As advertised, I deployed my airbag, and quite by accident (On jackstands). Unfortunately, the greenbooks on the SRS system are not actually as great as most of the rest of the greenbooks are. Let me explain the circumstances under which it went off...

My steering has been stiff when I start, but generally is fine by the time it warms up. I've worked on this in other threads. Long story short, the I concluded that the rack was the problem and obtained a ZF rack out of a junkyard to fix it. (on my 1991 240, it had a CAM)

So, I switched 'em. I also replaced the tie-rod ends, as they were on their way out. Relatively straight-forward--unbolt the two u-bolts, undo the tir-rod ends, and you mostly there. You also have to undo the lower U-joint, and mine was simply not coming. After PB blaster had no effect, and beating on it with hammers (usually with wood between the hammer and the surface) was equally fruitless, out came the torch.

Well, the torch worked well, and freed up things, off it came with a little more encouragement from my hammers.

Note: all the while I was trying to keep my steering wheel straight. This was simply because I wanted the signals to cancel properly. Anyway, to get a good angle on things, I would occasionally turn the wheel 90 Degrees. Then I'd turn it back, and re-fasten it with my bungee.

Anyway, then I reversed the process. Got the lower u-joint to mate with the steering shaft, got out the rubber mallet to encourage everything to go together nicely. Then, two bolts on the driver's side, u-bolt on passenger side, then the tie-rod ends.

Easy-peasy. Then I added fluid, & started the car (still on jackstands, w/o tires on it yet). I was turning the wheel stop to stop to bleed the system, and it was going well. Then I turned the wheel to the other stop, and heard a crunching noise from the steering wheel. I was concerned... but not real sure what to do about it. My thought was, "crap, my signals probably will not cancel properly." So I went back and fourth perhaps 6 more times, verifying the fluid was good. Then I came back from one stop, and BANG! There went the airbag. Fortunately, I was standing out side the car, and reaching in through the open window... My right hand is a bit sore, but that's it.

Anyway, as I never opened up the steering wheel or did any electrical work... I just don't understand how this happend. Like I said, the SRS books say that you should always reset the steering wheel when working on the rack or the steering shaft, but never really went into why.

So... Has this happened to anyone else? And does anyone know why?

As a side note, my power steering works great now. And I'll probably look into getting a non-SRS steering wheel for replacement.

 

Was the battery disconnected when this happened?
You can get a bag from a junk yard, cheap.

 

battery was not disconnected. I didn't disconnect the battery as I wasn't working on the electrical system--all mechanical stuff, so I figured no big deal. I suppose I was wrong there. At any rate, the airbag went off after I had started the car again and was bleeding the PS system... Perhaps disconnecting the battery during the work would have made a difference?

 

Well, rereading your post, you were just turning the wheel, bleeding the air out of the steering rack when the bag deployed! Hm, I wonder if there is may be a short somewhere to cause the bag to fire--I don't think it should happen under the conditions presented. The electrical glitches in these cars are getting to be interesting...

 

I got the airbag unit out of the wheel. I had to go buy a T-30 screwdriver... I used interchangeable bits or ones that would fit on a ratchet... however... this needs a pretty long shaft... so, I got the T-30 screwdriver. Oh well... I kind of wanted a Torx set anyway...





So, here we have the air bag out. That wire looks crummy. In greater detail:




These wires were mangled. What we have here is a... what do they call it?... ah, "contact reel" failure. My horn is also out. Here is the inside of my steering wheel:


Looking at the horn circuit.... the Horn circuit is always live, then interrupted through the switch in the wheel, then grounds, I think, through the steering column. They don't show any wires leading back down to ground anywhere, and my examination doesn't reveal any... but I'll look more carefully when I take apart the system to replace the contact reel.

