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      06-17-2012, 11:57 PM   #1
Superfly_M3
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Thump noise coming from drivedrain under throttle change

Hi Guys,

Perhaps I'm being super anal about this, perhaps it is normal, but here's whats happening:

This happens in all the gears (I've tried 2nd, 3rd, 4th, 5th, and 6th) and only above 3,000rpm or so. I first noticed this on the highway and continued to diagnose the same issue in other gears. Below 3,000rpm it does not "thump" because the motor doesn't have much torque.

While driving at 120-130km/h (75 - 80mph) I would let off the throttle completely. After a second or two I would WOT. What follows is a feeling of somone hitting the rear differential with a sledge hammer accompanied with acceleration. If I let off the throttle and WOT in less than 0.5 seconds, it doesn't do that because the engine doesn't build full vaccuum. It only happens after 1-2 seconds of engine braking. It is more evident with higher rpms.

I've heard rhumors that this could be a "broken diff bolt". I looked under the car from the rear, the bolts seem to be in place (or am I not looking at the right place).

In any case, I will take my car to the dealer to have them look at it, but I just wanted to know if this is normal

Thanks in advance for inputs.
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      06-18-2012, 11:41 AM   #2
Moxie
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If you saw the post below, you gotta be under the car to see if the bolt broke. http://www.m3post.com/forums/showthread.php?t=706124

2011, crawl under it or take it to the dealer.
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      06-19-2012, 12:11 AM   #3
Superfly_M3
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Thanks for pointing me in the right direction.
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