How hard would it be to replace my sport springs with softer ones?
My sport suspension is starting to loosen my fillings.

 

You will have to do what we did - sell the Sport - buy a Lux version.

 

OP , what mileage ?

 

116000 km

 

Will the LUX springs not fit the sport struts?

 

Dampers...
, big misconception is they're shot when only leaking , they get soft and an under damped spring is a rough ride .

Told my dad this as an occasional passenger his was not good due to dampers , " it's because it's got Sports suspension. "

As he drives it every day he doesn't notice the super slow deterioration in ride quality .

 

but also a stiff spring is a harsh ride too. I should be able to take one spring and replace it with a softer spring. I don't see how this is such a problem.

 

And if you do that you should do the dampers too .

 

The lux version isn't that much more comfortable either. You don't have many options for a more supple ride. All of the aftermarket options are equivalent or harsher.

 

Inspect your control arm balljoints and bushings before jumping to a different suspension setup. If those are worn out, your ride is going to be quite a lot more harsh

 

I just bought the rear "w/o sport" springs to try this and see what difference it makes in the ride. For my year/US model, there are only two rear spring numbers, with or without sport.

I would love to know the actual spec for these things (lbs per inch deflection) but haven't found any info like this for the factory items.

The front is much more complicated, but I believe the 204-321-05-04 (three red marks) may be the "w/o sport" spring. The fronts have fourteen different numbers shown in the MBZ parts catalog and the fitment information is minimal ... so I decided to do the rears first and then decide from there.

 

Quick update on fronts ... I found a helpful dealer parts guy who said he could tell me which springs a car was built with from the VIN number. So I looked around on TrueCar and found five VINs for 2011 C300 "Luxury" sedans (2011 was the last year Mercedes offered a RWD V6 C300 sedan). I looked at the pictures of each of these cars and could confirm from the front grill, hood ornament, wheels and four-spoke steering wheel that they were indeed the "luxury" spec. and therefore should have the less stiff springs.

Each of the VINs I submitted mapped to two-yellow front springs, aka, part number 204-321-04-04. Specs I found elsewhere show the 2011 RWD C300 weighed 3,560 lbs, and my 2014 RWD C350 is listed at 3,616, so it sounds as if these springs will be a pretty close match for the car's weight (the 4Matic car is more than 100 lbs heavier). The only other difference is the sport suspension cars are lower by 0.6 inches/15 mm and I suspect that's all in the springs, so changing to "luxury" springs will probably raise my car a little. But I think it will be barely noticeable, if at all. And the final nuance is that the upper and lower spring insulators vary by spring number, so I'll have to change those too.

The total cost of changing the fronts will be a bit high, so I wanted to be very sure the changeover was feasible and has a high likelihood of working correctly.

Incidentally, on my car I had excellent results when I changed the shocks to Koni FSDs. That alone took away a lot of hardness; the OE shocks were some of the stiffest things I've ever seen on any car. I hoped the shocks by themselves would produce the ride characteristics I wanted but have since found I really need to do the springs as well. Will post again once I have the springs on and can report on the difference.

 

Be sure to let us know how you made out.