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Old Thu, Sep-14-2017, 04:53:42 PM   #27
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Default Re: Rumble in 2nd Gear Full Throttle/Heavy Load

Ujoint on the driveshaft or balance could still be the issue. Since the driveshaft is not solid in middle (it doesn't just bolt up front via guibo to tranny and in back via cv joint to diff with a solid metal cylinder in between) but has an extra ujoint in middle, it can create a standing wave with a certain natural frequency (engine speed/load/etc). I believe the rear cv joint is screw-on and I think you are supposed to mark it before disassembly so you tighten it to the same mark. A new one could have different balance than the original. Anything you change rotationally should be rechecked for balance, especially since it has to spin at x,000 rpm. Think of when/why you get your wheels rebalanced (even brand new/true wheels with different tire will probably be rebalanced slightly differently with different weight distribution of the rubber around rotational axis and then you get your steering wheel to shake at certain speeds, and then you might need to rebalance after some miles/tire wear). Just because the two parts might be balanced independently when put together they might not be since you introduce new degrees of freedom and boundary conditions.

Ujoint could be seizing from dirt/wear/scoring/age/etc. Could be a bit loose and too small of a difference for you to diagnose by moving 2 halves by hand (not enough torque applied).

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'85 528e 164k miles (sold)
'05 M3 6MT coupe

All DIY: 330 ZHP steering rack, diffsonline 4.1 diff with rem polish, E60 short shifter lever, AKG black diff bushings/subframe bushings, Rogue rtab, WPC rod bearings, Beyer driveshaft, full SS (SS stepped V1, catted S1, resonated S2, SS sport), Sachs clutch/flywheel, rear main, VANOS bullet proofing with anti-rattle, valve adjustment, cooling refresh, Ohlins R&T/Swift 448f 672r/GC street tops and camber plates, AFD E85 Proflex kit.
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