Clanking sound underneath

[Champ]

Hi all. I'm new to the forum, having owned my '06 NC now for just about 2 months. I really like the car for all the usual reasons but there's just one problem. When I hit a sharp bump/depression or pot-hole on the road, a very distinct clank/clang? sound can be heard underneath the car. I'm nearly certain that it's from the rear end and it can be from either side. You'd imagine that it would be easy to identify the source but that's not the case. I've spent hours underneath swinging out of every possible part that might be loose but I've found none. 2 motor mechanics to date have drawn a blank on it. (Not Mazda mechanics but good nevertheless). There are no damaged bushes or loose suspension links. The exhaust isn't loose and it doesn't touch anything. The anti-roll bar and drop links are fine. The brake calipers, pads and hand-brake links are good. I've hit bumps with the handbrake on and I still get the clank; ditto with brake pedal applied to tighten up everything in that department. Cross braces are tight. Anyone out there come across anything like this before? Maybe it doesn't happen to Mk1s or 2s. I'm really puzzled at this stage (and a little bit fed up). She's got 42k Km and hasn't had a rough life. She drives and handles well .. feels nice and tight. It's a mystery.

[mx5ash]

Are you sure it's not something in the boot? Jack/jack handle etc? Sorry to ask if you have checked but a friend was once told by mechanic that his front shocks needed replacing but that didn't solve he odd knocking. Turned out to be the bonnet hinges were slightly bent out of shape and were causing the noise
Ash

[Champ]

Forgot to mention that I'd emptied the boot too but the noise was still there. Thanks for the response, Ash.

[mx5ash]

It's always hard to diagnose a noise from a car, even harder over the Internet! Just thinking aloud here,
Loose wheel nuts
Loose alloy centre caps
Loose nut on shock mounts or shock rod.

[landmarkjohn]

I would still be looking at suspension components. One of the cleverest things I saw on a forum is "bushings are like brakes, they wear out". I have just spent €1000 replacing worn suspension on my Xedos 9..... getting there but still need rear shocks. Our '98 MX5 with 150k km is so tight in comparison I am amazed.

I would try driving over speed ramps slowly to create the noise, one back wheel at a time if you can find a suitable ramp, if you can consistently create the noise and like you say there is nothing else obvious then some part of suspension is favourite in my book. Keep us posted and good luck:-)

[Champ]

Thanks all for sound advice. Pardon the pun.
Will take it all on board, keep at it, and advise.
Just wondering .. any suggestions on where in Dublin I might locate a good mechanic who knows his way around MX5s ?

[Champ]

Well it looks like I've managed to locate the source of the noise. It's taken a very long time. Even though I was convinced that the shock absorbers were in good condition - no sign of any unusual seepage, etc, I had another close look at them. This time I noticed that the white plastic cups which sit down on top of the shock bodies could be slid up and down by hand. It seems to me now that it is essential that they fit tightly down as far as they can go onto the top of the shock absorber body. If not, you get what I described in my original post. They had clearly, over time, slid themselves up a bit. So far, all that I have done is to apply a layer of insulating tape to the top rims of the absorbers and then to force the cups down tightly over them. They are now a very tight fit and there is definitely no gap between the top of the absorber body and the lid of the cup. Maybe I'll give them a lick of epoxy just to be sure.
I am amazed that this could have produced the sound as it did. The cup and shock, as they were, sounded like an empty pot being hit with a hammer any time they took a sharp knock. Now all is nice and quiet. At last .... Let's hope things stay this way.
C
http://s297.photobucket.com/albums/mm223/conorcampion/MX5/