GetBMWParts
BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read

Go Back   BMW M3 and BMW M4 Forum > BMW F80 M3 / F82 M4 Technical Topics > Suspension | Brakes | Chassis

Post Reply
 
Thread Tools Search this Thread
      07-24-2019, 07:49 PM   #1
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Racer20's deep dive into the strut clunk.

Final Edit: Here's what fixed it. Spoiler alert: it's the steering gear. You can skip most of the gobbledegook below unless you want to fall down the same rabbit hole I did trying fruitlessly to solve this issue.

-----------Original Post--------------

There are a bunch of threads on this issue already, but I've started down my own rabbit hole of figuring out what's going on myself rather than relying on hearsay and paid-by-the-job dealerships to solve the issue.



The problem:

A loud metal-on-metal clunk that sounds like something heavy is loose in the suspension. Isolated to the drivers side on my car.

Vibration felt through the floor and pedals, noise sounds like it's coming from the strut tower. No vibration through steering wheel.

In addition to the noise, it seems that there's more harshness being transmitted through the drivers side suspension, but this could also just be the road surface.

Occurence:

Driving at low speeds over sharp, upward-protruding road imperfections, causing the suspension to compress quickly. I have a test bump near me in an empty parking lot that creates the noise consistently. Reversing over my test bump turns it into a sharp rebound drop rather than a compression hit, and the noise is not present in reverse.

Driver's side only: Hitting the test bump with the passenger side wheel at the same angle and speed does not produce noise.

Occurs in all suspension modes, including when the damper is unplugged (locked in full stiff). Noise severity gets worse with increasing damper stiffness.

Noise occurs regardless of steering input or brakes on/off.

This problem seems to occur mostly on cars that have had suspension work done and mostly on the driver's side, but I haven't verified this thoroughly at all. Chime in if your experience is different.

Other people complain about clicks, creaks, and noises while steering. These noises might be related, but I don't have any of those issues. Mine is specifically a heavy clunk over sharp impacts, more prevalent at lower speeds.

My car:

2015 M3 19" wheels, EDC, (June 2014 production)
CS suspension swap (= ZCP dampers and rear sway bar)
MP HAS
CS EDC/GHAS/MDM/EPS Coding
(Ride height set to BMW recommendation and alignment set to factory nominal settings)

The basics:

My initial suspension installation was done by me*, with all new hardware and proper torques.

*Except the ZCP rear sway bar. The shop that did this work also found that my drivers side front lower control arm was bad, so they replaced it. I didn't ask any questions or get the parts back at the time because there was no noise or other problem. The noise started occurring gradually about 1000 miles after all this work, earlier this summer (I did the suspension retrofit last summer/fall and when I put the car away for the winter, everything was fine.)

Here are the first few things I checked, and didn't find a smoking gun:
  1. Everything feels and looks tight and in good shape. I can't find the noise by hitting anything with a mallet. I've looked at everything under load with the car on ramps and with the suspension at full droop with the car on jack stands.

  2. My sway bar end links are not preloaded at curb position. (Some people claim that correcting a preloaded bar fixed their issue, at least temporarily, but this isn't verified and it did nothing for me.)

  3. I've dyno tested the drivers side damper and found it to perform exactly like when I put it on last year. No degradation whatsoever. I can feel a clear difference in ride when switching modes; there's no indication that the EDC system is malfunctioning. Edit: This is not true, see post #21 for update.

  4. There has been some discussion in other threads about adjusting a bolt on the steering gear to take up slack and eliminate play. (Some people claim this fixed their issue, at least temporarily)

    Don't. My friend who works for Bosch in steering gear development said not to touch that bolt, that there's a specific procedure for setting the preload and doing it yourself could cause heavy wear and screw things up. Take it to the dealer if you think the steering gear is an issue.

Prime candidates/interesting findings:

The upper strut mount:

(Some people claim that replacing this fixed their issue, at least temporarily, but this isn't verified)
  1. My upper strut bearing (plastic thing between the spring and top plate) had a lot of play. I replaced it (just the plastic piece) with a tighter one from a ZCP with just 6k miles on it. The road texture isolation improved on that side of the car and the steering effort reduced in right turns, but the clunk is still there.

  2. The washer in the upper strut mount that the strut rod sits against and clamps to has some witness marks and fretting damage, and I can feel the edge of the witness mark with my fingernail, indicating that the washer material has been compressed.

