2020 Alpina B7 driveline shudder during moderate acceleration

294 Views 5 Replies 3 Participants Last post by M_Bimmer, 11 d ago

patniven

Discussion Starter · 17 d ago

Just purchased a 2020 Alpina B7 with 19,000 miles on it. This is my 10th 7 series in 30 years and I've never experienced this issue before:
During moderate acceleration, the driveline shudders erratically as though the transmission or transfer case is "slipping" in and out of gear. I've even noticed it while gently accelerating and turning from a stop sign. During hard or full throttle acceleration, the car does not shudder. Local BMW dealer says he found no codes, and 87 octane in the tank (not sure how he determined the octane rating...). He suggests burning that out & fill with 93 (doing that today). I always use 93 when the car calls for it, but this car was delivered to me with a full tank. I highly doubt that low octane fuel is the culprit, but this is a B7, so the 4.4l engine is modified to produce 600hp.
Any ideas? Thanks!

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Robin750

· #2 · 17 d ago

patniven said:
Local BMW dealer says he found no codes, and 87 octane in the tank (not sure how he determined the octane rating...). He suggests burning that out & fill with 93 (doing that today).

There is a test procedure in ISTA to determine fuel quality.

I would also suggest checking the condition of the plugs, low mileage cars may not be warming up properly and that can cause carbon buildup. There is some truth to the Italian tune-up in these situations.

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M_Bimmer

· #3 · 12 d ago

Your 608HP N63B50 is hand built, and with 19,000 miles on it, it's barely broke in...I have +55K on my B7 (pre-LCI) and she is still pulling strong.

My recommendation is that someone take a close look at the driveshaft center mount, the transmission mount, the engine motor mount, and the differential mount. These are all rubber based items that will not throw a code, but if compromised, will create issues as you described.

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patniven

Discussion Starter · #4 · 12 d ago

Thanks for the responses. I found SIB 27 02 20 from May, 2020 (attached) that EXACTLY describes the issue I am having. Seems that there was an off-spec oil added to the xDrive transfer case during factory assembly. The fix is simply to replace the oil with the proper grade. Gonna take it to the dealer next week and have them perform this procedure.

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patniven

Discussion Starter · #5 · 11 d ago

M_Bimmer said:
Your 608HP N63B50 is hand built, and with 19,000 miles on it, it's barely broke in...I have +55K on my B7 (pre-LCI) and she is still pulling strong.

My recommendation is that someone take a close look at the driveshaft center mount, the transmission mount, the engine motor mount, and the differential mount. These are all rubber based items that will not throw a code, but if compromised, will create issues as you described.

View attachment 1085784

Thanks for the input. I've had "guibo" problems on previous LWB 7 series. Those were fairly easy to diagnose, as they created a thumping sound coming from the driveshaft tunnel during acceleration. The shuddering I'm experiencing is not heard, only felt during accelleration. Feels like the XMSN is shifting in and out of gear rapidly. Apparently, it's the clutches in the xDrive transfer case slipping...kinda like an old muscle car Posi-Traction rear differential with the wrong gear lube in it. Those old units needed "climbing gear lube" to allow the clutches to perform properly. Normal 90w gear lube did not work.

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M_Bimmer

· #6 · 11 d ago

Kind of hard to provide meaningful "help" via a forum....glad you got it sorted.

I plan to pull my turbos, when I get ready to do my 60K spark plug change, because they seem to be "rattling", and will inspect the gate flaps for "looseness". I have a few oil leaks to take care of too, but nothing too serious.

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2020 Alpina B7 driveline shudder during moderate acceleration

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