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Suspension/Steering Knock...driving me crazy.

22572 Views 84 Replies 16 Participants Last post by  amosfella
Making a new thread for consolidation and update...
I am still fighting this slow speed knock on my 2008 E350 4Matic (123k). Im completely unable to replicate when under the car... its driving me crazy.

Noise comes from Front, unable to differentiate a side.
It "knocks" or "pops" when coming on/off a curb. (can replicate over and over)
sometimes changing from Reverse to Drive if ground is not flat
sometimes does it driving straight out of the garage into the normal driveway slope.
sometimes "pops" when you step into the car and sit down with some weight. (cannot replicate after it pops once, wont do it again)

Parts replaced:
Sway Bar End Links
Upper Control arms + Ball joints
Lower Control Arms + Ball Joints
Both Engine Mounts + Transmission Mount
Steering Rack bushings.

Tests done, and no difference made
Disconnected sway bar, no change.
Disconnected both tie rods, pushed and pulled all over, no slack.
Grabbed both tires at 9/3 and 12/6 and no slack.

I'm almost at the point of throwing my hands up and taking it to the dealer.
Anybody got anything to throw some ideas my way?
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I can't wait for your update on the Steelman!
I continue to be impressed with the ingenuity and DIY fire that forum members show. You figure that there has to be a tool out there to locate and isolate car noises using Bluetooth or equivalent technology and then ps2cho posts what you were thinking about. Thanks for the troubleshooting idea.
Spent all morning working with the Chassis Ears. Definitely needs some patience to use it...

First, I attached to tie rods, the body of the steering rack:
> you could hear it in the background, but the "sensitivity bars" on the device did not reflect any noise.

Second I attached to the front driveshaft case
> Louder, but the sensitivity bars did not reflect much.

Third worked with the lower ball joints on both sides.
> Even louder, but still felt like it wasn't the part.

Fourth attached to the front subframe (near where the subframe bolts are).
> Definitely louder! Thought I had found it and was possibly front subframe mounts...

Fifth, I wanted to be 100% sure I attached on the subframe next to the rear-most lower control arm mount
> VERY Loud!!
Went back and this time attached the probe directly to the lower control arm bolt.
> Same volume, but the noise was much clearer and more precise sounding.

Got under, and the rearmost passenger lower control arm bolt was not fully tight. I went under and retightened to 110nm. Essentially 90% solved!! Still a noise small knock though...

I say 90% because after I rechecked all lower control arm bolts and torqued to 110nm, there is still a knock, but its very slight. Now that I am no longer getting an overpowered creaking noise, I can focus in on this. The knock, now seperated from the LCA bushing noise, sounds to me like it could be the sway bar bushings. That will be easy to isolate.

I can probably be very clear that the WIRELESS version is superior to the WIRED, solely because of the sensitivity bars. It picks up background noises, but unless the vibration is on the clamp, the sensivity reader won't spike, so you know the noise is not very close. I think that made a big difference figuring it out.
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That was good work finding one of the noise sources and fixing it. How do the Steelman probes work exactly? You mentioned a clamp. Is that a clamp that holds the monitor in place? Do the monitors use a microphone or is it a piezoelectric type device or something else? Any information that you can provide will be appreciated since I'm thinking of buying one myself.
My fool proof old fashioned way of finding suspension clunks is to use a plastic shot-filled dead blow hammer, and wack each component. the lack of a "ping' from the hammer makes it ALOT easier to hear any slight clunk from components. had a similar problem with my sisters E320 Bluetec, from the same area! it was a worn bushing that was nearly invisible to see the condition of on one of the front thrust arms!
Well I’ve spent a good number of hours with the chassis ear...I believe the noise is still coming from the lower arms. At first I thought it could have been the steering rack, but the probes attached to different parts of the rack yielded no clunk, although the noise was still audible in the background.

I need to build a wheel platform out of 2x4’s to gain some more ground clearance since I’m unable to get my big torque wrench in on the lower arms with my regular ramps since the weight needs to be on the ground when tightened.

The LCA’s are 110nm torque...

My car came with ONE single adjustable control arm bolt and I ordered the stock unadjustable bolt since I’d like to return back to factory now. I will keep the old one but with the camber on both sides looking good now it’s not needed.

The chassis ear has been a great tool to eliminate parts.

It’s frustrating to me the noise is STILL seemingly coming from the LCA’s (both sides...). The arms were both new 15k ago and noise started 5k after I installed them. I find it incredibly unlikely both arms failed. The rubber visually looks new still.
Makes me feel like somehow it’s not torqued even though it feels like it’s tight enough. But can’t be 100% until I can get the torque wrench on it. I tried to hand tighten to match the lug nuts, but who knows.
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Continued saga....

Decided to get a better look at the lower control arm bushings again. I think another silly mistake due to originally torqueing the LCA bolts while in the air...