  3. BMW changed the upper strut mounts from 3 bolt to 5 bolt attachments in late 2014. I can't think of any good reason to make this change except to solve a joint stiffness issue.

    My suspicion is that the noise is caused by the upper mount not being fully clamped against the strut tower sheetmetal. Your car clearly has the 5bolt mounts, but who's to say how effective the change ultimately was? You have 5x8mm bolts while I have 3x10mm bolts, so bolt stretch could still be an issue.

    Based on how the clunk sounds, the lack of any other clear root cause, and the odd change to the mount design, I think this is one of the more likely root causes.

    As bushings and tires wear, the loads that go into the upper mount could i crease to the point where the joint integrity is compromised.

    This theory would be difficult to test for and even more difficult to fix though.

The Lower Strut Mount:
  1. Based on advice from other posts, I re-torqued this bolt and the noise went away for about an hour and came right back. This is an aluminum to aluminum clamping joint, which can be sensitive to torque and damage/deformation, so maybe that first re-torque/over-torque was a bad idea. (Some people claim this fixed their issue, at least temporarily, but not verified.)

  2. There are some oddly shaped witness marks on the strut can where it interfaces with the lower clevis on the spindle that indicates that it might not be seating properly, but I've re-assembled this joint several times and the clunk never changes. The marks could also just be from the installation or disassembly process itself. I discovered the other day that there's a special tool BMW specifies to pull the strut into the spindle housing to a specified torque, but I can find the tool anywhere to buy.

    If anyone has machining capability and could make this tool for me to test, PM me.

    Either way, I'm going to clean and reassemble this joint with new hardware exactly as specified by BMW.

Control arms/balljoints:

  1. Again, everything feels tight here, and my thrust arm only has 1000 miles on it. But if the other stuff doesn't work, here are some possible things I'll look at:

  2. The BMW procedure says not to allow the balljoints on the control arms to exceed 25deg of travel during any assembly processes. The easiest way to install struts (the way I did it, or anyone else not following or aware of BMW's requirement) violates this, so it's possible they are damaged, even though they feel tight. I have not loosened these joints for further inspection yet. Once I get through my work plan with the strut, I plan to replace the thrust and tension arm, then duplicate any replaced parts on the passenger side for symmetry. (Some people claim that replacing control/thrust arms fixed their issue, at least temporarily, but not verified)

  3. BMW procedure also says to torque the control arms at curb position with load on the suspension. Not doing this can cause the bushings to wear very quickly and change the way loads are distributed through the chassis. I don't know if the shop did this, so I'll be checking it once I get through my current testing related to the strut.
__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)

Last edited by Racer20; 09-12-2019 at 08:57 AM..
Appreciate 7
      07-24-2019, 07:50 PM   #2
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Next steps (the easy stuff):

1. Edit: Done, didn't help. I just finished the dyno test of my strut this afternoon; now I have a brand new upper mount and brand new assembly hardware, including new sealing gaskets at the upper strut mount mating surface. Hopefully a new rubber bushing and correctly torqued bolts will fix it. I'm going to reassemble everything as carefully as possible to factory torques and test on my test bump.

2. Edit: Done, didn't help. If noise persists, I'm going to remove both the sway bar end links to eliminate the sway bar as a possible cause/transfer path.

3. Edit: Done, sort of helped. Maybe the tension arm? If noise persists, I have a set of chassis ears that I'm going to try to help pinpoint the noise.

4. If noise persists, I'm going to replace the tension arm and control arm (they are not too expensive and easy to replace).

5. Install the friction disks to minimize chance of wheel or rotor movement

Even more next-er steps (not as easy):

1. Edit: Bought the tool, haven't used it yet. Fabricate the special BMW spreader and puller for the lower strut to spindle joint

2. Replace strut/spindle to verify lower strut joint integrity

3. Replace wheel bearing (dealer?)

4. Take to dealer for diagnosis (out of warranty and low chance of success beyond what I'm already doing, unless the issue is in the steering gear)

5. Modify my strut tower to accept the updated 5 bolt upper mount
__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)

Last edited by Racer20; 08-11-2019 at 01:21 PM..
Appreciate 3
David0ff937.50
co_pa13.50
guess2098197.00

      07-24-2019, 07:51 PM   #3
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Looking closer at my drivers side strut tower from underneath as well as the original gasket, it's apparent that the clamp load isn't uniform around the entire surface.

The outboard bolt hole (top-right hole) has less gasket material transferred than the two inboard holes, possibly indicating less clamping pressure.

