[Greyfox]

Originally Posted by Kunlune90

changed transfer case fluid today for E90 2010 328i xdrive, 126687 miles. First time transfer case fluid change.

Let car sleep before drain the transfer case fluid. Put in OEM transfer case fluid.
Drained out about 350 mL fluid and put in about 500 mL. The fluid drained out is black but no burnt smell. The same smell as the new fluid. Maybe the long miles consumed some transfer case fluid, but there is no code and the car drives normal.

Driven 15 miles with no codes. Scanned with OBDII and no hidden codes. Seems setting not needed.

There is a fluid condition sensor in the transfer case just like in the automatic transmission. It took me using a Schwaben scanner for BMW to reset that sensor.

[Mark963]

I'd seen the FCP Euro video and read threads about removing the transfer case bracket to do the transfer case fluid change. Living in the rust belt, I avoid touching the rusted exhaust components at all cost. Then I stumbled on this thread. At the last oil change, I took a closer look and felt the fill plug by reaching both ways around the bracket and it didn't seem that bad.

I bought a 14mm hex socket off ebay for too much and used a washer and ball joint extracator to press the hey key out of it. Later I read that some 3/8" coupling nuts have an outside dimension that's close enough to 14mm to work as the hex key and they're about a dollar. Most say the outside fits a 9/16" wrench which would be 14.29mm. As long as it fits the plug is all that matters. I thought that length might be somewhat important, but I think longer is just fine.

I happen to have a Gear Wrench 14mm ratcheting wrench which is the PERFECT tool. I tried to use a friend's much nicer wrench and it could probably do the job but the head around the ratcheting part was slightly bigger in diameter and it wouldn't clear the bracket next to the drain plug.

A little tape around the middle of the hex bit so the wrench slides over it, but there's some friction, might be helpful.

After doing this on mine and finding about as easy as the front diff, I loaned the tools to a friend for his. This is an easy job and I can't imagine playing around with removing the bracket.

The process I followed, as I remember now:
1) Clean the area around both fill and drain plugs and above the mounting bracket. Brush/rub it clean and spray with a bit of brake cleaner.
2) Hold the ratchet in your left had (I'm right handed) so it will loosen the fill plug and push the end up through the gap between the TC bracket and the TC and in front of the fill plug. Then take the hex bit in finger tips of the other hand and take it over the bracket, put it into the wrench and push the bit into the plug.
3) Loosen the fill plug. If it's too tight, hook a closed-end wrench on the 14mm wrench to extend it and if that doesn't work, wack the end with something heavy. Then turn it about 1 turn using the ratchet. Then you can either use just your finger tips on the perimeter of the plug or use just the hex bit in your fingers to turn it the rest of the way.
4) Get your catch pan in place and loosen/remove the drain plug. It's much more exposed but a standard 14mm hex socket won't work there either without removing some other stuff. The hex bit in the Gear Wrench wrench is perfect.
5) After the fluid drains, reinstall the drain plug.
6) Use any sort of pump and route the hose over the transfer case bracket into the fill port. Don't get any loose debris into the port. SHAKE THE FLUID. Pump it into the TC. I used a jar and aquarium pump with a hose attached.
7) Either with finger tips or with the fill plug on the hex bit, start it into the fill plug. Then use the wrench.
8) Use your favorite tool to reset the TC fluid.

Thanks to the OP and everyone with the great advise here.

[Virtual Factoid]

Thanks Mark963 for the detailed write-up. I did this today pretty much exactly the way you did it except for one minor difference: I used a hacksaw (with a blade for cutting metals) and a vice to cut the hex key a bit shorter so that when it was fully inserted into the slot the part projecting out was just enough to have the wrench over it i.e flush with the back side of the wrench. With this arrangement I had just enough room to get the wrench with the hex key pre-inserted in it up the confined space. Made the job a tiny bit easier.

I found step #7 the hardest to do. It took a lot of fiddling with both hands (right hand over the bracket left hand up from under for support) to get the initial thread going.

Some advice to those who are considering doing it this way i.e. without removing the bracket, lowering the TC and the extra hassle involved with that: if you have short, stubby/fat fingers, don't do this. You'll probably not be able to use both hands with one over the bracket coming up from the top and the other through the bottom. Having thin long fingers would be the best but it is doable with average sized hands as well. You will need to use both hands at some point, there is no way around it.

This job looks impossible to do at the outset. Have patience and repeat to yourself: "others have done it, so can I". :-)

[Jloobee]

Thanks a Ton to all that contributed to this topic, I was about to either remover the exhaust or drop the TC bracket, neither of which I wanted to do. So after reading this I went into the garage (car was already jacked up on stands) and started looking for the fill plug, I did not see it and almost gave up until I spotted it. Then I started messing around with a 14mm allen and 14 M combo wrench, it looked impossible for a while, then I got my body in the correct postition (head towards drivers seat and feet towards front of passenger tire, in that position I could get my right hand above the TC bracket and wiggle the allen into position while on the box end. The plug was tight and I had to extend the wrench with another wrench and finally got it. The drain was easy, as was the refill, and getting the fill plug back in took some work but I got it in a couple minutes. Again, THANKS to ALL that provide input to this thread, you saved my tons of work.

[augustus maximus]

I made a mistake and put Redline 75W90 in my 330XI transfercase when I changed out the electric motor and was too lazy to drain it back out. That was 8 years ago and still running strong.