[OilDripper]

The front diff in my 2011 X3 started to make noises on deceleration. Sounded like a bad wheel bearing. It was very, very loud. Took it to my usual BMW guy - fantastic small shop that I have used since the car came off warranty. He said it would cost about $1,500 in labor plus the cost of a used diff (he estimated $300-500).

Given the car has 190,000 miles on it, I wasn’t thrilled about putting $2k into it. That said, I do love the car and have done a variety of things to extend its life over the last three years (OFHG, valve cover, new brakes, new rear shocks and springs, new front suspension). I have done most of that myself and thought I would give replacing the front diff a go.

I spent a fair amount of time on the Interweb looking at the forums and YouTube and couldn’t find detailed step by step instructions. I found one half decent video where the guy replaced a front diff on an X1. I figured it couldn’t be that different (no pun intended) so off we went. Given that I couldn’t find anything specific to an X3, I thought I would memorialize the steps required for the benefit of others who may find themselves in a similar position.

The first step was to get a replacement front diff. A new front diff is something like $3k. I managed to find a used one out of a wrecked 2016 X3 for $200. That car had 40k miles on it so I felt confident the diff would be fine. It was even near me so I could pick it up and skip the cost of shipping. I confirmed the part number for my existing front diff and the superseding part numbers to make sure the one I was buying was the correct one with the 3.38 ratio. Depending on the condition of the diff you buy, you may want to replace the axle seals on it prior to installing it. The one I bought looked good so even though I had bought seals I skipped that and will be returning them. You do need to buy the two bolts that secure the knuckle/hub to the axle. My understanding is those are one time use bolts.

Once you have your parts here are the steps. Note that this is the cheater (or shortcut) method. The proper method (and the one my mechanic was going to use is to remove the engine cradle/subframe).

- Remove the belly pan.
- Remove the skid plate by removing the four bolts attaching it to the engine cradle.
- Remove front wheels.
- While you have a friend push down on the brake, remove the axle bolts from the hub center on both sides. If you don’t have someone to help, you can loosen the bolts by removing the center caps on your wheels for access before you lift the vehicle and remove the wheels.
- On the driver’s side undo the sway bar end link from the knuckle side, undo the headlight leveling arm from the front control arm and remove the bolt on the back side of the knuckle that clamps down on the strut. Remove your brake line and ABS sensor lines from the clips to give them some slack.
- You should be able to drop the knuckle/hub assembly from the strut and have enough room to get the outside end of the axle out from behind the knuckle/hub. You will need to support the knuckle/hub with bungees or a rope or chain after the axle is out so as not to the strain your brake line.
- You can now remove the driver side axle by using a striking a chisel or pry bar on the back side lip of the axle where it meets the differential. It won’t take much force. A gentle tap should get the axle moving so you can pull it out completely.
- Repeat the same procedure on the passenger side of the car.
- Remove the air box,
- Remove the charge pipe from the air intake (very carefully - but if you have high mileage car expect it to break). Gently maneuver the charge pipe towards the front of the vehicle.
- You should know have a clear view of the single bolt on the stud that is holding the engine mount bracket to the engine mount. On the passenger side you shouldn’t need to move or remove anything; you should be able to clearly see the nut. Remove both nuts.
- Under the car detach the driveshaft from the differential and move the drive shaft aside out of your way.
- Remove the four bolts holding the differential in. The bottom two are super easy. The top two? Not so easy….expect to swear a lot. You won’t be able to fully remove the top rear bolt until all the other three are out and you can move the differential around in order to get clearance to remove that bolt. The three other bolts are the same length and fairly short. The top rear bolt is long and can’t come out with the differential in its installed position.
- Now that you have all the bolts out you need a friend, a jack and a large pry bar.
- Get the jack under the engine; place some wood on the jack so you aren’t jacking directly onto the pan. I put some two by fours on the top of the jack so that I spanned the oil pan. Jack up the engine - it doesn’t need to come up much; maybe an inch or so. Just enough so that the engine mount brackets clear the studs on the top of the engine mounts.
- Now you can have your friend get under the vehicle with you and use the pry bar to move the engine to the passenger side. Again, it doesn’t need to move much. Maybe an inch or less. This will create enough clearance for the differential to drop out. Put a folded up moving blanket on the floor before you do this, or be prepared to catch the differential when it drops.
- Drink a beer to celebrate successful front diff removal.
- Remove the breather tube from the differential. It uses the standard BMW squeeze and pull clip. Install the breather tube on your new used differential in the same orientation.
- Important: If you don’t want to repeat the third prior step and the one below, put the long bolt into the top rear mounting hole BEFORE you continue to the next step. Ask us how we know…..
- Get your friend to use the pry bar again to move the engine while you finagle the new used differential into place.
- Replace the four bolts. We found that just starting the three shorts bolts and then starting and tightening down the long bolt fully sucked the differential nicely into place. YMMV. Tighten up the remaining bolts.
- Carefully and very slowly lower the engine back onto the studs. Have your friend under the vehicle to watch to see if the studs are lining up with the bolt holes. They may need to use the pry bar to finagle the engine into position.
- Replace the two bolts on the engine mounts.
- Reattach the driveshaft.
- Reinstall the axles.
- Slide the knuckles back onto the bottom of the struts and reinstall the bolt securing the bottom strut into the knuckles. Note there is a tiny protrusion on the back side of each shock. That protrusion needs to line up with the slit on the back of the knuckle, or else the shock won’t drop down into place.
- Reattach the sway bar end links (and the headlight leveling arm on the driver’s side). Put your brake lines and ABS sensor lines back in their clips.
- Install new hub bolts to secure the knuckle/hub to the axles. You will need your friend to press on the brakes in order to tighten these down to the recommended torque specs.
- Reinstall the wheels.
- Reinstall the skid plate and belly pans.
- Reinstall charge pipe and air box.
- Test drive your car!

It took the two of us probably eight hours to do this. That did include fully removing and replacing the intake manifold as I wanted to change the gaskets (trying to chase down a lean code), and stumbling through figuring out the whole engine mount thing. Hopefully with these steps you could get this done in four or five hours.

Now to replace that charge pipe……

[Subydayo]

Any pictures?

Could you describe the sound it was making when slowing down?