180deg opposed to the outboard hole is a keyhole cutout of the sheetmetal for some reason, and outboard of that is a witness mark that looks like some dirt rubbing against the sheetmetal (the light brown mark right at the edge of the flat part of the tower). This could indicate a gap allowing dirt to enter then relative motion between the two surfaces causing the brown mark.

Looking at the gasket, there's some small dirt particles stuck to it in this same area, and only this area, the rest of the gasket and tower surface are clean as can be.

Seems at least plausible that the top mount is moving or pivoting about the axis created by the two bolts that have the darker green gasket material around them.

Interestingly, the passenger strut tower's bolts are rotated a bit compared to the drivers side to make room for the negative jump start post . . . they aren't perfect mirror images. So the load path and clamping deficiency that would cause this issue are going to interact differently on that side of the car.

This would mean that the integrity of this joint will be highly dependent on torquing procedure, bolt stretch, and the load mitigation capability of the suspension itself. All things that lead to aftermarket parts (or even non-factory installation of OEM parts) potentially causing problems.

With all the aluminum in this suspension, replacing bolts when specified and torquing to correct specs is absolutely critical for proper performance.

Anyone have any ideas for how to test for relative motion between these two surfaces or fix it either temporarily (to verify the root cause) or permanently?


[IMG]
View post on imgur.com
[/IMG]

[IMG]
View post on imgur.com
[/IMG]
__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)

Last edited by Racer20; 07-24-2019 at 08:09 PM..
Appreciate 3
David0ff937.50
clutchdj525.50
guess2098197.00

      07-25-2019, 09:35 AM   #4
David0ff
Combined Applications Group
David0ff's Avatar
Canada
938
Rep
618
Posts

Drives: Lada Scrapus Trofeo R
Join Date: Jan 2014
Location: Classified

iTrader: (1)

I have chased this issue several times
2018 stock m4 , new lease 90k
clunks at low speeds sometimes

I installed HR Super sports, took everything apart, torqued back to speck... still clunks sometimes..

I think that there is sufficient space between the spring and top plastic plate where the spring hits it, I will felt tape that area around so the spring sits tighter on it.
__________________
/////////
Appreciate 0
      07-25-2019, 10:27 AM   #5
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Quote:
Originally Posted by David0ff View Post
I have chased this issue several times
2018 stock m4 , new lease 90k
clunks at low speeds sometimes

I installed HR Super sports, took everything apart, torqued back to speck... still clunks sometimes..

I think that there is sufficient space between the spring and top plastic plate where the spring hits it, I will felt tape that area around so the spring sits tighter on it.
Thanks, report back once you finish!

If possible, can you take some pics of the underside of your strut tower like I did?

How much did the H&R's lower your car? Do you think the spring is coming unloaded at or near full droop?
__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)
Appreciate 0
      07-25-2019, 10:34 AM   #6
David0ff
Combined Applications Group
David0ff's Avatar
Canada
938
Rep
618
Posts

Drives: Lada Scrapus Trofeo R
Join Date: Jan 2014
Location: Classified

iTrader: (1)

Quote:
Originally Posted by Racer20 View Post
Thanks, report back once you finish!

If possible, can you take some picks of the underside of your strut tower like I did?

How much did the H&R's lower your car? Do you think the spring is coming unloaded at or near full droop?
I will add pix of the car when I get home tonight or tomorrow, but the lowering is perfect, 1/4" wheel gap everywhere but I'm also running 275&285/30/19 tires on oem 437Ms with 15mm spacers everywhere.

I'm using H&R Super Sports for F30, from my old 340.

Funny you mention unloaded spring, I noticed the clunking is more present in comfort suspension ( lower rebound damping) I always suspected that the lower "hold" on the spring during rebound may cause it to shift slightly, which is why I wanted to pad that area with that insulating foam you put around windows (pic attached). I'm planning on applying it to black plastic the top plate area on the vertical portion, I need to find a thin one as the dust boot needs to slide over it.

