C 55 suspension popping noise

[goblintinkerer]

Developed an issue overnight where by the morning I noticed a creaking metallic noise coming from the passenger rear while driving on uneven road. I jacked the car up and saw the spring was bowing and rubbing against the trailing side of the spring arm. I decided to rebuild what I can in the rear so threw some parts on, spring arm camber strut, toe strut etc, however it didn't fix the issue even after alignment. I went down a rabbit hole and eventually brought the car to mercedes to check if the subframe got weak from corrosion over time. The repair for goodwill was declined and they told me to get genuine parts but I knew that wouldn't fix the issue. One thing they told me that the driver side spring is also rubbing on the rear axle but on the leading side of the spring arm, while theres a gap on the trailing side. I narrowed the issue down enough where it didnt matter what i changed from left to right or right to left, the geometry of the suspension stayed identical both sides. The springs sit square on the top rubber stop, new genuine 2 notch variant both side and shims down bottom. I bought replacement springs to test under compression but they would still rub against the arm. This rubbing is making an awful sound in the cabin as its catching and flicking itself off.

Now I'm leaning towards the bushes on the subframe so I'm deciding to get a new subframe with new bushes preinstalled. My theory is that maximum torque output by the engine, the differential wants to rotate counter clockwise in its cradle hence the asymmetry of the springs. With the subframe bushes looking very tired there is nothing really preventing the subframe from yawing

 

[Petrol Pete]

As someone who has replaced the shocks and springs (all round ) on a C55 I have not seen this . On mine I replaced the busing in the hubs as well , but as the spring locates with the upper cup which is part of the body and the lower part of the spring seats in a 'separate' part of the car in the swinging arm which is bolted to the subframe your dilemma would suggest the subframe has 'moved' . In your 3rd photo, is that the shim I can see at the bottom ?

I'm pretty sure the shim(s) on mine were not visible once fully assembled.

Unfortunately I do not have a similar photo to check but I am pretty sure the shim was not as visible under my springs once assembled .


I have many photos of the replacement work but only this one that (kind of) shows how close the spring is in relation to any other part of the car .

For info my car is on 156K miles with the original subframe . How many miles on this car ?





This one , in the hub . It's a bear to remove , I had to do mine as one had 'gone dry' and was making a 'clacking noise' when turning.

 

[goblintinkerer]

yes, third photo is the shim, and the spring is bowing away instead of sitting straight. the tails of the spring do still locate both on top and bottom perfect. the bottom locating peg of the shim is where the spring ends too. the sounds are definitely coming from the springs, i put red tape on the spring where its touching before assembly and it destroyed it already from friction wear. and yes dilemma is the subframe has shifted or the subframe bushes couldnt keep it still anymore. because of the torque the differential wants to turn counter clockwise and won, shifting the rear subframe with it. 128k miles on the car, FSH 3 owners

 

[goblintinkerer]

As someone who has replaced the shocks and springs (all round ) on a C55 I have not seen this . On mine I replaced the busing in the hubs as well , but as the spring locates with the upper cup which is part of the body and the lower part of the spring seats in a 'separate' part of the car in the swinging arm which is bolted to the subframe your dilemma would suggest the subframe has 'moved' . In your 3rd photo, is that the shim I can see at the bottom ?

I'm pretty sure the shim(s) on mine were not visible once fully assembled.

Unfortunately I do not have a similar photo to check but I am pretty sure the shim was not as visible under my springs once assembled .


I have many photos of the replacement work but only this one that (kind of) shows how close the spring is in relation to any other part of the car .

For info my car is on 156K miles with the original subframe . How many miles on this car ?



View attachment 172566

View attachment 172567 This one , in the hub . It's a bear to remove , I had to do mine as one had 'gone dry' and was making a 'clacking noise' when turning.

i replaced the subframe and there is a visible gap now. no more banging, popping. good luck to anyone having the same issue as me.