VVF

+1, knocking when tapping the brakes is most probably control arm bushings.
You can test this by going slow, turning the wheels slightly and tapping the breaks with moderate force every second or so.

Meca

I did not change the sway bar bushings, because when we initially ordered them, they arrived but couldn't be fit on my sway bar. Don't know how's that, they were different than mine, so we returned them and never ordered another ones, because current ones looked good.
I could be wrong.

Wait wait wait wait...
We did exactly that - tightened (and tightened them well) while the car was on the car lift.
How could you tighten the bolts while the car is on the ground ?

Sh*t, I just looked at this video:


and saw a comment from some guy called "pkaffe" in the comments below...looks like you were right...
So, I guess we ruined the control arm bushings?
Which ones, because we changed all 4 ?
Anything else?

Ah...shhhhhhhhhh man

jkowtko

Argh! Yes that is a good suspect then. Unfortunately all four.

To tighten under load, you can either (a) use a jack to lift that suspnesion link until it starts to lift the car, or (b) do like I did and drive the car up on ramps, loosen and retighten the bolts. You can actually move the car with the bolts just snug, or say just 10 ft-lbs of torque, enough to keep them from rattling ... the suspension won't fall apart, it may just make some shifting noises.

So for starters I suggest you try loosening and retightening the bolts while the suspension is loaded, just to see if there is still any spring in the rubber that will be released. It's always possible that the one or more of the bushings will still work. Unfortunately the more likely scenario is that you will see tears in the rubber from the excessive stretching.

Meca

Thanks for that, didn't know it.
I'll report back once I find time to investigate.
Thanks again!

jkasso11

Hi Mecca,


I have a very similar problem to yours. Were you ever able to find out the cause?


Thanks,


John

Meca

I'm not getting any knocking now John, so I don't really know what to tell you since I changed almost everything I possibly could down there.
However, it's still summer temperatures here, but I bet you that knocking will return soon, once temperatures drop since it is somehow sensitive to temperature change.
For example, before the summer, the knocking was usually especially loud during cold starts, but once you drove for 10-15km it would diminish...mostly.

I suggest you change the cheapest bushings first, such as those of a steering rack, sway bar, etc. and see if it makes any change.

jkasso11

Thanks for your quick reply, Mecca! Your issue is similar to mine. I took off the wheel today and had my friend take a quick look at the suspension components. He didn't see anything out of the ordinary. However, the shim pad on top of the brake pad of the front left wheel was almost a centimeter off line. This might be causing a friction problem with the brake. So, I am going to change out the brake pads this week to see if the sound/knock feeling goes away. If not, I will be checking out the control arm bushings in more detail


Thanks again!

Meca

Could you please tell me more about this shim pad and what it is? Do you perhaps have a picture of it so I can check it too?

My rotors are constantly getting warped, I've already straighten them 2 times now, and I drive slowly and easy on brakes.

It might be connected...

Thanks

jkasso11

Hi Mecca,
On the outside of the brake pad there is a thin metal sheet that goes between it and the caliper. Mine has just slightly dropped about half a centimeter or so off of the brake pad. So, this might be causing some of the problem I am having. Though I don't know for sure, I need to fix it anyways. My hope is that it will stop the sound.




I should have taken a photo, but I didn't. This week when I replace it, I will take a photo and let you know how it goes. As far as google images goes, you can see on the bottom of this brake pad there is a thin metal plate. This is what is slightly displaced between my brake pad and caliper. Ignore the yellow lines and worn brake pad.

Meca

Great, thanks, I'll have it checked with my mechanic. Let me know if that stopped your rattling.

Gregor12

What's up everyone. Just joined because I had the same issues. However. Mine surfaced after a normal brake job. Drove me nuts. Checked everything over and over but couldn't find anything. Swapped pads. Re-installed and cleaned everything. Checked bushings. Torqued everything. Still got a noticable thump or knock under medium and heavy braking. Pedal didn't move. But felt like someone was hitting the frame under my feet with a hammer.

Ended up being the Bosch rotors that I got. Switched back to whatever was on my car before and it went away. I'm guessing the rotor was shifting on the lugs under hard breaking. I advise everyone to torque everything down properly after cleaning the hub and rotor surfaces. good luck

Phil

Meca

Great, thanks for your advice.

I also have one advice, not related to this topic but rather to brakes in general.

For one year I had ATE rotors with Mercedes (I believe those are TRW) pads.
They constantly warped. I straightened them 3 times and they still warped.
There was no heavy braking or high speeds included, just normal everyday use.

A few days ago I swapped them for original Mercedes rotors with Mercedes (TRW) pads.

