Diagnosing a front-end clunk upon acceleration

[prostcfc]

I've got a front-end clunk that generally only presents upon initial acceleration from a stop. It's a single clunk/creak. Sometimes I can feel it through the gas pedal. Car is on Ohlins R&T and has had end links replaced (Turner Adjustable) and FCABs with Turner Monoballs recently, by the PO; guibo as well. With that said, doesn't mean there aren't issues with any of the above installs. There are no vibrations and car drives fine on the track when accelerating hard and at speed. I've read that some have issues with NVH and ungreased Turner FCABs. Since I'm not hearing it from the rear at all, I feel it isn't diff/driveshaft related, and if it was the engine mounts, I'd get more vibrations/symptoms in general.

This winter I plan on doing some refreshing up front, but hoping to get this sorted as well. Any ideas on where to target is appreciated!

[prostcfc]

Bump.

Over the winter I completely overhauled the front:
- H&R Race camber plates
- MCS 1WNR w helpers
- OE front control arms
- OE inner and outer tie rods
- BW Trackcab FCABs > was previously using Turner monoballs and thought this may be the culprit, but swapping to Trackcabs didn’t change much
- BW end links

Clunk is still there, occasionally upon first acceleration, sometimes turning, and when I jerk my steering wheel left to right and vice versa there is a “clunk-clunk”.

What are some things I could be missing? Something in the steering rack? Motor mounts? I really don’t think it’s related to anything I changed given it hasn’t really changed behavior.

[liam821]

I would say tie rod ends, but you changed that. Have you checked the lower steering joint (#5 in this picture)?

[RockyMtnM3]

prostcfc I am experiencing almost the exact same thing. Does it sound like it comes from one side more than another? What I hear sounds like it comes from the driver side. I inspected and it looks like the Driver front sway bar bushing is shot and maybe the sway bar is knocking on the upper chassis, see attached.

If that does not fix it, I was going to start where liam821 suggested.

[prostcfc]

prostcfc I am experiencing almost the exact same thing. Does it sound like it comes from one side more than another? What I hear sounds like it comes from the driver side. I inspected and it looks like the Driver front sway bar bushing is shot and maybe the sway bar is knocking on the upper chassis, see attached.

If that does not fix it, I was going to start where liam821 suggested.

I didn't check the sway bar bushings when I had the belly pan off (though checked the torque on those 4 fasteners and they were fine, but should have checked the bushings for wear). I'll take a look.

What am I looking for in the steering joint? Just general play? I did check the torque on the steering rack to the front subframe and that was fine as well.

[RockyMtnM3]

Not saying it is the issue, but I would be curious how your bushings look. My plan is to replace the sway bar bushings first and assess.

What to look for in the steering joint? honestly, no idea. I need to learn more but at 135k general play is fair grounds for replacement to me.

I will give updates along the way if you don't get to a logical conclusion first.

[Black107]

This thread is so timely. Chalk me up as someone with the "single left front clunk upon acceleration from a stop" mystery noise. I first noticed it after having rod bearings, FCABs, motor mounts, and an alignment done last year, still on my stock suspension setup at stock ride height. At first I thought it was something the alignment shop did and they mentioned that sometimes when the original top hats get moved after a long time (he gave me as much camber as they'd permit) the bearing in the top can get cranky. I've since coilovers (MCS 1WNR), camber plates, end links, LCAs, and tie rods. The steering coupler was already done before all of this. Yet the noise remains. So the list of possible suspects seems pretty short now. I'm still running the original swaybar and swaybar bushings in the front, so that's my primary suspect at this point. Haven't had time to get under the car and take the tray off for a better look yet, any other ideas?

[liam821]

prostcfc I am experiencing almost the exact same thing. Does it sound like it comes from one side more than another? What I hear sounds like it comes from the driver side. I inspected and it looks like the Driver front sway bar bushing is shot and maybe the sway bar is knocking on the upper chassis, see attached.

If that does not fix it, I was going to start where liam821 suggested.

Good call with the swaybar. My old PY car had a similar clunk, which turned out to be the swaybar link. I would have sworn it was a loose coilover from the sound it made.

[oceansize]

Aftermarket sway bar links are the cause in a large percentage of these "clunk" issues. They come loose (even if you can't tell its loose) and waa-la. Anytime I get a clunk the first thing I'm doing is tightening the f$$$ out of those links.

[prostcfc]

Aftermarket sway bar links are the cause in a large percentage of these "clunk" issues. They come loose (even if you can't tell its loose) and waa-la. Anytime I get a clunk the first thing I'm doing is tightening the f$$$ out of those links.

I agree. Even though I went from Turner adjustable end links (on my old Ohlins) to BW adjustables (on my new 1WNR) and the clunk was on both, I think I'll disconnect the driver end link and see if that changes.

Interesting that Ground Control says this about their end links: "Please do not compare to other kits that ask you to use a 3/8 rod-end into the BMW 10mm hole, it just doesn't work. That is a loose fit that only gets worse, especially when driven hard." There is defiantly space in both the strut and the sway bar holes, so maybe it's shifting a bit on cornering, etc.

[liam821]

I agree. Even though I went from Turner adjustable end links (on my old Ohlins) to BW adjustables (on my new 1WNR) and the clunk was on both, I think I'll disconnect the driver end link and see if that changes.

Interesting that Ground Control says this about their end links: "Please do not compare to other kits that ask you to use a 3/8 rod-end into the BMW 10mm hole, it just doesn't work. That is a loose fit that only gets worse, especially when driven hard." There is defiantly space in both the strut and the sway bar holes, so maybe it's shifting a bit on cornering, etc.

I had a Ground Control bar on my previous M3, and the swaybar endlink had that exact problem; the bolt was too small in the rod-end link. I ended up 3d-printing a small spacer that fit around the bolt to fill the gap, which worked perfectly.