Would loose rear strut top bolt make knocking/rattle noise?
 

Hello,

I installed BC Racing coilovers on my car and I noticed today that I hear a knocking or rattling sort of noise from the rear when I am driving on anything but a perfectly smooth surface. Any bumps and I hear it. At first I thought it might be the spare tire bouncing or something but it's bolted tight.

When I installed the rear coilovers and I put the tophat on them to install into the car, I did not torque the strut rod nut down very hard. The tophats are torqued to the body of the car though. Could that be causing the noise? Everything else is torqued down on the suspension.

To be clear I am talking about the bolt where you have to hold an allen wrench in the center of the strut rod and turn the nut around it to get it tight.

When I reach under the wheel well and push and pull on the strut rod, on one side there is a little play in it. The other side is tight. Please let me know if this could cause noise, or if you can think of anything else to check. It almost sounds like a box is shaking around against another box making a knocking sound, it is not high pitched like a marble rolling around in the trunk or something.

Thank you

BC coil-overs seem to be famous for the rear set knocking. Don't know the answer but I'll bet some solutions have been posted.

That said, tighten the bolt.

Dang. It is driving me frickin crazy. I pulled the spare tire and everything out of the trunk to make sure it wasn't that. I will see if anyone else answers and I'll tighten the nuts tomorrow. If that doesn't work I'll try calling BC next week.

The car drives like a dream though - it handles so well I love driving it every day.

That top nut not being tightened properly can definitely cause noise...i know it has for me in the past on OEM style replacement dampers

as Slarti mentioned the BC's have been widely known to have a rear clunking sound, there used to be a ton of posts on this...the only thing is I'm not sure if its still an issue or something that was corrected a while ago cause your post is the only one I remember in years where people complained about it...but yeah, definitely start with tightening the nut

I can't think of what part of the strut would make that noise, so I am hoping the problem was my dumbo installation. I'll fix the top nut and double check all the bolts back there.

It does do it on bumps so I guess there is a possibility something inside the damper or body could be knocking when the strut compresses or rebounds. I did have to turn the front right damper 5 clicks harder than then left to get it to stop bottoming out, so I am not very confident in the build quality and consistency of the struts.

I would probably opt for $1500 coilovers next time to be honest.

I thinks it s a pretty common installation issue for me I've done it on both front and rear dampers, the fronts are easy to correct because you can just pop the hood and stick a wrench on the bolt...the rears the only way I have found to do it properly was putting it in a bench top vise and its only a matter of like 1/2-1 turn on the nut if that and the sound went away

Ok every buddy, I have an update. First of all, the noise was coming from the rear right.

I took the wheels off because I was going to pull the struts out and torque the top nut and I noticed a build up of what I think was tire powder on the retaining ring on the right coilover. Then I turned the ring and it was loose. I couldn't see any place that the tire was rubbing on, and no rub marks on the tire, so I am not sure what that was all about. Maybe it was just tire dust that built up during my driving at 1 inch toe out before I got my alignment done.

Anyway, I set the strut length to match the left side and tightened the retaining ring very tight so it won't move again.

It was getting dark so I put the car down and went for a drive, and the sound is 100% gone! Woohoo! The loose ring had worked its way up which would in effect increase the preload. I am not sure if that caused the knock/rattle, or the loose ring caused it to rattle. I am not sure what was rattling, but it's gone now.

Thanks for the suggestions. I still need to pull the struts out and tighten the top nuts properly one of these days...

glad it got fixed suspensions noises can drive a person nuts, I wouldn't even bother pulling the damper if theres no noise its probably fine, enjoy the new coils!

Update!!!

Ok, the knocking noise came back. Maybe it never went away and I just didn't realize it. I came to learn my "type" of knocking was common. It would only happen at low speeds on say, a gravelly road or road with little cracks in it, Knock knock knock rattle rattle from the rear right.

I emailed BC and they told me check the top nut and preload. I pulled the right strut and what do you know, the top nut was loose and the top hat made that juddering sound when I moved it around. I used the impact gun to tighten it, checked the left side, and now it really is gone. Perfectly quiet. It was the top nut this whole time.

After my first test drive I checked the preload and found that it was about 1cm too much. Not sure how I did that, but I fixed that too, now the car feels smoother from the back, the shocks actually absorb impact instead of going BOOM on every little bump.