Ill take pix next time I service the area.
Attached Images
 
__________________
/////////
Appreciate 1
Racer20839.00

      07-25-2019, 10:42 AM   #7
clutchdj
Major
526
Rep
1,270
Posts

Drives: a few cars
Join Date: May 2015
Location: the lower outskirts of nYc

iTrader: (5)

This noise drive me crazy on my f80. Low speed clunk over bumps. Only the front left wheel. Stock suspension and modded same thing.
Appreciate 1
Racer20839.00

      07-25-2019, 12:50 PM   #8
Alan l.
Major General
Alan l.'s Avatar
2888
Rep
7,155
Posts

Drives: 2018 Individual M3 6MT
Join Date: Jun 2009
Location: United States

iTrader: (9)

My 2018 zcp has the same clunk on the driver side that i've been chasing. Its always had this noise since the car was new but not sure if it was before or after I got the MS springs installed since i had them installed on day two of owning the car.

I've tried tightening all of the suspension bolts and nothing has worked so far. clunk only happens over sharp bumps going slow speeds. More so if the wheel is turned.

Things I've tried...

Replaced the top hat
Replaced the gasket between the top hat and chassis
Replaced the sway bar end link
Replaced the collar bolt that holds the knuckle to the strut (tightening this fixed the clicking sound issue for me in my other thread. The recommended tq isn't enough but low speed clunking sound isn't affected)

Does not change the clunking at all. All the work has been done by me so I am very familiar with the suspension now and that its done right.

My next step is to check the two bolts that holds the steering rack system to the car. 4DRS55 said that fixed the clunking issue for him. Trying that fix tomorrow so I will report back.

Alan
__________________

Last edited by Alan l.; 07-25-2019 at 03:31 PM..
Appreciate 3
Racer20839.00
David0ff937.50
clutchdj525.50

      07-25-2019, 03:03 PM   #9
mindspin311
Private First Class
120
Rep
184
Posts

Drives: BMW
Join Date: Oct 2018
Location: Atlanta

iTrader: (0)

How do those 3 holes orient with the car? Which is facing forward, etc?

First thought is the surface just isn't flat. From there, the strut mount wasn't torqued down in any certain way, and left a gap in at your top right mount hole. The clamp force on the other 2 is so strong that the 3rd torqued out and everything seemed fine per torque values, but really there is a gap, evidence by less gasket transfer.

In reality, the mount is pivoting on that axis you called out when you apply near 1000lbs on that one corner at certain points.

Or, is the strut mount not flat, somehow it's bowed out and creates that axis?
__________________
2018 Avus Blue ZCP
Appreciate 1
Racer20839.00

      07-26-2019, 04:20 PM   #10
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Quote:
Originally Posted by mindspin311 View Post
How do those 3 holes orient with the car? Which is facing forward, etc?

First thought is the surface just isn't flat. From there, the strut mount wasn't torqued down in any certain way, and left a gap in at your top right mount hole. The clamp force on the other 2 is so strong that the 3rd torqued out and everything seemed fine per torque values, but really there is a gap, evidence by less gasket transfer.

In reality, the mount is pivoting on that axis you called out when you apply near 1000lbs on that one corner at certain points.

Or, is the strut mount not flat, somehow it's bowed out and creates that axis?
Here's a diagram. A sharp compression impact will cause the wheel to move rearward and inboard in an arc centered approximately about the inboard control arm bushing. The arc is exaggerated on my diagram, but a large enough impact could align the load with the direction that would allow some play at the upper mount.

I'd be pretty surprised if BMW screwed this joint up this royally, but I'm not seeing anything else obvious. This is obviously why they went to a 5-bolt mount, but hearing from some 2018 owners in here, it's clear that it didn't solve the issue and there's still some variation or clamp load sensitivity that there shouldn't be.

As I said, next step is to bolt everything back together as cleanly as possible. I'm going to tighten in multiple stages to try to get even clamp load, but I'm going to do it in an order that ensures that if there is any unevenness due to bolt torque, it's in a direction that opposes the wheel loads.

__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)
Appreciate 0
      07-26-2019, 06:07 PM   #11
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Edited the top post to add a video of the issue.
__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)
Appreciate 1
David0ff937.50

      07-26-2019, 10:02 PM   #12
Alan l.
Major General
Alan l.'s Avatar
2888
Rep
7,155
Posts

Drives: 2018 Individual M3 6MT
Join Date: Jun 2009
Location: United States

iTrader: (9)

Update.

Just spent some time under my car while it was on ramps to check out the steering rack system to see if anything was loose. The two bolts that hold the rack seems tight on my car so doubt thatís the issue. I gave it another half turn to make it tighter just for good measure. While I was under there with the metal pan off I was tapping around to see if anything seems loose that would make the noise that I am hearing and noticed that the long steering column rod could be the culprit. Itís not loose but there isnít enough tension on it so if I just gently tap it with my hand you get this noise. It makes sense because majority of the people here all complain about the clunk sound only on the drivers side.

