Suspension noise during autocrossing stresses

[3+5]

Sorry if this is an old topic, I tried searching and found nothing like this.

I've an 05 MZ3 hatch, 5sp. During hard driving, (namely autocrossing), there is the most horrendous clunk that comes from under the car during transitioning chassis loads. Accelerating, braking, engine braking, whenever the weight is abruptly shifted. Sounds like someone's banging on the floorboards with a ball bat. This is not a wheel hop, c/v joint or axle click, it's definitely from the suspension.

This happens with my stock hatch and a friend's 04, which is running 18" wheels, 2-1/2" lowered coil-overs & perf. struts and aftermarket sway bars (an MTX hatch as well). Anyone experienced this? Known fixes? I don't see any TSB's, and couldn't drive hard enough around the dealership neighborhood to duplicate it. Spectators & other competitors have reacted with "what the...?" It's loud enough to hear from a distance. It seems to require the tight confines of an autocross to occur. There, it happens all the time. It generally doesn't happen under normal road conditions. During VERY spirited driving at Deal's Gap in August, this clunk never occurred.

I'm an experienced autox'er & driver, ex USAF jet mechanic and sports car restorer. I can see no visible trace of this in the suspension or floorpan. It has me stumped, and I don't want to break something while racing. It's making me nuts.

I've written to Mazda and a few of the aftermarket suspension suppliers, all have stated they'd never seen this. I'd appreciate any help.

Thanks in advance.

 

[Solo2Protege]

as you say you're no noob to cars, all i can think of off the top of my head, is subframe shift? maybe the trans is shifting around....? but that sounds pretty extreme for such a new car...

I have never experienced any of those noises in my 04 sedan while autoxing.

Something has to be loose...have you dbl checked everything while weighted or unweighted? If weighted, try it with the car on jack stands.

Kinda one of those things where ya just have to either hear it or expereince it to get a better grasp on it.

 

[3+5]

Actually, that's good info for me to know you that don't get the same thing with your sedan. I'm gonna hunt this thing down, cause I love auto-x and hate this noise.

I read a post over on another board where someone eluded to the clunk being from failure of the sway bar bushings, but he hasn't responded to inquiries. I wondered of it were so, since my friend has poly bushings with the aftermarket bars and gets it too.

Nothing's loose underneath, I suppose it could easily be motor mounts or they sway bar itself thumping on the car as it twists or untwists... I can't duplicate it when the car isn't in motion, and it takes very hard cornering at that.

Thanks for the post!

 

[Solo2Protege]

ya, the sway bar endlinks may be something to look into...unhook them for an event and see if the noise is still there...but if your bud has upgraded endlinks and still has the same noise...

Is it a metal to metal sound? a grind clunk or just a thud clunk? does it happen once or does it happen multiple times in the same corner?

Does it sound like it's coming from the inside or outside when in the corner? If outside, it may be possible the strut and/or spring can't keep up and the spring slaps the perch as it re-seats itself...

 

[3+5]

That's a good idea, removing the bars would eliminate them. It's like a thud, or knock. As I said, like a ball bat, rather than a pipe or something mettalic. No grind. It happens once per "dynamic shift", like weight transfer caused by cornering and acceleration or deceleration. Only consistent when it reaches a certain point of stress on decel, like at the end of a straight where you really brake hard to the corner. Accelerating out of a corner, it only happens on the tightest of corners where you have to build speed. Not, for instance, in every turn of a slalom, but at the turn-in and possibly on exit. Sometimes it seems to be from the back, sometimes the front but always under the car. Very hard to tell exactly where.

I suppose it could also be springs seating. It seems to be on compression when accelerating, stretch on decel, but it's very hard to say. I though that such an obvious noise would be pretty common, especially since my car is new.

 

[ag bullet]

Sounds to me like the clunk that many of us have experienced at various times. You may need to look into a new rear motor mount from AWR (or is it AWP?). It is stiffer and is supposed to really help.

 

[BrianG]

I was getting this too and it was from the rear suspension in my case. The suspension bump stops may be hitting because they springs compress too far. Look for a smudged area where the bump stops meet the upper plate.

 

[tsunami]

from what your stating i would think more towards the spring unseating and reseating itself then the motor mounts... good luck with it andkeep us posted.