BMW xDrive is one of the latest AWD iterations to hit the mainstream, and it quickly became the standard for most of BMW’s road going models. Utilizing a wet clutch design, the electronically actuated BMW xDrive transfer case can send power to the front and rear axles independently, but naturally deliver a 40:60 front back split. Because the wet clutches are on the output shaft going forward to the front wheels, the only way the front wheels can get 100% of the torque is if both rear wheels are freely spinning. The front and rear differentials can vary between models, but in general both the front and rear differential in the BMW xDrive system are an open style. BMW’s with xDrive and DPC (Dynamic Performance Control) get the upper hand, with the addition of extra clutch packs in the differentials allowing the computer to individually control torque to each wheel, but for this blog that’s not important.
What IS important is making sure your BMW xDrive transfer case (the fundamental component in all of this) is in good shape, as it is NOT cheap to replace and is NOT available as separate parts. Luckily, that’s easy! All you need to do is change the fluid every 50-60k miles, and your AWD system should stay in good shape for years to come. If you don’t service your xDrive transfer case, however, plan on running into some major headaches down the road.
The most common failure is the worm gear inside the transfer case that get worn out, but as mentioned before, they are not available separately so if you let your xDrive get that bad, you’ll need to replace the whole thing. We prefer to do the simple maintenance and never worry.
Servicing your BMW xDrive Transfer Case
The transfer case is located at the end of the transmission, which is a little tricky to get to. In many situations, especially on 3-series cars, you will notice there is little to no space to move around. It will have a driveshaft going to the rear differential, as well as a driveshaft going to the front wheels. You can’t miss it. The situation will vary a little bit depending on if you have a car other than a BMW E90 (pictured below), as the X-series models like the X3 will have a slightly different design. To change the fluid, you will need a basic set of tools, with the inclusion of a 14mm allen socket for both the drain and fill plugs.
- Start by removing the large splash shield.
- Support the transfer case with a jack and a piece of wood, and remove the large aluminum mounting bracket that attaches to the body and the BMW xDrive transfer case mount. There will be six 13mm bolts holding this bracket to the body.
- Remove the two heat shield bolts right next to the bracket, you’ll need to move this around during the next step.
- Now remove the large bolt going through the transfer case mount. This is the trickiest part of the whole job, you have two options. The first (and proper) way is to drop the exhaust down and the bolt will slide out with no complaints. This is fine for those of you living in states without salty winters. For us here in New England, we will opt to leave those rusty exhaust mounting bolts in place and instead use the jack to manipulate the transfer case in situ and wiggle the bolt out. This will be a pain in the butt, as the exhaust pipe will block the rearward egress of the bolt. Be patient, the bearings and axles don’t like to be twisted. Gentle pry bar application of the bushing and the bracket can free up just enough space to knock the bolt out above the exhaust.
- With the transfer case still supported, remove the large bracket, which will expose the fill plug on the back of the BMW xDrive transfer case.
- Using the 14mm allen socket, remove the fill plug first. You do NOT want to remove the drain plug first, only to realize you can’t get the fill plug out. Then you have an unmovable car.
- Drain the fluid using the drain plug on the other side of the transfer case, it will be the lowest plug and be surrounded by cooling fins. Install the new drain plug to 44ft/lbs of torque.
- Using a fluid transfer pump, fill the Genuine BMW Transfer Case Fluid in until it overflows out of the fill plug hole. Install the fill plug to 44ft/lbs. We also have a much larger 1300cc transfer pump as well which is PN 7077.
- Assemble in reverse order, and hopefully that main mounting bolt won’t be too much of a headache. Getting it in is usually even more difficult than removal, so be prepared to spend some time here if you don’t remove the exhaust.
For the enthusiasts out there looking for a plain daily driver coupe or sedan with a 6-speed and a RWD setup, good luck. Most likely, you will find the BMW of your dreams will be equipped with xDrive whether you want it or not. If you are afraid of the extra maintenance that an xDrive car would require over the Rear Wheel Drive standard, don’t worry too much, as this service is only required once every 50k miles and will only take an hour or two for the seasoned DIY’er. From our experience, xDrive axles, bearings, and the rest associated extra hardware has not been a problem as these cars age.
But what about the Front and Rear Differentials?
While you have the car jacked up, and you’re already nice and dirty, you might as well change the differential fluids in the front and back as well. These are far more straight forward. The fluid will be a 75w90 gear oil, and we recommend the ROWE Synthetic TOPGEAR HC-LS 75w90, which is made to the BMW specification. This is good for all xDrive differentials, limited slip or non limited slip. It’s a good idea to get new fill plugs, as they have an integrated o-ring which tend to wear out.
The rear differential will have a single plug on the back in plain sight, the same 14mm allen style used for the transfer case. You will have to use the special tool to suck out as much of the old oil as possible. For a more complete service, remove the differential rear cover to allow the fluid to drain this way instead. This will give you the opportunity to wipe debris from the cover and bottom of the case with a lint free shop rag, but you will also need to add gasket sealant to your order. BMW specifies Loctite 5970 which is specifically formulated for high heat and chemical environments. Fill the new fluid in the same plug hole until it overflows, it should take around 1 liter. Done.
The front differential will have a plug on the bottom and a fill on the driver side (for US model cars). Crack open the fill plug and remove the drain plug. Install the drain plug to 44 ft/lbs of torque and use the fluid pump tool to fill the front differential with a little over half a liter of ROWE 75w90. It will overflow out of the fill plug. Install a new fill plug and torque to 44ft/lbs. All Done!
If you have any questions about this procedure on your car, just leave a comment below. Happy motoring, and remember, it’s called all wheel drive, not all wheel stop. If you are doing any serious winter duty, BMW xDrive is only half the equation. Invest in a set of Nokian winter tires and own the snow.