1800RPM vibration mystery

[Bruno]

My 2004 M3 Coupe with 60K miles has recently developed a vibration/shudder right around 1800 rpm. It feels like something in the drivetrain is out of balance and causes a vibration.

This happens in gear, and can be felt while accelerating and decelerating. It's most noticeable when i'm slowing down and my foot is off the gas pedal the revs drop past 1800.

It seems to still be up there even when the car warms. The car is pretty much stock except for the exhaust... Did a scan and no codes came up. Car idles like **** on start up due to the shot MAF sensor and runs perfectly otherwise.

Through the process of elimination, I'm thinking it might be that the flywheel is somehow out of balance. Others have suggested having a look at the clutch...

I’ve already done wheel alignment and balancing so this eliminates the wheels, also changed section 2 of the exhaust and the muffler which also eliminates the exhaust and its rubbers involved. I also checked the guibo and the driveshaft and they seem to be ok.

The only thing left is the clutch and flywheel… can it be?

Any ideas or suggestions as to what this might be?

-Thanks

[Wazif]

U have covered most of the problem points. What about the mountings? did you check the gear/engine mountings?
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[SewerSideUp]

If it it was a mounting, then you'd have a bug thug everytime there is an acceleration or deceleration force. Not such specific vidbration.

Could be your clutch, does it vibrate if you shift to a higher gear at slow speed, i.e. : from 2nd to 3rd at 40km/h ? With shift sensitivity set to lowest ofcourse and easyon the gas. If so, then it most probaby is you clutch .

Other reasons might include, guibo, drive shaft or drive shaft link (cross's).

[RAFiK]

hmmmmm .... bit confusing. Have ur car checked at X-Service Center. oh n btw i called to ask for front Brakes and Rotors (2600Dhs) with wiring but without labor charge. Gonna fix them on saturday !!!

[Ayham]

Physics concept:

When the vibration is related to RPM, it's harmonics to look at, i.e. a rotating part is out of balance.

Flywheel/clutch assembly doesn't cause the car to vibrate. What's left is your drive shaft. The shaft itself is solid, so check the weak points in it. This covers the flex disk "guibo", and the universal joint connecting the two shaft sections.

[SewerSideUp]

There could be one more harmonic part that might be screwed up, the part wich I always hate to mention !
The harmonic balancer also known as the crank pulley. If that's damaged, then youre in for a rough ride. It's pretty expensive, it's hard to find and has a great tendencty to actually damage your crank shaft ! Meaning goodbye motor !

So, get this checked as soon as possible Brunz.

[Bruno]

i don't mind if this particular part get's damaged... schrick cam or strocker FTMFW!

on a more serious note: the car is babied and well taken care of. i really don't push it hard and i don't go over 140km/hr...

[Ayham]

Guibo!! Cranck pulley is remotely likely to fail unless YOU tamper with your engine internals.

[Wazif]

guibo test....

1. drive car downhil at around 20 kmh
2. change to second gear
3. as you approach 40km/h IMMEADIATELY LIFT OFF GAS
4. as the engine braking kicks in, if you hear a click noise, time to investigate further into guibo failure possibility

hope it helps....
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[Bruno]

there is no click or any noises... it's a vibration. it only happens at that level of RPM only when the car is moving. weird eh? i think Neyazi had this exact problem and he changed something in the driveshaft... i anyways i'm not worried, worst case senario it turns out to be the clutch/flywheel and i end up upgrading them but let's hope not cz at the moment i'm broke :S

[NightCrawleR_Z]

see .. i dont know about the M... but maybe its something simler to what i faced,

check your coils.. i faced the same problem between the same range. and it was one of the coils died, and caused missfiring in the cylnder which caused the vibrating on that range...

change the 6 coils all at once. even if only one is damaged, and get your self a grounding kit which will prevent you from this problem in the future and will give u better responce for the gear since you have smg. :)

and u may tell me i did put it on the diagnose system and didnt give any errors. it wont show any error unless its missfiring on the same time you are checking.. the problem you facing is in the early stages where the coil is missfiring sometimes only and trying to force the death :P ( 7alawet erooo7 in arabic :P )

so get it checked and let me know :) good luck buddy