Hello Group,
I recently had major mechanical work done on my 120K miles M3. My car is a SMG to 6MT swap by the previous owner. I had the car recoded by EAS for the 6MT swap after I purchased it. The bell housing machining and other details were verified by the shop that did my clutch job and they confirmed everything was done correctly. I had no faults or strange noises before I dropped the car off. The shop that did my work specializes in Porsches and BMW's and builds track cars. They are a reputable shop from my research and had glowing recommendations. I am intentionally withholding the shop's name as they have worked diligently to identify the issue and I don't want to throw them under the bus in any way...
In terms of mechanical work, I addressed "Big 3", new Vanos exhaust hub, new OEM clutch with dual pass flywheel, new guibo, engine mounts, suspension bushings, differential bushings, belts, plugs/packs....etc The goal was to address all the major points of failure and any deferred maintenance from the previous owners. I also had an Auto Solutions 20% SSK installed, along with a Magnaflow catback exhaust (don't judge me....I am a fan of the sound and it was an economical upgrade to my rusty/dusty OEM system).
During my first test drive, I heard a rattling sound coming from behind the dashboard down by where the cigarette lighter is. As the RPM's in the car climbed up, the rattle got louder. The car did not make the rattling noises at similar RPM's in neutral. It only makes the sound when the car is in gear as I am accelerating. The rattling is faint and starts at 2500 rpms and gets progressively louder with 5000 rpms being the highest I've revved as I break in my new rod bearings. It sounds like a baseball card hitting a spoke on a wheel. I am hoping to record a video and upload it tomorrow.
I took the car back to the shop and they kept it for an extra week to troubleshoot the issue. They came back with 2 possible theories for the source of the rattle after double-checking their work.
Theory 1 - my catalytic converter may be on its way out. One of my cats has a honeycomb material that has may have come loose resulting in the material moving around inside the cat. They stuck a flathead screwdriver up the cat and could move the honeycomb material. I recently purchased OEM EU headers and Sect 1 as I assume my cats are due for failure and will need to be replaced. No error codes or CEL’s despite the dislodged honeycomb material at this time. No rattling noise when I rev the engine in neutral from 2500-5000 rpms
Theory 2 - the rear output shaft bearing has gone bad or is on its way out. I have a small oil leak by the rear output shaft bearing seal. The shop removed the foam insulation and rubber boot on my shift knob to listen for the noise during a test drive and believe they hear the rattle down by the gearbox. I did some research and saw input & output shaft bearings are a point of failure for SMG to 6MT swaps.
Has anyone experienced a similar rattling issue with the car in gear after replacing a clutch / flywheel? Any recommendations you have for things to verify / double-check would be much appreciated. I plan on taking the car to a transmission shop in a few weeks to get that checked out. I may also take the car to another shop that specializes in E46's to get a second option/fresh set of eyes on the issue.
Thanks in advance for your input.
EDIT:
Thank you all for your input. I sincerely appreciate it. I took a couple videos tonight. I hope these are helpful.
1. Cold start, kept it under 3000 RPM's while the car warmed up. No rattle whatsoever. The rattle begins as soon as the car reaches operating temperatures. Youtube defaulted to upload this as a short... apologies for the format.
2. Car is warmed up and in 3rd gear. The sound is the loudest around 5000 RPM's. I kept it at 4K and dropped the phone down by my knee (adjacent to the cigarette lighter / gear box area I mentioned earlier).
Some edits/revisions I want to make to my initial post. The rattle noise is the same with the car in gear, in gear with the clutch pushed in, and quieter when the car is rolling/revving in neutral but still very much present. I was cruising at 40 MPH in 3rd gear around 4000 and the noise was loud and clear. Pushed the clutch in while still in gear, same noise volume. Shifted the car out of gear into neutral with the clutch released and held the RPM's near 4000 while coasting - sound was present, but quieter.
At this juncture, I believe it is the honeycomb in the headers. I am open to any recommendations or considerations you all may have. If the honeycomb in your headers failed and you heard this noise, please chime in!
