04 June 2016

Single Stage versus Dual Stage Airbags

The early coupes have single stage airbags.  The later ones have dual stage.  The steering wheels are identical between the 2 airbag types, but the airbags are different (obviously) and also the slip ring cassette that houses the airbag and horn wiring.  I had previously written about the excellent new steering wheel I bought from Dimitri Maar on ebay (search for use "Tainik").  The wheel Dimitri sent me was from a single stage car, and the coupenut project car has a single stage airbag.  So, no problem.  It was a straight swap.

I bought a second wheel from Dimitri for my S54 since I was so happy with the first one.  In this case, I sent Dimitri a piece of Walnut OEM BMW leather and he made the wheel with it to match the BMW Black/Walnut wheel.  Again, Dimitri used a wheel from a car with a single stage airbag.  When I got the wheel, I removed the wheel from my S54 coupe, transferred the slip ring from my wheel over to the "new" Tainik wheel, and put the car back together.

There was a clicking sound when the wheel turned.  No good.  Turns out, in addition to the slip ring, the clip that unlocks the slip ring and allows it to uncoil is different too.  The clip is mounted to the wheel at about the 7 o'clock position.  It is compressed by the 16 mm bolt that secures the wheel to the steering column.  See photos.  The dual stage clip is slightly smaller and a different shape than the single stage.  And, mine was painted yellow.  You need to use a dial stage clip and a dual stage slip ring with a dual stage airbag.  The clip is not available separate from BMW.  It may be possible to modify one to work one way or another, but luckily I didn't have to.

Also, I got a little confused about the wire routing from the steering wheel to the dual stage airbag.  I had to phone Andy and have him send me pictures of his factory, un-disturbed routing.  I am posting those for reference too.

Clip for dual stage airbag and slip ring is on the left, in yellow.  Single stage is on the right.

1 comment:

  1. I've been swapping a few steering wheels around lately, unfortunately, none have been for any of my own cars, but I have encountered that little clip. It appears to me, that its only purpose in life is to secure the slip ring from being turned, or at a minimum, being turned too far, while the wheel is removed from the column.
    As you discovered, and documented, it is "compressed" or made to pivot, unlocking the slipring, once the column bolt is replaced.
    If left with no other choice, and as long as you understood its purpose and function, a little time with a file would eliminate any interference.

    On another note, I'll have to remember to only wear CLEAN Latex gloves when I need to touch a walnut leather covered wheel... ;))