The GOOD thing is that I already have the Genuine MB lower arm/transverse bushing kit in my parts box! I bought it originally 3 years ago, then when I realized it didn't come with the bushing where the strut attaches, I bought the entire A-arm instead and figured I could resell the kit (which never got any luck!).

This is on the passenger side, which according to my ear, is the quietest side. I'm betting the driver side bushing is even worse and hopefully this is the noise!

Going to get both arms removed and see if I can get the bushings out and new ones pressed in with adapters I have in the garage, otherwise I'll have to buy a tool.
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Harbor freight has a 20 ton press always on sale, but not cheaper than buying a new arm.
Ok update!

Driver side bushings were OK, passenger was pretty worn. Replaced both.
I ended up buying the KTC tool to press the bushings back in, which worked caveat though is that the tool is really designed for the W210. I also used an adapter from the Astro Master Ball Joint kit (the black adapter used in press photo).

Removal of the two smaller bushings is best done using a punch on the edges. Work it around until it comes out, or work around enough that it has come out a little, then a few big whacks from the back and it comes out.

Installation orientation is important!! The longest side of the bushing must be 90 degree's with the LCA. In addition, there is a gap in the bushing that must face the chassis...In all there is only ONE correct position, don't get it upside down. I took photos of the bushings before removal to be sure I put it back the same way it came out.

Got it all tightened back up (tightened bolts after backing the car off the driveway, and back up to be sure the bushings settled in their driving position) and so far no noises, however I said that last time and then after a few more miles it came right back. Will update in a few days!
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Well after 100 miles over past two days, noise has not returned! I think I can call a success on early lower arm bushing failure, likely due to not torqueing when the car was on the ground. I think the dealer is charging $900 for LCA bushings today, so $100 for the tool and $150 in bushing parts saved me a lot.

It's been a journey so glad finally got it. Downside of course...those rear shocks feel worn now compared to a super tight front end! Maybe next year...
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Your car must be a 4matic then? Standard 2WD lower control arms only have one attachment point to the frame!

I might end up needing to change my LCA bushings on the front end here too, the rubber is showing stress fractures just like yours, but they're not creating noise yet. My thrust arm bushings are a bit worse, I'm going to be changing those next weekend!
Ps2cho, would you rent out your Steelman tool to a fellow member? I have been chasing a rattle in my W211 front for almost 2 years, changed everything twice and no luck.
Ps2cho, would you rent out your Steelman tool to a fellow member? I have been chasing a rattle in my W211 front for almost 2 years, changed everything twice and no luck.
Probably for members that have been on the forums for a while (ie not lending to new or recent members I've never heard of)...

...however due to the fact this tool can be easily damaged between receivers falling off, wires touching ground etc (already did this myself and had to buy spare set of wires), I'd need the full cost of the unit ($220 on amazon right now) held in deposit... maybe $30 to rent (my sanity payment for packaging, worrying if it will get back to me, juggling paypal deposits lol, although I'd give plenty of time for use, ie 2-3 weeks.) + $15 shipping since it won't fit in any flat rate boxes,
So would be kind of an expensive route > ie: $40 + 30 shipping to&from cost to rent for you assuming returned like it was sent. Food for though though.
I've been a member for 11 years but you are right, it doesn't make sense. It is just that I do not want to throw more money at it.
Update -- Not a single noise all week!

Next up is to get the car aligned. I plan to use a local shop and have the car aligned without use of any alignment bolts as I want to see how everything looks without manipulation after I changed the steering knuckle, lower arms etc.

I'm expecting both Camber and Caster to be good, but will be interesting to see. I will likely replace my rear shocks next year along with some fresh tires, and at that point I'll take it for the dealer alignment to get it 100% fresh.
Are you using all Genuine MB parts or OEM?
Are you using all Genuine MB parts or OEM?
All MB parts used! 4matic has a number of stuff that has no OEM anyway such as Lemfoerder etc...
Well you can't say I didn't nail it!! Prior to going to the local shop /w a hunter alignment machine, I fully filled up the gas tank and pressurized all tires to spec.
Dead perfect up front! I think that probably wraps up this saga now :D

Prior alignment (last time aligned in 2016) when I realized something was off:

Alignment this morning:

Can't really know for sure if the rear camber change if related to gas tank fill (no idea if it was full or not in 2016) and how it was loaded, or if a sign of minor wear, but not concerned since no odd tire wear patterns.
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Your car must be a 4matic then? Standard 2WD lower control arms only have one attachment point to the frame!

I might end up needing to change my LCA bushings on the front end here too, the rubber is showing stress fractures just like yours, but they're not creating noise yet. My thrust arm bushings are a bit worse, I'm going to be changing those next weekend!
Do I misunderstand you? I have 2 control arms per side, a leading and trailing conrol arms. Both attach to the subframe and the other ends attach to the steering knuckle via ball joints. This is on 2w rear drive.
Well, upper arm still looks brand that didn't pan out. I'm about at wits end and going to just hand it off to the dealer to figure it out. Going to give one last attempt with the ChassisEars then I'm done with this because I've exhausted almost everything.
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