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Discussion Starter #1
Ok so I get the notorious vibration coming from under my car and start the list of things to check off for possible candidates.

Its not the center drive shaft mount (I just had it replaced)
It not either flex discs (I checked them both while changing CDS)
Its not exhaust mounts (Checked them too)
Its not sway bar brackets or mounts (Checked as well)

The sound is a kind of clunking coming from directly under my right arm and i can even feel it on the arm rest. It happens under load while im driving and also when I hit a bump.
P.s. it get faster with speed which suggests a moving part.

The possibilities left...
Universal mount on the drive-shaft
Rear Transmission mount
Something axle related
Rear diff mount...

Im lost... are any of those on the second list very common?
Thanks in advance
 

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Discussion Starter #3
thats the flex disc I was talking about. I checked both of them and they are both ok...thanks though
 

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thats the flex disc I was talking about. I checked both of them and they are both ok...thanks though
OK, I will admit to my ignorance. I am only aware of one flex disc, up at the front of the driveshaft. Where is the second??hmmm
Regards,
Jerry
 

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Discussion Starter #6
there is one between the transmission and driveshaft and I thought I saw a possible second one between the driveshaft and diff... May be mistaking
 

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It would be helpful when posting questions like this to include the mileage on the beast. I would suggest that it sounds like driveshaft universal joint problems.

Take it to a good shop that can put it up on the lift and diagnose it properly for you.

Michael
 

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I am having a similar problem but mine is not drive shaft related because I only get a thud when going over a bump which sometimes can be felt through the armrest. Like you I have checked everything possible and replaced parts which me and my mechanic were sure was the cause.
 

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Discussion Starter #10
Right ...its sooo annoying. I have a 50K+ beast so these rubber parts are showing it. Richie rvf, I actually saw those rubber bushings while i was under there and they looked to be a bit collapsed or sort of tilted to the right permanently. Im gonna replace those and the rear tranny mounts, then Ill give updates.
 

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You didnt mention why you had the center bearing replaced? If it was b/c of this problem and it didnt fix it, then you may have a bad driveshaft causing premature failure of the center bearing. Driveline is a company that has a good reputation for rebuilding BMW driveshafts, plus they have a great warranty. Also, check your tranny mounts.

If you have access to a good safe lift you can run the car in the air and look to see what is moving...an out of balance rear wheel can mimick this symptom.
 

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You didnt mention why you had the center bearing replaced? If it was b/c of this problem and it didnt fix it, then you may have a bad driveshaft causing premature failure of the center bearing. Driveline is a company that has a good reputation for rebuilding BMW driveshafts, plus they have a great warranty. Also, check your tranny mounts.

If you have access to a good safe lift you can run the car in the air and look to see what is moving...an out of balance rear wheel can mimick this symptom.
beat me to it
 

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Discussion Starter #13 (Edited)
hmmm...Its just so many things. Im gonna get the car up on a lift soon to check everything out. Im also gonna check the motor mounts later tonight. It could possibly be a motor mount being that I only hear the sound when I hit a bump or the engine is under load. I will report back.

P.s. I replaced the center mount as a preventative measure not for any reason specific.
 

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+1 on differential mounts... I had the same issue. Read here. See post #17.
 

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not to keep harping on the center bearing....but did the problem show up after you replaced it? When the driveshaft is split in two you have to score it to make sure it goes back together the same way or it will be out of balance. It also has to be properly aligned. Up until recently the center bearing required a few mm's of preload when installed. I noticed in the m5 tis that they dont require the preload any longer. Perhaps it wasnt installed properly. Personally I dont touch the bearing unless it shows some sign of a problem. Keep us posted.

One other thing, check the exhaust hanger that has the bars going back to the rear wheels is assembled corectly. if the exhaust got bent at all when it was removed for the center bearing, it may be hiting the driveshaft during acceleration.
 

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Discussion Starter #17
a good possible dignosis but the center moutn was replaced as a result of this problem. It didnt change anything at all. At least I dotn have to worry that it could be the center mount. Im eliminating 1 thing at a time. The driveshaft was scored on both sides to match perfectly as I know the driveshaft is factory balanced.
 

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i had similar issue- it was an issue with the cat converter...it somehow had gotten pushed in and was going thud against the underside of the car/center mount when going over bumps...it was replaced for a couple k and the issue went away...
 

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Discussion Starter #19
I feel that its something driveshaft related though because it gets faster with speed and happens more under load. So I'm thinking maybe a broken tranny or motor mount because under load either one of those could cause the exhaust to hit against the rotating driveshaft but I'm really never gonna know until I get under their again and take a real good look.
 

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Did you read my post? Your symptoms sound spot on to my problem. The failed differential mounts caused damage to my cv joint and driveshaft - both had to be replaced. Good luck.
 
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