I recently had major mechanical work done on my 120K miles M3. My car is a SMG to 6MT swap by the previous owner. I had the car recoded by EAS for the 6MT swap after I purchased it. The bell housing machining and other details were verified by the shop that did my clutch job and they confirmed everything was done correctly. I had no faults or strange noises before I dropped the car off. The shop that did my work specializes in Porsches and BMW's and builds track cars. They are a reputable shop from my research and had glowing recommendations. I am intentionally withholding the shop's name as they have worked diligently to identify the issue and I don't want to throw them under the bus in any way...
In terms of mechanical work, I addressed "Big 3", new Vanos exhaust hub, new OEM clutch with dual pass flywheel, new guibo, engine mounts, suspension bushings, differential bushings, belts, plugs/packs....etc The goal was to address all the major points of failure and any deferred maintenance from the previous owners. I also had an Auto Solutions 20% SSK installed, along with a Magnaflow catback exhaust (don't judge me....I am a fan of the sound and it was an economical upgrade to my rusty/dusty OEM system).
During my first test drive, I heard a rattling sound coming from behind the dashboard down by where the cigarette lighter is. As the RPM's in the car climbed up, the rattle got louder. The car did not make the rattling noises at similar RPM's in neutral. It only makes the sound when the car is in gear as I am accelerating. The rattling is faint and starts at 2500 rpms and gets progressively louder with 5000 rpms being the highest I've revved as I break in my new rod bearings. It sounds like a baseball card hitting a spoke on a wheel. I am hoping to record a video and upload it tomorrow.
I took the car back to the shop and they kept it for an extra week to troubleshoot the issue. They came back with 2 possible theories for the source of the rattle after double-checking their work.
Theory 1 - my catalytic converter may be on its way out. One of my cats has a honeycomb material that has may have come loose resulting in the material moving around inside the cat. They stuck a flathead screwdriver up the cat and could move the honeycomb material. I recently purchased OEM EU headers and Sect 1 as I assume my cats are due for failure and will need to be replaced. No error codes or CEL’s despite the dislodged honeycomb material at this time. No rattling noise when I rev the engine in neutral from 2500-5000 rpms
Theory 2 - the rear output shaft bearing has gone bad or is on its way out. I have a small oil leak by the rear output shaft bearing seal. The shop removed the foam insulation and rubber boot on my shift knob to listen for the noise during a test drive and believe they hear the rattle down by the gearbox. I did some research and saw input & output shaft bearings are a point of failure for SMG to 6MT swaps.
Has anyone experienced a similar rattling issue with the car in gear after replacing a clutch / flywheel? Any recommendations you have for things to verify / double-check would be much appreciated. I plan on taking the car to a transmission shop in a few weeks to get that checked out. I may also take the car to another shop that specializes in E46's to get a second option/fresh set of eyes on the issue.
Thanks in advance for your input.
EDIT:
Thank you all for your input. I sincerely appreciate it. I took a couple videos tonight. I hope these are helpful.
1. Cold start, kept it under 3000 RPM's while the car warmed up. No rattle whatsoever. The rattle begins as soon as the car reaches operating temperatures. Youtube defaulted to upload this as a short... apologies for the format.
2. Car is warmed up and in 3rd gear. The sound is the loudest around 5000 RPM's. I kept it at 4K and dropped the phone down by my knee (adjacent to the cigarette lighter / gear box area I mentioned earlier).
Some edits/revisions I want to make to my initial post. The rattle noise is the same with the car in gear, in gear with the clutch pushed in, and quieter when the car is rolling/revving in neutral but still very much present. I was cruising at 40 MPH in 3rd gear around 4000 and the noise was loud and clear. Pushed the clutch in while still in gear, same noise volume. Shifted the car out of gear into neutral with the clutch released and held the RPM's near 4000 while coasting - sound was present, but quieter.
At this juncture, I believe it is the honeycomb in the headers. I am open to any recommendations or considerations you all may have. If the honeycomb in your headers failed and you heard this noise, please chime in!
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