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Discussion Starter · #1 ·
Yesterday the noise got louder! I’ve checked every part under the vehicle and everything looks good! No play on the exhaust, mounts or any suspension part! My 1st thought was that my driveshaft is unbalanced... Long story short, before I rebuilt my engine I had taken it apart at my moms house and left it on stands, had to get my car from my moms house one day, I had the trans on still and needed to remove the trans for the tow truck to take the car... It’s was a last minute thing, and I forgot to mark the half shaft to driveshaft correlation... So when I got around to putting everything back on, I had no markings to go with in regards to connecting both back on in a balanced state.... From that day I would hear a slight thumping sound at every take off... I bought the car used and undeliverable so I’m not quite sure if the car already had the issue? All that being said would a unbalanced driveshaft cause the loud thumping/knocking/clunking sound? It’s only of take off... Initially your first thought would be that exhaust what’s causing it, based on how hard the sound is... But like I said, the exhaust is tight... I’ve never had a problem with an unbalanced driveshaft... So I don’t have the slightest clue to how one would sound unbalanced?
 

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A defective driveshaft, whether it's unbalanced or has damaged U-joints will cause serious vibrations in the drive line at all speeds. The degree of the vibration depends somewhat on the speed of rotation but suffice to say, it doesn't go away.

If you only hear a clunk on acceleration, then the problem is likely a suspension component such as bushings, hydro bearings, or sway bar links.
 

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Discussion Starter · #3 ·
Yeah, that’s what I thought... It’s not just one thump or clunk, I use to that when I would put my e46 in reverse and that was because of the rear suspension. It’s more like a rattle but deep clunking, sounds like a loose exhaust. I tried to replicate the sound power braking it, but it won’t do it. Also had it on stands rev it on drive still wouldn’t do it. My question is why only on take offs? Don’t hear it after taking off...
 

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Sometimes the failure of a part is not evident by visual inspection. I had defective sway bar links that looked ok but only until I removed one was I able to see that the bearing surface was gone. A similar issue exists with ball joints.

What's the mileage and age of your car?
 

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Sounds like the old center driveshaft support bearing thumping noise that BMWs have been famous for. Does it seem to be right behind you towards the center of the car?

Sent from my XT1635-01 using Tapatalk
 

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Discussion Starter · #7 ·
Sounds like the old center driveshaft support bearing thumping noise that BMWs have been famous for. Does it seem to be right behind you towards the center of the car?

Sent from my XT1635-01 using Tapatalk
Yeah it’s coming directly from under the center of the rear seats... Mileage is 150K 2008... I’m gonna remove the exhaust and heat shield and see what the hell is making the noise? Thanks for the advice!
 

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If the noise is a deep thumping that has some correlation to speed and then goes away once you get up to say 5 mph, it is very much a classic driveshaft center bearing. It will get worse as the rubber bushing around the bearing deteriorates. They can go bad before that mileage if the car is driven hard, but as any rubber bushing part won't last forever.
 

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Discussion Starter · #9 ·
If the noise is a deep thumping that has some correlation to speed and then goes away once you get up to say 5 mph, it is very much a classic driveshaft center bearing. It will get worse as the rubber bushing around the bearing deteriorates. They can go bad before that mileage if the car is driven hard, but as any rubber bushing part won't last forever.
Finally took everything off this weekend and yup! The rubber is completely gone! Question tho, would a unbalanced driveshaft cause this? Or was it just a matter of time for it to get like this?
 

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Yesterday the noise got louder! I’ve checked every part under the vehicle and everything looks good! No play on the exhaust, mounts or any suspension part! My 1st thought was that my driveshaft is unbalanced... Long story short, before I rebuilt my engine I had taken it apart at my moms house and left it on stands, had to get my car from my moms house one day, I had the trans on still and needed to remove the trans for the tow truck to take the car... It’s was a last minute thing, and I forgot to mark the half shaft to driveshaft correlation... So when I got around to putting everything back on, I had no markings to go with in regards to connecting both back on in a balanced state.... From that day I would hear a slight thumping sound at every take off... I bought the car used and undeliverable so I’m not quite sure if the car already had the issue? All that being said would a unbalanced driveshaft cause the loud thumping/knocking/clunking sound? It’s only of take off... Initially your first thought would be that exhaust what’s causing it, based on how hard the sound is... But like I said, the exhaust is tight... I’ve never had a problem with an unbalanced driveshaft... So I don’t have the slightest clue to how one would sound unbalanced?
Finally took everything off this weekend and yup! The rubber is completely gone! Question tho, would a unbalanced driveshaft cause this? Or was it just a matter of time for it to get like this?
I think you have answered most of your own question. If it was me, I would take the shaft somewhere to get balanced. However, maybe there's a source to buy a balanced shaft for cheaper? Then put it all together with a new center bearing.

Looks like even vanilla shops like Meineke offer this.


Also a home test offered here (seems quite unsafe, but here).
 

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There is a strong likelihood that just replacing the center bearing will be fine, but if the history of the car isn't fully known it comes down to do you want to go through this again in 3 months? I went through that on an e28 and finally bought a driveshaft from Driveshaft Specialist, as dukedkt422 recommended. That is THE place for an ultra reliable rebuilt driveshaft without question. A split driveshaft needs to be reassembled by aligning the index marks to preserve perfect balance.


Sent from my SM-T580 using Tapatalk
 

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There is a strong likelihood that just replacing the center bearing will be fine, but if the history of the car isn't fully known it comes down to do you want to go through this again in 3 months? I went through that on an e28 and finally bought a driveshaft from Driveshaft Specialist, as dukedkt422 recommended. That is THE place for an ultra reliable rebuilt driveshaft without question. A split driveshaft needs to be reassembled by aligning the index marks to preserve perfect balance.

Sent from my SM-T580 using Tapatalk
This winter when the Olds goes back under the knife, I'll be placing another order from them for an Al driveshaft to replace my original, 35 year old steel shaft. May even do the same for my '84 GMC, which also has a carrier bearing. Easy way to free up some ponies!
 
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