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      04-09-2021, 09:20 AM   #1
MetalsMan
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NEED HELP from Those with Lots of Suspension Knowledge

Good Morning,
I'm at my wits end with and issue regarding my rear suspension set up. Late last year, I installed MCS One, single adjustable dampers in the rear, hyperco springs with Ground Control Articulating Spring Upper perches. The dampers are mounted into the body with the solid clevis mounts. I have the dampers oriented with the damper shaft pointed at the ground so the adjustment knob is easily accessed.

So, that's the setup. I have not gotten it aligned yet, as I was waiting to swap wheels and tires first - just did that two weeks ago with a new set of 18's downsized from 19 stockers.

I never removed, replaced or adjusted the rear sway bar end links either.

The problem, very noticeable (think someone in the trunk with a hammer beating the inside of the car's sheet metal) clunking over sharp bumps like minor road imperfections or small potholes, rough surfaces. No noise over gradual dips/swells in the road, just sharp impacts.

If it helps, the noise isn't nearly as prevalent after install or reinstall - it seems to have increased after some driving until it's gotten very noticable

I laid the seats down yesterday and had my son sit back there while I drove over some rough surfaces in our neighborhood, trying to isolate the noise to a particular area and we agreed it's coming from where the damper is mounted to the body, like the solid clevice mount is bouncing up and down into the body. Maybe something is in a bind and cannot move quickly enough over sharp impacts

I have installed, removed everything and reinstalled the entire setup, torquing everything down properly and for the life of me cannot figure this out. When installing and reinstalling, the car is on a max jack lift, so no weight on the suspension.

Must be something I am overlooking or some suspension basics I'm unaware of.

Any help is much appreciated as I just want to enjoy the car. Please ask whatever questions or request any pics and I will be happy to oblige.

Thanks in Advance.
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      04-09-2021, 09:32 AM   #2
rborane
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I just had the same setup installed. MCS 1WNR - Eibach 600/900 rates, and ground control articulating perches. Also have the rear dampers with the adjustment knob on the bottom.

Did you cut the ground control perches at all? What spring rates are you running?

Asking about cutting the GC perches adjustment rod because there is limited clearance in the cavity which it sits in, and could be hitting against the shell itself, depending on how low the car is adjusted
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      04-09-2021, 10:11 AM   #3
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I'm running 1000lb rear springs. Yes, I did cut the threaded rod in the ground control perches - Don't believe there should be any of the threaded rod sticking out of the piece that is inserted into the body. I guess it could be possible, but I don't think so. Will definitely consider this as a possible cause. I remember it being pretty difficult to estimate how much to cut off to get the desired stance but also leaving enough within the mount to not affect the structural integrity
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      04-09-2021, 11:22 AM   #4
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I have adjusted the rear height using those articulating perches, not by much, but I guess the side making the most noise could possibly be due to that. I'd have to remove to be sure but I feel like it is something else. Everything else is tightened to spec though and I don't see where there is any rubbing that would cause the same noise on dips/swells in the road when the suspension compresses
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      04-09-2021, 03:10 PM   #5
rborane
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What length rear springs do you have?
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      04-09-2021, 03:19 PM   #6
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I'm surprised you don't have any bump stops on the damper. Have you measured whether it's possible for the damper to bottom out?

I run 1000lbs/in rear springs on my F31 and still get into the bump stops.
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      04-09-2021, 03:41 PM   #7
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The springs are 8", I didn't use any bump stops because I installed them the way they came directly from MCS. I didn't want to try to disassemble to install the bump stops. Guess I could cut some that I have and wrap the shaft though.
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      04-09-2021, 03:50 PM   #8
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Quote:
Originally Posted by FaRKle! View Post
I'm surprised you don't have any bump stops on the damper. Have you measured whether it's possible for the damper to bottom out?

I run 1000lbs/in rear springs on my F31 and still get into the bump stops.
Quote:
Originally Posted by MetalsMan View Post
The springs are 8", I didn't use any bump stops because I installed them the way they came directly from MCS. I didn't want to try to disassemble to install the bump stops. Guess I could cut some that I have and wrap the shaft though.
MCS don't require bump stops. Spoke directly with them and they are designed to not require. You have the right spring length, and rate is good as well. I honestly don't know what it could be. I'll pay attention to my setup since it is identical to yours (I run a 8"- 900lb rear spring), but haven't noticed any noise that you have described
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      04-09-2021, 04:17 PM   #9
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Thanks - agree - no idea what it could be. Most likely something simple. Hoping someone chimes in with a "well have you thought about this?" and I can share and aha! moment
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      04-09-2021, 05:03 PM   #10
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I'm no expert here, but any chance you could mount a Gopro in there and get a birds eye view of what's going on in motion when the noise is occurring?

