Help! BC coilover clunks

E

esafaeian

Member
Hi All,
I recently purchased and installed BC RS (BR) coilovers, the model with rubber top mounts for my z4 coupe 3.0si.

I’ve noticed when going over certain pot holes I’ll get a clunk noise, if it’s a dip in the road or general I ever surface then it’s fine. Only seems to happen when one side gets compressed due to a pot hole on that side that the car goes over.

I have checked all bolts and they’re fairly tight. I checked the top nuts and all were tight except the back right which I tightened up a fair bit. This unfortunately resulted in my allen key head snapping off inside the top nut allen shaft….. no idea how I’ll get it out, have tried digging it out with sharp blades, screwdrivers and a drill bit but I’m worried not I’m damaging the allen sides inside the shaft too much so have left it for now.

Anyway, suspension still makes a clunk over certain deeper pot holes. When I installed the coilovers the instructions said to have the rear heigh adjustment on the springs placed on the bottom, but there’s barely any space to adjust the spring height on the rears with the adjusted on the bottom so I installed it on the top (doubt this would cause an issues? Most installs I’ve seen have the adjuster on the top anyway). I set the ride heigh on the rears, then loaded the springs up a bit and then jacked them up more to about 8-10mm then I bolted the shock and adjusted it to match the hole in the control arm.

I’m not sure what I’ve done wrong or if I’ve done anything wrong (apart from snapping the Allen head inside the top nut shaft). I’m at a loss, I’m starting to think maybe clunks over deeper potholes are the norm for coilovers and I should just avoid them on the road as best I can.

Ps I’ve set the shocks to the softest setting.

Any help or ideas would be greatly appreciated!
 
I've heard on some types of coilovers that the actual coils can touch and make noise when then spring compresses.
 
These are the same design as the standard suspension no? Not coilovers as such (apart from fronts) so that should make no difference.

As above probably the front springs touching, you’ll see marks on the springs from where it happens. Get some rubber silencers to go on the touching coils, should sort it out.

If not maybe a ride height issue and your hitting the bump stops. Aftermarket suspension can and is likely to be noisier regardless due to extra stiffness so be aware of that in any case.
 
Hey, yeah I believe they're similar to standard suspension except obviously you can adjust the ride height and dampening.

The spring coils already have rubber strips on parts of them and the car isn't slammed so I doubt the coils are touching.

The clunk is only present over certain deeper potholes (was worse when I had the dampening adjusted at the midpoint between soft and hard).
 
esafaeian said:
The clunk is only present over certain deeper potholes
Click to expand...

Yes I have the RA version and spent ages trying to track down the cause but so far no joy . I set them up the same way as you . No problem on flat roads which are few and far between but is annoying on bumpy stretches of road . It was mentioned on a post by enuff_ Zed or bigwinn that it could be down to anti roll bar positioning but I havn`t got round to checking this yet .
 
It might be the actual hardware itself, within the actual strut. Not to sound condescending (truly because I was paranoid about these very issues when I was shopping for suspension) but you get what you pay for. BC coilovers are just one of the myriad of chinese no label coilover systems that are sold. They're blanks with another companie's label slapped on them. Trust me, as I had done extensive research on this for a while before buying coilovers. I wanted to save money, look good and perform better and without any headaches. That doesn't exist, you gotta pay to play with something that gets abused and is as volatile as a car suspension.

I came to this conclusion when I was shopping for suspension myself. I have friends that ran BC coilovers, Stance coilovers, Fortune Auto coilovers, etc etc. They all had issues within weeks/months, weird sounds, leaky suspensions, corroded rusting parts, etc. You do get outliers that get a miraculous set that gives them zero issues but that's not the norm.

You might have to get it rebuilt or use their warranty for the side that's giving you problems because it might be internally or it is defective.
 
my clubsport kw units can be abit clunky at times, ( solid mounts)... , back to the question i hope you get this sorted soon, i have driven lots of cars with coilovers and tbh they all seem to make some noise to a degree.
 
Anti roll bar bushes and drop links all good?

Oddly enough I'm chasing a similar noise under the same circumstances but on a stock X5(!) I've just done ARBs and a drop link on the noisy side and it's still there and I'm coming to the conclusion that it's a rattling brake pad. The noise clears off if a brake as I go thru a pothole or drain cover. And I've noticed I can make it on demand tapping the brakes lightly.
 
BC are a solid company that produce pretty good value dampers. I have experience with them in a couple of Z4s and in my 650i, and do rate them for fast road use.

Like you, I was very neurotic about the clunks, which only ever occurred over low speed crappy tarmac. I took all apart and spent ages playing wrong with spring pre-load, all while communicating via emails with with BC (who offered to inspect them if I sent them in). Dampers felt perfect, I had no play whatsoever in the top mounts or anywhere else in my suspension, so I could only conclude it's due to the solid mounts being much noisier (obviously) than rubber and that sound then travels to the bulkhead via the strut brace. I confirmed this by removing my brace and driving the car without it up and down the road - noise was significantly reduced.

I also broke an Allen key inside my front strut top nut. I just took it off and shook it upside down. At that point I was so proficient at doing suspension work on the Z4s that it only took me 15min max to do that.

Yes, rear sprint perch should be installed at the top so you can access. As you have figured, no issue will come from this. Set your damper length correctly though, that's important so you maximise your droop while keeping the spring loaded so it doesn't bounce.
 
I had the same issue when i installed my BC racing kit, however it was the anti roll bar drop link had snapped.
 
I put BC on my previous Si, with the bushed top mounts. Worst thing I ever done, they feedback so much road surface noise and bumps, fine for the track, not the road. So yeah they would "bang" over potholes. Didn't have the stomach to rip them out and replace, ended up selling the car, which was a mistake.
I'll never buy BC again, Koni sport adjustable appeals to me now.
 
If its only happening when one side compresses, then it's almost certainly going to. Be arb related, so I'd be checking droplinks.

You mention you have the type of bc coilovers with rubber topmounts - is that for the rear or both front and rear? If you have the spherical bearing fronts then they'll clonk away and that's entirely normal. Also worth noting that some dampers where they are solidly mounted to the car you will hear the valves snapping shut. It's normal but again another reason why most road cars don't go for dampers and utilise a lot of rubber mountings!
 
Hi mate, hope you've figured your issue out! However if you have not, you might try tightening the bolts on the strut braces up front. I used to have this same issue and it was because these bolts were loose, quite fortunate it was such an easy fix for me.
 
Hey guys, here’s an update - I took it to my BMW mechanic who checked over all bushings and the suspension, all was fine, he said it’s just down to the coilovers. BC then told me to take the car to Pedders as they’re a suspension specialist…. I took it there, they checked everything and the install, all was fine surprise surprise, so then went back to BC and after a lot of going back and forwards and then wanting me to do a ridiculous amount of s**t to diagnose the problem they ended up sending me two replacement inserts.

I haven’t replaced the inserts yet, Pedders told me the coilovers need to be set firmer on the car and that has made things quieter. I’m now just avoiding crazy potholes on the road and it hasn’t been too bad.
 
esafaeian said:
need to be set firmer on the car and that has made things quieter.
Click to expand...

What have you got them set to now as mine are set half way on the rear.
 
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