W211 Broken Spring Question

[shertex]

The rear springs of my CDI were replaced at 108k miles by PO. Some time ago I noticed that there was a break in both of the springs (this is a known weakness of the W211). But, in both cases, the break is in the bottom-most portion of the spring, perhaps 180 degrees into the first coil from the bottom. As a result, the entire spring is perfectly seated and everything seems perfectly stable.

Is there any pressing need to replace the springs?

[Mxfrank]

A coil spring twists as it compresses. The fact that the springs broke suggests that there is stress at that point. And that the remainder of the spring plays a role in compression. So yes, the suspension is at least somewhat compromised and the springs should be replaced.

[97 SL320]

A coil spring is really a spiral torsion spring.

Automotive suspension coil springs generally have a seat that cradles the coils end as a way to distribute the load. At some point the cradle ends and a high load it placed on the coils wire. ( There are a few other coil end shapes but each can have a similar problem. ) Also, the cradled end is consider the " dead coil " since it does not contribute to carrying the load and the other coils are considered " active coils ".

Sometimes the coils open end will contact the next coil, this results in a notch being worn in an active coil causing a stress riser. Road salt can lay in the cradle causing the springs wire to rust, the weakens the spring and also causes a stress riser.

Broken springs should be replaced as I get concerned they might escape / move on a very bumpy road. A broken coil might slightly reduce ride height and slightly increase spring rate.

[mbolton1990]

Originally Posted by 97 SL320

A coil spring is really a spiral torsion spring.

Automotive suspension coil springs generally have a seat that cradles the coils end as a way to distribute the load. At some point the cradle ends and a high load it placed on the coils wire. ( There are a few other coil end shapes but each can have a similar problem. ) Also, the cradled end is consider the " dead coil " since it does not contribute to carrying the load and the other coils are considered " active coils ".

Sometimes the coils open end will contact the next coil, this results in a notch being worn in an active coil causing a stress riser. Road salt can lay in the cradle causing the springs wire to rust, the weakens the spring and also causes a stress riser.

Broken springs should be replaced as I get concerned they might escape / move on a very bumpy road. A broken coil might slightly reduce ride height and slightly increase spring rate.

Very interesting!
Thanks for sharing

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