe the engine was wearing out so I resigned myself to just continuing to drive the car until...) However, since I replaced the two stock exhaust manifolds with used ones (though quiet when given the shake test, unlike one of the original ones off my car) I have not heard this knocking noise at all.
Furthermore, even though the brick was loose enough to knock/buzz the converter continued to work just fine, well, at any rate good enough to pass emissions tests here in CA several times, and even though it generated a CEL once in awhile it could go months between consecutive CELs.
07-22-2014, 01:25 AM
#4
Nordschleife Master
Thread Starter
Thank you both for your comments, and thank you Kevin for taking the time to talk to me on the phone.
I have triple checked that all the pieces were properly secured, and there is no issues there. I am going to further inspect all the clutch components and the dual mass flywheel again tomorrow to ensure that I haven't missed anything. All the of the coolant pipes had their proper retainers, and as far as I could tell nothing was out of place.
Kevin,
You have mentioned taking out the front mainshaft bearing (part # 999 110 117 00?) if there was weight being placed on the mainshaft. But given that the bearing is a tapered roller bearing I would find that very difficult to see happening, and while the noise is present under the cabin, the mid section where this bearing resides is completely silent with a stethoscope.
I have however made a video of the buzzing noise
https://www.youtube.com/watch?v=6nHq...ature=youtu.be
It may be hard to tell what the noise is from the video. The engine is only being revved to around 2700rpm in the video. And again, this noise cannot be heard from under the car, only inside the cabin......
If anyone has it I would like to know what the axial measurement possibly is on the transmission input shaft if anyone has that (cannot locate in factory manual). Or if there is another bearing not listed in PET etc that resides behind the shaft seal on the engine side of the differential.
I have triple checked that all the pieces were properly secured, and there is no issues there. I am going to further inspect all the clutch components and the dual mass flywheel again tomorrow to ensure that I haven't missed anything. All the of the coolant pipes had their proper retainers, and as far as I could tell nothing was out of place.
Kevin,
You have mentioned taking out the front mainshaft bearing (part # 999 110 117 00?) if there was weight being placed on the mainshaft. But given that the bearing is a tapered roller bearing I would find that very difficult to see happening, and while the noise is present under the cabin, the mid section where this bearing resides is completely silent with a stethoscope.
I have however made a video of the buzzing noise
https://www.youtube.com/watch?v=6nHq...ature=youtu.be
It may be hard to tell what the noise is from the video. The engine is only being revved to around 2700rpm in the video. And again, this noise cannot be heard from under the car, only inside the cabin......
If anyone has it I would like to know what the axial measurement possibly is on the transmission input shaft if anyone has that (cannot locate in factory manual). Or if there is another bearing not listed in PET etc that resides behind the shaft seal on the engine side of the differential.
07-22-2014, 02:16 PM
#5
Nordschleife Master
Thread Starter
I spoke with Gbox regarding the mainshaft bearing, and they stated that there would be no chance of damaging the bearings. I was able to confirm that all measurements on the box were within spec as well.
Further inspection of the clutch parts, everything shows perfect. The new TOB is not making any noises it shouldn't be. Pilot bearing feels as if it is new.
Further inspection of the clutch parts, everything shows perfect. The new TOB is not making any noises it shouldn't be. Pilot bearing feels as if it is new.
07-24-2014, 12:41 PM
#6
Nordschleife Master
Thread Starter
This has been resolved.
It was a hard line that had popped out of its clip and was ever so slightly touching the body. A slight tweak of the line and it stayed in and noise gone.
It was a hard line that had popped out of its clip and was ever so slightly touching the body. A slight tweak of the line and it stayed in and noise gone.
07-27-2014, 11:29 AM
#7
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Dudes!
I have been having this same phantom noise problem since my clutch was replaced (without pulling the engine)... I have done everything but pull the motor/trans again - can you tell me which line or specific area had come loose? Its at least worth checking on my car!
Thank you!
--Colt
I have been having this same phantom noise problem since my clutch was replaced (without pulling the engine)... I have done everything but pull the motor/trans again - can you tell me which line or specific area had come loose? Its at least worth checking on my car!
Thank you!
--Colt