Sorry for the crappy video. I was laying on my back on the floor trying to maneuver the phone around tight quarters and also show the exact location I am talking about. I wonder if there is a way to adjust the length of the steering column rod just a hair to add enough preload so it wouldnít resonate vibration like it does now.


Last edited by Alan l.; 07-26-2019 at 10:08 PM..
Appreciate 0
      07-26-2019, 10:06 PM   #13
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Quote:
Originally Posted by Alan l. View Post
Update.

Just spent some time under my car while it was on ramps to check out the steering rack system to see if anything was loose. The two bolts that hold the rack seems tight on my car so doubt thatís the issue. I gave it another half turn to make it tighter just for good measure. While I was under there with the metal pan off I was tapping around to see if anything seems loose that would make the noise that I am hearing and noticed that the long steering column rod could be the culprit. Itís not loose but there isnít enough tension on it so if I just gently tap it with my hand you get this noise. It makes sense because majority of the people here all complain about the clunk sound only on the drivers side.
I did the same thing last weekend. I got a kind of springy resonance sound like when you tap the coil springs, but not that loose rattle/knock sound that you seem to have. If my damper reinstall doesn't fix the issue, I'll take the reinforcement plate off and check the steering linkage again.
__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)
Appreciate 0
      07-27-2019, 10:08 PM   #14
jzmundy
Major
jzmundy's Avatar
558
Rep
1,206
Posts

Drives: G01
Join Date: Jan 2008
Location: Raleigh, NC

iTrader: (6)

I just noticed this same clunk in my F80 and it drives me nuts. Staying tuned to this thread. Thank you for such a detailed contribution!
__________________
Then - 2001 E53, 2005 E85, 2007 E92, 2013 E82, 2017 F80
Now - 2016 F15, 2020 G01
Appreciate 1
Racer20839.00

      07-27-2019, 10:11 PM   #15
jzmundy
Major
jzmundy's Avatar
558
Rep
1,206
Posts

Drives: G01
Join Date: Jan 2008
Location: Raleigh, NC

iTrader: (6)

Quote:
Originally Posted by jzmundy View Post
I just noticed this same clunk in my F80 and it drives me nuts. Staying tuned to this thread. Thank you for such a detailed contribution!
Just adding to this, my car:

2017 F80 ZCP
MPHAS set to BMW recommended heights
Alignment to spec
__________________
Then - 2001 E53, 2005 E85, 2007 E92, 2013 E82, 2017 F80
Now - 2016 F15, 2020 G01
Appreciate 0
      07-31-2019, 06:51 AM   #16
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Quick update:

Reinstalling the strut with a new upper mount carefully with all new hardware fixed it . . . For about 20 minutes.

Everything felt tight and the feeling of increased harshness was gone until I hit a particularly large pothole-ish crack, then something loosened and it was back.

Trying my test bump at different angles, the noise goes away if I hit both wheels at exactly the same time and gets worse as I go off-angle and get more single wheel articulation.

This leads me to the stabilizer bar link. It's tough to get full torque on this part, but I've ordered a new one and new nuts, I'll update when I get them installed.
__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)
Appreciate 0
      07-31-2019, 09:20 AM   #17
Alan l.
Major General
Alan l.'s Avatar
2888
Rep
7,155
Posts

Drives: 2018 Individual M3 6MT
Join Date: Jun 2009
Location: United States

iTrader: (9)

^^ i would agree that if I hit the bumps with both wheels there is no clunk present. Its only when its the driver side wheel alone I notice it.

I had a friend that is a BMW mechanic check out a M4 that he was working on to see if the steering rod that seemed loose on my car was the same on that one. He took a video to show me and it sounded the same when he tugged/tapped on it so leads me to believe its not that.
__________________
Appreciate 0
      08-01-2019, 06:30 AM   #18
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Minor update:

Got under the car again and cranked down on the sway bar link nuts. No improvement.

Ordered new bushings for where the bar attaches to the body just in case those are worn.

Incidentally, my dealer will sell me the puller tool to properly seat the strut into the spindle for $138. I might try that as well, but shipping from Germany will take about 3 weeks.