So far so good, after a few hundred kilometers of burn-in period, they acclimatized and are performing flawlessly.

So, from now on, I'm putting only the original Mercedes parts on my car, no matter the cost.

Gregor12

Sweet. Good to know! Did you ever get your knocking issue solved? And I read somewhere that the original Mercedes rotors for the w210 were brembos? Who makes the rotors that you purchased? I understand you said original Mercedes but I'm not sure if they make them through a thirds party or not.

Meca

I can't hear the knocking now, maybe when weather gets colder here.

I've read the sticker on rotors while they were new, it said "Made by Daimler-Benz".
I guess it can't get more original than that

jkowtko

Meca, just curious -- did you ever retighten your control arm bushing bolts with the suspension loaded? If so, how did that affect the knocking noise?

Thanks. John

Meca

Yes, they retightened them, it's standard procedure..
Btw. the knocking is still here. Gonna have to take it to certified MB service center and see what they have to say.

EOB

Been following this very insightful thread as I am experiencing a similar problem - rumble noise on front left side when making a sharp right turn or braking heavily. Have replaced sway bar bushings (which, unfortunately led to a stripped bolt on each of the brackets; should be a relatively easy fix with bolt and nut as solution), upper control arms replaced, and installed new pads and rotors. The rumbling is not as noticeable as before, but still there when the car is in a sharp right turn or in a strong down-braking condition. Will be replacing the lower control arms in a couple of weeks and learned from this site that it is important to pre-load the suspension before torqueing down the bolt at the bushing and the nut on the ball joint. Since I might have access to a drive on lift next to where I will be doing the work on a two post four leg lift, do you think it would be safe to maneuver, back out and turn the vehicle and get it in position to roll up on a runway lift to complete the torqueing?

jkowtko

Yes, I don't think it's a big deal if you have the bushings twisted for a short while (in your case only a few minutes). Initially tighten the bolts only slightly, just past snug, so they don't shift so much when you move the car.

Meca

This is exactly what I'm experiencing as well!
Most noticeable when doing a sharp U-turn under braking.

jkowtko

Is it rumbling or knocking? If rumbling (continuous) I would suspect a wheel bearing.

Meca

I know what you mean, it's not the wheel bearings.
It's knocking, sometimes even when turning wheel to extremes while standing still.
It could also be steering rack end bushings (don't know the exact translation, those things on the end of the both sides of steering rack, near the wheel), although it's weird because we've checked them and there's no play in them, also not while turning the wheel.
It's driving me mad already for so long that I'm either gonna get used to it, get it solved somehow or sell the car!

jkowtko

If you are standing still and hearing a clunk when you turn the wheel lock to lock, that is usually the shifting of a ball joint. Each control arm has a ball joint, so presumably if you replace the entire control arm (not just the bushing) you will also replace the ball joint. The "steering rack end bearings" you are talking about should be the tie rod ends, which have a ball joint at the steering knuckle. There is also a bearing at the top of the strut that allows the steering assembly with strut to turn.

If you can have someone stand outside the car with the hood up and listen closely to the top of each strut, maybe they can detect if the noise is coming from within the top rubber mount of the strut (strut bearing, comes with a full strut mount assembly) or is further down (ball joint).

If you suspect ball joint, then have them get underneath the car and touch/hold the control arm or tie rod end while you are turning the wheel, and they should be able to feel the clunk pretty strongly on the part that contains the failing ball joint.

Meca

Yes, it could be ball joints.
So far we've replaced 3 control arm bushings, but only 1 arm was completely new (therefore 1 ball joint), which means it could be one of the remaining 3 ball joints

We machine pressed those bushings in, but ball joints couldn't have been replaced, they come new only with whole control arm new.

So basically, I should now buy 3 complete new control arms ? Even though we tested all of them (while the car was on the lift) and there's no play in them?

What a cruel world and sneaky business strategy from Mercedes

jkowtko

I think people generally expect the ball joints to last 2x the bushings ... and you can replace bushings without removing the control arm completely from the car ... so theoretically it's a much faster and less costly procedure (if you have the $200 ball joint press kit!)

Since you've already done the bushings, don't replace the arms unless you've determined that one of the joints is clunking.

But, yes, I just replaced the entire arm when I did mine. Granted removing the uppers requires unbolting the strut from the knuckle.

VVF

Yep, that's called throwing parts at it Could end up quite costly.
However, I went to an indy shop with a clunk in LHS front somewhere, and they were happy to charge me $100 without finding the reason. Everything looked solid to them.
So at least you save on labor if you do it yourself because those *ckers would just throw the same parts at the problem!