i found this on bimmer fest
DRIVER’S Seat Belt Replacement DIY
The Driver's and Passenger's FRONT Seat Belts are slow to retract. See this thread:
I decided to tackle this project (replacing the driver's seat belt) and did a write-up. The bottom line is that: The Brand New Drive's Seat Belt makes little difference, still slow to retract. The Spring inside the tensioner is not strong enough to retract the seat belt faster. It came from factory like this. LIVE WITH IT!
But if you decide to change the driver's seat belt, then here is the DIY:
Approx. $126 at dealer. Do NOT use aftermarket part.
* Raise Driver Seat UP and FORWARD as much as possible, so the bolt (Torx 50) holding the seat belt is accessible.
* Disconnect battery ground cable. Why? I forgot to do this, and spent 2h playing with the seat belt, taking pics, when done, the battery is dead from door lights being on. The battery was probably weak to start with, so I ended up with a new battery!!!
Figure 1: Loosen the Driver Side REAR Door Plastic Sill, held by at least 2 clips.
Figure 2: Using Flat Screw Driver, Pry the BOTTOM of LOWER Trim (held by 3 clips). Slide the LOWER Trim DOWN from UPPER Trim, then pull it out.
Figure 3: Remove UPPER Trim by prying the 2 plastic clips, then pull the trim DOWN and OUT. When re-installing, do NOT forget to pass the belt buckle through the UPPER Trim opening.
Figure 4: Most of the friction is caused by the seat belt rubbing against the Plastic Anchor. Nothing you can do about it. The bottom line is that the seat belt tensioner comes from factory with weak spring, so it takes a long time to retract the belt.
(In contrast, my 1998 Volvo V70 seat belt works great from day one, the spring is stronger and pulls the seat belt back nicely when getting out of the car).
Figure 5: The Seat Belt Tensioner is held by a single 17-mm Bolt. When re-installing, make sure the small tab on the new Seat Belt goes in the same hole.
Figure 6: Remove the middle bar (8-mm screws), and the 17-mm Nut holding the UPPER Anchor.
Figure 7-8: This is optional. You may bypass this step. But I did it so pic is included for completeness: The Plastic Cover on the side of the Driver's Seat: held by plastic clip and Torx 30 bolt. But when trying to remove it, I broke the little plastic tab in the middle (Fig 8). Then I found out I did not need to do this as the seat belt passes right through the slit in the Plastic Cover on the side of the Driver's Seat.
Figure 9: The END of the Seat Belt is anchored by a Torx 50 bolt (at the bottom of the Driver's Seat Track). Remove this bolt, and pull the seat belt up through the slit.
Figure 10: Anatomy of a Seat Belt, when you open it, the Spring came out like a Pandora Box, impossible to put it back in. So do NOT try to service or adjust the seat belt, if your seat belt is bad, get a new one from dealer.
So….The morale of my story is that:
1. If you seat belt works fine and slow to retract, LIVE WITH IT! Getting a new seat belt will NOT solve the problem.
2. If you decide to change the seat belt, then disconnect the battery, otherwise, you may end up with a new battery like me.....
3. Teach yourself a new habit: when getting out the car, unbuckle your seat belt, hold the seat belt metal buckle with your LEFT hand, get out of the car, then throw the seat belt metal buckle on your seat to prevent the door banging against it and the door sill (damaging paint work), the seat belt will eventually retract, but it will take up to 30 seconds or 60 seconds.
4. Anyway, I am back to square one, the seat belt still slow to retract......but I have new seat belt and new battery.......Oh and a write-up for you guys.....