Edit: ordered the tool this morning along with the spreader socket.
__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)
Appreciate 1
jzmundy558.00

      08-01-2019, 08:02 AM   #19
jzmundy
Major
jzmundy's Avatar
558
Rep
1,206
Posts

Drives: G01
Join Date: Jan 2008
Location: Raleigh, NC

iTrader: (6)

Quote:
Originally Posted by Racer20 View Post
Minor update:

Got under the car again and cranked down on the sway bar link nuts. No improvement.

Ordered new bushings for where the bar attaches to the body just in case those are worn.

Incidentally, my dealer will sell me the puller tool to properly seat the strut into the spindle for $138. I might try that as well, but shipping from Germany will take about 3 weeks.

Edit: ordered the tool this morning along with the spreader socket.
When you say deep dive, you ain't kidding.

Thanks so much for taking the lead on this.
__________________
Then - 2001 E53, 2005 E85, 2007 E92, 2013 E82, 2017 F80
Now - 2016 F15, 2020 G01
Appreciate 1
Racer20839.00

      08-01-2019, 08:14 AM   #20
icegrill
Lieutenant
icegrill's Avatar
298
Rep
558
Posts

Drives: 2015 M3
Join Date: Jan 2018
Location: Oregon

iTrader: (0)

This is awesome! Way to take the bull by the struts🧐
Appreciate 1
Racer20839.00

      08-02-2019, 04:39 PM   #21
Racer20
Major
United_States
839
Rep
1,119
Posts

Drives: F80 M3, 228i THP, E46 ZHP
Join Date: May 2009
Location: Ann Arbor, MI

iTrader: (0)

Possibly significant update:

I drove the car for about an hour and a half last night in all modes on all types of roads, and it was generally pretty quiet. Only during the first few minutes and last few minutes did I hear the clunking.

The lack of consistency led me to take another look at the test data from my ZCP struts from before I installed them. I found a minor issue that MIGHT be the smoking gun (further testing required):



This graph shows the damping force produced over one complete cycle (75mm rebound stroke then a 75mm compression stroke) at high damper speed and at a very soft amperage setting (as it would be when driving at low speed or on a reasonably smooth road)

Ideally, this curve would be smooth and rounded with no discontinuities, like the black line (my passenger side strut). However, the driver's side strut (the noisy side) exhibits a little bit of damper lag in compression.

That means that if the impact is large/sharp enough to reach high piston speeds, the damper is not building force properly during the initial portion of the stroke. That means energy is not being dissipated, and suspension loads and velocities can be much higher than intended.

Damper lag is a bit of a "chaotic" phenomenon . . . once it occurs a little bit, it tends to amplify itself and become very unpredictable. It's also highly dependent on the road profile, temperature, and other suspension parameters (ride height, jounce bumpers, etc.) Considering that my damper test is done at "standard conditions," it's not clear if this lag would be better or worse during actual use under the conditions that create the noise on vehicle.

It's also not clear that this lag will actually cause noise on the vehicle, as all dampers will exhibit lag under some conditions, and some vehicles are not very sensitive to it.

This data is from when I bought the ZCP dampers used with ~6k miles on them. I need to take them off again and test them under more dynamic conditions to see if the lag has deteriorated in the ~2000 miles that I've put on them.

The challenge here is that there are many possible causes for lag. Some dampers inherently lag when new due to the length or valve setup. Some dampers can lag if the tolerance stack up of the internals is over some threshold, (meaning some will and some won't), and some dampers won't lag unless something is worn or damage.

It's also possible that ride height, alignment, or the different loading of aftermarket springs contributes to the lag to some extent, but I have no way to know that at the moment.

So, with the data in front of me, I can't say whether buying a new strut will solve the problem, or for how long. It's possible that a brand new strut will show the same amount of lag.

I'm hesitant to spend $1200 on a new strut just to have the noise come right back.

Maybe a long shot, but if someone has some ZCP shocks/struts laying around and would be kind enough to ship them to me, I could test them to get a larger sample size of this problem. Then we could see if the clunk and the lag were correlated. Of course, I'd ship them back to you as soon as I'm done testing.
__________________
2015 M3, 2005 330i ZHP, 2015 228i 6MT Track Handling Pack, 2007 M Coupe (Sold)
Appreciate 1
David0ff937.50

      08-02-2019, 06:41 PM   #22
swagon
Brigadier General
swagon's Avatar
No_Country
4532
Rep
4,842
Posts

Drives: E82|F80|6MT
Join Date: Jun 2013
Location: .

iTrader: (0)

I believe I have the same clunk on an f80 with non-adaptive suspension. Car fully stock.
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 02:00 PM.




f80post
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST