E39 Touring rear centre seatbelt stuck when seats down? Not any more!

[PZero]

Howdy folks, haven't been here for a while after the great forum crash, but thought my work today might be worth sharing. I've wrestled with this problem before but never been able to find an answer online, so here's mine. If I'm somehow crap at google and somehow missed a thousand other threads on the matter, meh, here's one more...

Meet the infamous / stupid ball bearing which has inconvenienced many an E39 touring owner. Anyone who has ever folded their touring rear seat down and found themselves unable to put it up again as the seat belt had locked in place without enough slack, has experienced the work of this little bastard.

After having that pleasure again today but this time removing the bench seat to unbolt the other end of the belt not being possible (don't ask), I had no option but to take off the seat back and get into the seat belt reel. Having now seen how this catch worked, I have no idea what it was trying to achieve other than pissing me off, so out it came. Et voila, belt once again works fine, inertia lock still works as it should (as that's a different unconnected mechanism, related to the only spring you see in the following images) and it doesn't get stuck in any position. Finally just like any other seatbelt.

Not saying that everyone should go and do this right away, in fact I would say don't unless / until you have to, as getting the seat back off resulted in four out of eight built in plastic clips on the carpeted seat back being broken (almost unavoidably as they are recessed in and away from the edges, so can't be levered out of their slots), and if you do do this, once you have unbolted the seatbelt assembly, make sure that you only remove the cover which runs the full length of the belt assembly and has the Bowden cable going into it, NOT the small round black on which is the size of the reel. Get the wrong one and the winding spring will burst out and either your belt is knackered or you have a fun hour or two trying to re-coil it perfectly.

I've read previously that this bearing catch was there to stop the centre belt reeling in too much when seat folded, but having seen the mechanism now I can't figure out how that would have been the case as it in fact stops the belt being pulled out, not in. The brown ratchet wheel in the pic turns with the reel, counter clockwise as belt pulled out. As can be seen, when this lock engages then the belt can reel in (clockwise) but not pull out (counter clockwise). 

The Bowden cable at the bottom of pic is slaved to the seat release handle, so as soon as you release the seat to fold it, the arm is pushed up and the lock is engaged, as shown here. The bearing rolls down and wedges underneath the arm, holding it in place and preventing counter clockwise turn of the reel.

When seat back lock mechanism is then closed again (manually or by folding seat back up again), the Bowden cable doesn't pull the block out of the ratchet wheel, just gets out of the way of that blocker arm. The ball bearing holds the arm in blocking position until seat back is upright again, when gravity rolls it back into a very shallow depression in the bottom bit which is in line with a matching cut-out on the underside of the arm. Arm can then drop, reel can then turn once again.
(Unfortunately I don't seem to have taken a pic of that, only of me holding the arm out of the way so I could pull out some slack. Just imagine that my thumb isn't there.).

The bearing operated catch is a separate assembly, and can be just slid upwards out of its mounting on the seat belt assembly.

 

Having now gotten the this bearing catch out and examined it, it's apparent that if it's only a few degrees off level on either left/right or front/back axis then the bearing rolls out of the centre and pushes the very lightweight and loose arm upwards. This would explain why I've never been able to free my belt by patient jiggling for 5 minutes until I get lucky, as seems to work for some. I live on a steep hill, and my driveway is sloped so my car is never level at home, hence that bearing and gravity conspired to always hold the blocker arm in place.

Cons? None that I can see. Everything works as it should, no locking when it shouldn't, and inertia locking works as usual so no worries at MOT time. I can't see why BMW put this in there in the first place. But if any issues do become apparent, the bearing bit can just slot right back in again. 

May be of use to someone!

Edited June 2 by PZero