Clunking on hard cornering from front suspension

[Open Loop]

First, I searched and could not find anything definitive regarding this issue:

2013 FRS 30,000 miles, set up for D Street as follows: Koni Yellows, Strano front sway bar, RPF1 with Bridgestone RE71R's, crash bolts.

On my 5th and 6th runs at an autocross yesterday, I had clunking on hard cornering (and the clunk seemed to occur when turning very hard left and right). I thought it might be the clamps that retain the Strano front sway bar from sliding side-to-side, but I tightened those and the bar looks centered to me and had no effect.

Clunking seems to be best replicated by turning hard right (about 50% as hard as a hard autocross turn), and by entering a driveway ramp (uphill) at an angle turning right, so that the front right goes up first, and then when the front left wheel goes up, I get a clunk. I.e., in both instances, when the left suspension is compressed and/or when the force is pulling the left wheel away from the car i get a clunk.

Clunk feels like its at my feet and is relatively loud/very noticeable, but does not seem to upset the car very much.

Thanks for your thoughts in advance.

[Gforce]

You have checked for the obvious, a front wheel lug nut not properly torqued? Heat cycling of the wheel/hub and brake disc can loosen a lug nut randomly and fairly commonly.

A long shot would be the steering rack moving in its bushings?

Otherwise, could be a failing shock, they tend to clunk when the internal valving starts failing. Check for oil seeping out of the left strut. They can fail without leaking. I've had konis fail internally, no leaks which I thought was due to a PO bottoming the rear suspension on a car lowered too much. I don't know that but too short springs can result in shock running out of stroke. Front struts are very robust though so this is unlikely.

LCA bushings sometimes fail but not usually at low mileage or age.

Roll bar drop links are another common source of clunks if they fail.

I assume you have jacked up each front wheel to full droop and checked the front springs are fully seated correctly. Check the bump stops are still intact.

[Open Loop]

Originally Posted by Gforce

You have checked for the obvious, a front wheel lug nut not properly torqued? Heat cycling of the wheel/hub and brake disc can loosen a lug nut randomly and fairly commonly.

A long shot would be the steering rack moving in its bushings?

Otherwise, could be a failing shock, they tend to clunk when the internal valving starts failing. Check for oil seeping out of the left strut. They can fail without leaking. I've had konis fail internally, no leaks which I thought was due to a PO bottoming the rear suspension on a car lowered too much. I don't know that but too short springs can result in shock running out of stroke. Front struts are very robust though so this is unlikely.

LCA bushings sometimes fail but not usually at low mileage or age.

Roll bar drop links are another common source of clunks if they fail.

I assume you have jacked up each front wheel to full droop and checked the front springs are fully seated correctly. Check the bump stops are still intact.

Thank you for your thoughts. Not loose lug nuts. I doubt it's a blown shock as these are set at half turn from full soft, in the car for only three thousand miles and were not making any weird noise two days ago. Not leaking. Stock springs seated correctly, bump stops intact, and sway bar end links are good and tight.

I've checked the top strut bolts, the three top strut mounting bolts on each side, and the strut braces and all are okay. Lower strut bolts okay. Sound seems to be coming from lower than that.

I have experience with loose wheels, bad end links, binding upper strut bearings on other cars and this clunk is not like those sounds. It sounds like a loose rear control arm bolt on a miata but on the front, and those bolts are tight. It doesn't have the feel of lca bushings going bad and I can't imagine they are the problem - too new and not abused enough.

Are the steering rack bolts that come loose the two main bolts that connect the rack to the subframe?

Thank you. I am going to pick the car up for the third time today to hunt around.

[mav1178]

Or bad front hub bearing.

[Open Loop]

Originally Posted by mav1178

Or bad front hub bearing.

Thank you. My experience with bad hub bearings is a droning noise, not a clunk. And if was at the point of clunking, the wheel would be wobbling. Wheel is very tight and both bearings sound good when I spin them by hand with the wheels on. I think the clunk must be coming from something else.