My working hypothesis:
Some how, the contact reel failed--it can only be turned a limited number of times in either direction. Perhaps somehow in my work I instigated this. Whatever the case is, the wires got twisted up, and as they don't look torn, I'm guessing they came out of their crimps. From there, they somehow came in contact with the live portion of the horn circuit--i'm guessing they use a contact ring for the horn or some other exposed contact, as the greenbooks are a bit vague here. Once they came in contact with the horn circuit, the bag deployed.

This is just my working theory. But it sounds about right to me. I still don't understand how I managed to mess up the contact reel... but here is the warning from the greenbooks: "Never unto steering shaft or steering gear without first locking contact reel and removing steering wheel." I failed to do this, and this has been the consequence. I still don't understand why... but when I get a new contact reel and can be out of a car long enough to more fully take apart the system, I'll post my findings here.

 

Well, I took things apart a bit more. I took lots of pictures... because I like threads with pictures.



This steering wheel works different than some other's i've seen. Most old Volvo 240s have their horns off to the side. The old '89 740 I had had the horns off to the side. But in the 1991, the airbag is mounted on those shiny metal brackets on the side. The screw comes up through the center of those, and latches into the airbag module. When you press on any part of the airbag, it depresses those shiny metal parts to close a contact and make the horn go. The screws for this type of 240 are trapped in the assembly--they don't come out. Anyway, I probably mentioned earlier that my horn doesn't work. My assumption was that something was wrong with the contact ring on the clock spring.


The big 'ole nut there in the middle is a 27mm. I had to get a socket for this. Deep socket works best... although depending on the design of your socket, you may be able to get away with using a normal socket. I didn't have a 27mm at all, so I got this.


Easiest way to get off is with an impact wrench. That way you don't end up turning the wheel much. K-jet.org wisely advised leaving the nut threaded a little bit so when you pull off the wheel, you don't jerk it into your face. I followed this advice--it seemed wise to me.


And now we are down to the clock spring and contact ring. You may or may not be able to tell, but there are some tabs that are supposed to be on the contact reel/clock spring that are missing. The broken off remnants are around 1 o'clock and 7 o'clock. You can also see around 10 o'clock where the wires were jerked out of if. Interestingly enough, there was no debris in this area (although a couple of stink bugs) leading me to believe that someone may have been in there before and possibly used a clock spring with those tabs broken off. I know the car had been in an accident, but I've never found out if definitively if the airbag went off or had been replaced. And maybe they just worked their way out... but at any rate, the contact reel/clock spring needs to be replaced.

Also, I tested to see if there was a problem with the contact reel that runs the horn. I touched a wire to the contact reel and grounded it to the steering shaft. And guess what? Horn worked just fine. So, my problem is in the wheel, not the contact reel.

So, now to get to the contact reel. It's not that hard, as long as you've got a trusty T-25....


Two screws on the top....


Two more on the bottom....

And one on either side that I forgot to take pictures of. The one on the right is a little difficult, because you have to take off a piece of plastic trim around the key area to get to it. Becareful as it breaks easily. In fact... I broke mine...

That will bring you to here:

(Note: I took these pictures when I put things back together, hence the reason the clock spring is out). Remove the two switches for the wipers and signals...

... and that will let you access the screws on the side...

... One...

... and two.

Then you can pull the whole metal assembly out, and when you do that, there will be three obvious screws on the backside to remove the clock spring. In theory, you probably could get to it without all of that... but it would be difficult. After removing the screws, you get to remove the bright orange plug that goes with the airbag, and the horn plug for the contact ring.


So, here is the clock spring/contact ring assembly. The red arrows point to where the wires ripped out. The blue arrow points to where you can see the inside of the clock spring is broken.

So, I found a decent deal on ebay for an airbag, wheel and clock spring, so I'm going to replace it that way, and then clear the codes on the SRS system. I will carefully follow the instructions in the SRS supplement in the greenbooks so that I don't have to go through this again. And next time I do work on the rack... I'll be taking apart the steering wheel to prevent this from happening again.