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Old 09-01-2010, 06:20 PM   #1
dzenno
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Question Thump on "up"shifts from rear after Wavetrac LSD install?

I'm experiencing a thump from the rear since I got the stock open diff replaced with a Wavetrac LSD. The thump happens strictly on upshifts only. There's no other noises whatsoever. The thump sounds like something hitting the floor in the trunk and it happens on any "up"shift ONLY AS THE SHIFTER IS BEING MOVED INTO GEAR. So, nothing to do with the clutch engagement/disengagement. I can press down on the clutch (disengage it) and while the car is coasting down say 50-60km/hr I can just move the shifter through the gears and on any "up"shift (neutral to 1st, 1st to 2nd, 2nd to 4th....NOT on downshifts) it'll thump in the rear...

There's ZERO noises once the car's already IN gear no matter how you drive it. Car's a 2008 E90 335i 6MT. Since the LSD's been installed I also installed a new 6 puck ceramic clutch and single mass flywheel, the same clunk is still there.
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Old 09-02-2010, 12:51 AM   #2
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Here's a funny thing I noticed that might help shed some light on the cause of this thump from the rear...when I'm shifting and I don't push the clutch pedal ALL the way down but go down so that the clutch basically just disengages so that the gear can be upshifted there's NO NOISE ?

The other interesting thing, not sure if I mentioned earlier, is if I speed up into upshifts and shift higher up in the RPMS (say around 4000 RPM) the thump is next to none or none...

any ideas?
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Old 09-02-2010, 07:32 AM   #3
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Does it make the thump while the car is not moving and off, while trying to move the gears?

Get a mechanic to put it on a hoist while you sit inside and make the noise. Should be easy to pin point if you can consistently make the thump.
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Old 09-02-2010, 09:23 AM   #4
dzenno
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You'd have to get the car to roll a bit back and forth to reproduce it consistently...when stopped it just happens the very first time you upshift, not after, unless you roll the car back and forth a few inches and then do it..
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N54 6MT TwinTurbo 60-130mph World Record: 6.5sec 100-200km/hr, 7.5sec 60-130mph (vbox verified)
N54 (ACN 91 octane only) World Record: 573WHP / 537WTQ
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Old 09-03-2010, 09:31 AM   #5
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Got under the car and checked it..with the car's rear up on a ramp, handbrake on and 1st gear engaged, I grabbed the rear nut where the driveshaft connects to the diff and I could twist/rotate it about 1cm each way..is this normal? Should there be any play here? Also halfshafts have back and forth play of about 1cm (in/out of boots) but no rotational play here..
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N54 6MT TwinTurbo 1/4 Mile World Record: 11.43@126.6mph, 1.8 60', Stock 6MT 3.08 Gearing (Cayuga - Toronto Motorsports Park)
N54 6MT TwinTurbo 60-130mph World Record: 6.5sec 100-200km/hr, 7.5sec 60-130mph (vbox verified)
N54 (ACN 91 octane only) World Record: 573WHP / 537WTQ
N54 (96-98 Octane only no meth) World Record: 673WHP / 564WTQ
N54 (96-98 Octane plus meth) World Record: 693WHP / 572WTQ
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Old 09-03-2010, 07:30 PM   #6
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Along with UUC tranny mounts/bushings I've now put an order through for M3 rear subframe bushings, m3 rear control arms and diff carrier bushings...hopefully thump will be gone along with a lot firmer and stable/predictable rear end...
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N54 6MT TwinTurbo 1/4 Mile World Record: 11.43@126.6mph, 1.8 60', Stock 6MT 3.08 Gearing (Cayuga - Toronto Motorsports Park)
N54 6MT TwinTurbo 60-130mph World Record: 6.5sec 100-200km/hr, 7.5sec 60-130mph (vbox verified)
N54 (ACN 91 octane only) World Record: 573WHP / 537WTQ
N54 (96-98 Octane only no meth) World Record: 673WHP / 564WTQ
N54 (96-98 Octane plus meth) World Record: 693WHP / 572WTQ
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Old 09-05-2010, 10:50 AM   #7
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Here's a clip of driveshaft play. In neutral, handbrake on...notice how much the driveshaft moves and that the halfshafts also move as a result but much much less..think its this slack in the driveshaft banging around making the thump?

P.S. Excuse the Bon Jovi action on the radio

http://www.youtube.com/watch?v=49KHXjFXBZs
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N54 6MT TwinTurbo 1/4 Mile World Record: 11.43@126.6mph, 1.8 60', Stock 6MT 3.08 Gearing (Cayuga - Toronto Motorsports Park)
N54 6MT TwinTurbo 60-130mph World Record: 6.5sec 100-200km/hr, 7.5sec 60-130mph (vbox verified)
N54 (ACN 91 octane only) World Record: 573WHP / 537WTQ
N54 (96-98 Octane only no meth) World Record: 673WHP / 564WTQ
N54 (96-98 Octane plus meth) World Record: 693WHP / 572WTQ
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Old 09-05-2010, 12:12 PM   #8
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The halfshaft play looks normal, but there appears to be too much play on the driveshaft.... Have you checked play @ other end of driveshaft. The Guibo's that connect driveshaft to transmission are known failure points and could cause the amount of play you're getting. Can you get a buddy to listen for the clunk when you upshift?

Does your LSD allow you to remove end cap while installed so you can "see" the play and finally, have you contacted the mfg to ask them about the amount of play? What are the LSD's specifications in regards to tolerances (in particular play in the drive and half shafts?)....Could have a bad LSD...
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