Hi all, It seems there is something came loose inside the steering wheel. How could I open the cover and take a look inside. Do I need to disarm the air bag first? Thanks.

(You should say what kind of car you have, your profile shows a 89 300CE)
On the back of the steering wheel there is a hole on each side (you can feel with your fingers). In the bottom of those holes are the heads of screws which release the airbag, I believe they are Torx T30, you'd need a real long Torx bit to reach the screw heads(about 2" long). If you have adjustable steering you should bring the wheel all the way out towards the driver to get better access to the holes. Once the screws are released they will stay in the steering wheel, which makes it easier to reinstall the airbag. Once the screws are released and the airbag is off, there is one electrical connector to completely remove the airbag. DON'T turn the key to ON after you remove the connector or you'll set a SRS light (fault because it dosn't "see" the airbag connection). Very very slim chance of anything happening in regards to the airbag exploding, I wouldn't worry about that at all. If you are SUPER nervous, then just disconnect the negative battery terminal before working on it (extend the steering wheel adjustment out first).
Gilly

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Hello Gilly, thanks for your advice. The problem is I cannot find the right Torx socket. I get the part #126589001000. I called few places and went to Auto Zone, they did not carry it. I checked with the dealers, they told me to wait at least two weeks. Where can I get it sooner?

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89 300 CE

No airbag on my car, so can't help with removal. I did, however, discover a strange rattling noise whenever I turned the steering wheel one day. Sounded almost like a glass rolling on its side, which was most disconcerting. Prised the horn pad off - took quite a tug to dislodge the rubber lugs holding the centre star - and found it was one of the horn cage mounting bolts rattling around inside. You'll understand what I mean if you take a look. Checked all the screws and bolts while I was there and found most of them were loose. Can't think why, maybe vibration over the years?

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1987 300e manual 250,000 km (sold)

For the tool try "samstag sales" on the internet, they sell lots of new MB tools, I'm sure they have it.
Gilly

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IIRC, I used a like sized allen wrench. Just be careful not to strip anything.

glenmore
1991 300CE
1990 LS400