Help me track down a noise - Saab C900 content

The last few times I've driven the Saab I've heard a clicking noise that occurs when the direction of the force on the axles is reversed. So for example, after pulling out of a parking spot in reverse, upon starting forward there will be a single click. This seems to happen after hard braking as well, i.e., coming to an abrupt stop, then starting off again. Never more than one click, nor under any other circumstances. It feels like slack is being taken up somewhere.

It seems to me this is most likely something related to the axles, but I can't find anything wrong. I inspected and serviced all four CV joints when I had the car apart over the winter, and it's been fine for months since then. I also replaced the tripod bearings on both sides, and the inner driver on the right side. The left side got a new wheel bearing; the nut was replaced and properly torqued. The only play I can find seems to be in the transmission/diff. Grabbing a wheel and turning it in gear gives me one inch of rotation measured at the surface of the tread, which seems reasonable, but my experience with FWD in general and Saab transmissions in particular is pretty low.

I suppose it's possible something else is shifting back and forth, but I don't know what. The exhaust is firmly attached as far as I can tell; the muffler hangers are new. The front motor mount was replaced and is secure, and the others seem intact if a bit soft. The control arm mounting points are good (right side professionally repaired some years ago, left side original and solid). All front sway bar bushings have been replaced.

Any thoughts as to what to check, or how to better check the axles, is appreciated.

The lack of response makes me think perhaps I've scared off all but the Saab people. For those unfamiliar, let me clarify the setup. The engine is longitudinally mounted, with the combined trans and diff below. The halfshafts extend directly out from the diff just like they would in a transverse-mounted FWD setup with a transaxle. The suspension is a conventional double wishbone arrangement. I found this diagram - oddly enough, it was found in an eight year old thread on this very forum.

Hopefully that makes it a little clearer.

In reply to 02Pilot :

Can you feel anything when it clicks?

No idea, but check the lower control arms, which are known to fatigue and fail. Commonly, they break during a reverse maneuver while turning. The break occurs close to where the angled part of the arm is welded to the round portion that pivots in the bushings. If you look at the diagram you linked to above, the "lower wishbone" call-out is pointing to the piece I'm referring to, in case I'm doing a crappy job of describing it. 

If this is the problem, you can either weld it or, if still available, replace. I had one fail years ago and the Korean-made aftermarket arms had decent welds, good finish. 

In reply to Pete Gossett :

No, so far it's just a noise.

In reply to procainestart :

That's interesting. I can't say it's more pronounced in the conditions you describe, but it is definitely evident. I'll have to have a look at the control arms and see if I can find any signs of cracking. At ~$50 a piece, it seems a no-brainer to just replace them both if that turns out to be the problem. Thanks for the info.

Haven't had a chance to get under the car yet, but doing some reading on the lower control arm cracking - which is disconcertingly common, apparently - makes it pretty clear to me that I should just replace them for peace of mind. I've already got new bushings sitting on the shelf, so two new arms and I'll feel a lot better about not dying a fiery death. Hopefully that will also solve my clicking issue, but I'll know better when I get in there.

In reply to 02Pilot :

Fingers crossed. Nice that you can fire one round from the parts cannon without feeling like you're wasting time or money given the history of the control arms.

Have you had a good look for what things might touch what other things if those soft-ish engine/trans mounts are softer than they're supposed to be?

In reply to Ransom :

Yeah, finding there's a known problem with potentially catastrophic consequences that's also a possible (likely?) source for the noise makes this seem like money well-spent regardless. Having the parts be readily and cheaply available is just a bonus. They're on their way, so maybe by next weekend I'll have them in.

I really don't think the motor mounts are the problem here. The front one seems to wear out and cause problems, but I've already replaced it. The side mounts are positioned in such a way that even if they were totally failed I don't think the engine could move a whole lot, and there's nothing I can see in a cursory inspection that would be an obvious source of a noise like the one I'm chasing.