[mav1178]

Or bad front upper mounts.
We can go down the list but there's only so many things that are mounted on the front of the car between suspension and chassis.

[Open Loop]

Originally Posted by mav1178

Or bad front upper mounts.
We can go down the list but there's only so many things that are mounted on the front of the car between suspension and chassis.

I saw a thread suggesting this. I've had bad upper strut mounts on other cars, but typically that has a sensation of binding up the spring, and it letting loose causing a sound. This feels different but if I cannot get the sound to go away by taking out the sway bar I will likely turn to replacing the upper strut mounts. Thanks again.

[mav1178]

Originally Posted by Open Loop

I saw a thread suggesting this. I've had bad upper strut mounts on other cars, but typically that has a sensation of binding up the spring, and it letting loose causing a sound. This feels different but if I cannot get the sound to go away by taking out the sway bar I will likely turn to replacing the upper strut mounts. Thanks again.

That's not the sound.

A loose or bad upper strut mount is like bad coilovers or if your shock nut was not tightened properly. It feels like someone taking a hammer and tapping your front shock as it moves up and down.

A bad stock mount can be easily seen from the engine bay, the rubber will look like it's cracked or deformed.

A bad aftermarket pillowball upper mount requires disassembly to inspect properly.

[ls1ac]

Back to the simple, the crash bolts could be shifting. Put a paint mark along the side of the suspension piece. Hard cornering will shift the mount but bolt will still seem tight, retorque it.

[Open Loop]

Originally Posted by mav1178

That's not the sound.

A loose or bad upper strut mount is like bad coilovers or if your shock nut was not tightened properly. It feels like someone taking a hammer and tapping your front shock as it moves up and down.

A bad stock mount can be easily seen from the engine bay, the rubber will look like it's cracked or deformed.

A bad aftermarket pillowball upper mount requires disassembly to inspect properly.

Yes, this does not describe the sound I am hearing and my stock upper strut mounts looked fine and felt fine a few months ago when I put the Konis in. Mine is a once-at-a-time clunk when compressing the left front suspension that feels like it's coming from a control arm or fsb. Thank you.

[redlined600]

Have you checked for the endlinks or sway bar hitting the control arms?

[strat61caster]

90% of my suspension noises on this car have been end link related, and getting that lower nut can be a PITA, the other thing I can think of is the sway bar mount plate thingy.

[Open Loop]

Originally Posted by mav1178

That's not the sound.

A loose or bad upper strut mount is like bad coilovers or if your shock nut was not tightened properly. It feels like someone taking a hammer and tapping your front shock as it moves up and down.

A bad stock mount can be easily seen from the engine bay, the rubber will look like it's cracked or deformed.

A bad aftermarket pillowball upper mount requires disassembly to inspect properly.

Originally Posted by ls1ac

Back to the simple, the crash bolts could be shifting. Put a paint mark along the side of the suspension piece. Hard cornering will shift the mount but bolt will still seem tight, retorque it.

Originally Posted by redlined600

Have you checked for the endlinks or sway bar hitting the control arms?

Originally Posted by strat61caster

90% of my suspension noises on this car have been end link related, and getting that lower nut can be a PITA, the other thing I can think of is the sway bar mount plate thingy.

Crash bolts remain tightened to 120 lbs and no sign of shifting. Fsb supports are tight. End links were not hitting control arms 3 days ago and i double checked the clamps that keep the fsb from sliding back and forth.
Sound is best described as a "knock" and occurrs at about 20% of max autocross force. My plan after driving in to work today is to double check the nuts on the top/center of the struts, and if that doesn't work, take out the end links or end link/fsb assembly entirely and see if that fixes it. Thanks again for your input.

[strat61caster]

In my experience top nut knocking occurs without any steering input, you can hear it over a bumpy road.

Best of luck.