Do rear coil springs sag after 21 years?

[bkirk]

Having just finished a cooling system and CCV refresh, as well as having mounted new Bilstein shocks and OEM springs on the front, my mind is wondering if there is any benefit in replacing the rear coils since the PO replaced the rear shocks two years ago. Do the rear coils develop any sag after 21 years?

[Vintage42]

No. Negative camber is original equipment.

[BladeRunner919]

They have a tendancy to snap the last coil, but it's not always obvious until you take them out.

[bkirk]

Do many folks replace their rear coils?

[ThatZ3Guy]

I don’t know that there’s really any reason to replace them unless you want to change the ride height. I’m no expert by any means

[BladeRunner919]

I did because one was snapped, but wouldn't have done so otherwise. They're not expensive and pretty easy to do.

[magnetchief]

I replaced mine.
But only to change the ride height.

Sold the original M coils on.


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[Meeners]

Every coil spring sags/settles over time, just like leaf springs. That's metallurgy dependent. This is likely why installing new front springs made you notice the slight sag in the rear. It may be very slight but old springs are weaker than when new because of steel's strain curve. Thousands of repetitions result in yield, until they eventually break. Most people use this opportunity to upgrade or lower their cars with aftermarket springs/coils however, if you have the means and you can replace them with stock go ahead. Just keep in mind the rubber parts lose their rebound over time as well, not just the springs.

[bkirk]

Every coil spring sags/settles over time, just like leaf springs. That's metallurgy dependent. This is likely why installing new front springs made you notice the slight sag in the rear. It may be very slight but old springs are weaker than when new because of steels strain curve. Thousands of repetitions result in yield, until they eventually break. Most people use this opportunity to upgrade or lower their cars with aftermarket springs/coils however, if you have the means and you can replace them with stock go ahead. Just keep in mind the rubber parts lose their rebound over time as well, not just the springs.

Thank you!