Enter our protagonist: a 2021 BMW X5 G05 xDrive45e with an owner who had just about enough of feeling like he was driving over a field of potholes every time he pressed the accelerator. "It jerks! It shudders! It’s undrivable!" he said. And, of course, it is a known problem.

Actually, no. It’s not a problem if you ask me. It’s something we’ve known about for over a decade.

The Not-So-Mysterious Cause

Here’s what happens. The xDrive system relies on a transfer case that decides how much power goes to the front and rear wheels. 40% front, 60% rear in normal conditions. But when traction changes, the system adapts, shifting power where it's needed. Brilliant! Until it isn’t.

Over time, the clutch pack inside the transfer case wears, and the transfer case oil loses its friction modifiers. When that happens, the system gets confused. It thinks the wheels are slipping when they aren’t, so it constantly shifts power between the axles. The result? Jerking, shuddering, and a very grumpy owner.

Right. Off to work.

Step One: Disable xDrive

First, I needed to confirm the issue was with the xDrive system. You can do this in a few ways—pull the fuse, unplug the transfer case, or disable it in ISTA. I chose the latter. Test drive? Smooth as silk. So, yes. xDrive was guilty.

Step Two: Blame the Tires (But Not So Fast!)

BMW says there can be no more than a 1% difference in circumference between the front and rear axles. But here’s the thing: this isn’t an exact science.

I grabbed my tape measure and checked the customer’s 21-inch winter tires (genuine BMW, star-marked, just a few months old). Difference? 1%. Right on the limit. Suspicious.

So, I swapped on the customer's summer wheels. Test drive? No more jerking.

The logical conclusion? The tires were the problem.

But wait! I’ve seen this before. A good transfer case with fresh oil isn’t this sensitive. The real problem is usually hiding elsewhere.

Step Three: Throw Oil at the Problem

Next, I changed the transfer case oil. No drain plug? No problem. Out comes the vacuum pump. Oil out, new oil in. The owner was sent off to drive 200 km and report back.

500 km later… no change.

Fine. Let’s try again. Another oil change, this time free of charge. Another 500 km later? Still jerking like a caffeine addict.

At this point, logic dictated that the transfer case needed replacing. I’ve done it before, and it always worked.

Step Four: Stubbornness Pays Off

But then, the customer—who at this point was fully invested in the experiment—said, "Let’s try changing the oil one more time."

Now, I’m not one to argue when someone is enthusiastic about spending less money, so we went for it. But this time, I did it properly.

  1. Removed the entire transfer case from the car.
  2. Opened the fill plug.
  3. Turned it upside down.
  4. Let it drain for hours.

Back in, fresh oil. This time, 0.3 liters extra.

Test drive? Smooth. From the first meter.

So, What Do We Learn From This?

You tell me. Because according to BMW, this should not have worked. And yet, here we are.

Moral of the story? If your xDrive starts shuddering, don’t just throw a new transfer case at it. Change the oil—properly. And if that doesn’t work, change it again. And again. And then, when you’re about to give up? Drain it upside down.

No, what do you say about that?

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