Also, maybe a Chassis Ear could be of benefit in getting you in the ballpark, though I've never used one personally

https://www.amazon.com/STEELMAN-0660...8005698&sr=8-3
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      04-09-2021, 05:03 PM   #11
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Check to see if the bolt securing the shock to the lower control arm is torqued down.
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      04-09-2021, 08:13 PM   #12
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Quote:
Originally Posted by jfritz27 View Post
I'm no expert here, but any chance you could mount a Gopro in there and get a birds eye view of what's going on in motion when the noise is occurring?

Also, maybe a Chassis Ear could be of benefit in getting you in the ballpark, though I've never used one personally

https://www.amazon.com/STEELMAN-0660...8005698&sr=8-3

Yep, that's a great idea. Maybe I can get my gopro strapped under there
somewhere and get some video. I'll try that in the morning. I have thought
of the chassis ears as well. I don't have any, but probably worth the
investment for now and into the future.

Will report back.

Yep, the lower strut bolt is torqued correctly. I haven't double checked,
but the last time I reinstalled the setup, it was torqued down to the right spec.
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      04-09-2021, 09:46 PM   #13
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Quote:
Originally Posted by rborane View Post
MCS don't require bump stops. Spoke directly with them and they are designed to not require. You have the right spring length, and rate is good as well. I honestly don't know what it could be. I'll pay attention to my setup since it is identical to yours (I run a 8"- 900lb rear spring), but haven't noticed any noise that you have described
Funny, because I called MCS and asked this exact question a few weeks ago and their answer was, "We just supply dampers to our vendors and whether they pair bump stops with the kit they sell is up to them." Furthermore they said there aren't any internal bump stops like some people on these forums believe.

Now it's true you can make a setup that doesn't compress enough to engage a bump stop, but a 1000lbs/in spring at the stock location isn't high enough for that in my experience for all normal driving cases.

Last edited by FaRKle!; 04-09-2021 at 10:02 PM..
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      04-09-2021, 10:07 PM   #14
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Quote:
Originally Posted by MetalsMan View Post
Yep, that's a great idea. Maybe I can get my gopro strapped under there
somewhere and get some video. I'll try that in the morning. I have thought
of the chassis ears as well. I don't have any, but probably worth the
investment for now and into the future.

Will report back.

Yep, the lower strut bolt is torqued correctly. I haven't double checked,
but the last time I reinstalled the setup, it was torqued down to the right spec.
You can also check to see if there's any play/looseness with the monoballs at either end of the damper. You'd have to take the damper out of the car to inspect this.
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      04-10-2021, 09:33 AM   #15
MetalsMan
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Quote:
Originally Posted by FaRKle! View Post
You can also check to see if there's any play/looseness with the monoballs at either end of the damper. You'd have to take the damper out of the car to inspect this.
Yep, checked those out along with the bushings when I reinstalled
and there wasn't anything out of spec.
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      04-11-2021, 01:29 PM   #16
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For the fans of this thread,. I'll be getting up under the car this afternoon finally to take a look. Going from stock struts, to a custom JRZ/MCS/KW type damper requires using bushings at the bottom and top mounting locations to take up the on either side of the monoballs.. I wonder if there is some.l play becoming present between the bushings/spacers and the lower control arm
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      04-15-2021, 10:04 AM   #17
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Any update here?
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      04-19-2021, 08:58 AM   #18
MetalsMan
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So, re-torqued the lower damper bolt, and the control arm camber bolt. No change. I removed the rear trunk floor, and the battery panel that houses tools for tire change, drove around - no change. I put my son in the car again last night with some tape to place tape where he heard the noise - see pic. I can't figure it out. I finally have some time this evening to work further on it. Maybe something behind the trunk liner? Maybe I need to remove the damper on that side completely and run around the block with just the spring back there and see if that does anything.
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      04-19-2021, 09:40 AM   #19
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Searching the forums, see some people have had knocking issues in the rear due to improperly torqued rear subframe bolts. I may need to check those. Also, improperly routed emergency brake cables though I had already had the dealership take care of that.
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      04-19-2021, 09:20 PM   #20
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See there was a recall for rear subframe bolts on some cars. Wonder if this could be it. I found the recall notice. Says that if there is ever a repair to the rear subframe, if it is removed etc for any reason, it is necessary to replace the subframe bolts and not reuse them. The torque setting is different as well. I will check into this tomorrow
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      04-21-2021, 01:50 PM   #21
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Last thought. I have removed and reinstalled the lower strut bolt as well as the lower control arm to wheel carrier bolt next to it several times. I heard some of these bolts may require replacement. I wonder if one has stretched a bit and is causing the knocking noise
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      04-30-2021, 03:21 PM   #22
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Ordered new rear subframe bolts, installed and torqued to new recommended 108NM. No change. Still getting the knocking noise.
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