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Discussion Starter #1
Removing the Sports Package Suspension for the Comfort.

First, I'll define my terms. Comfort or standard referes to the non-sports package suspension. Sport refers to the sport suspension.

My 2010 SLK350 Sports Package road like a dump truck. It crashed over minor irregularities in the road. Any pot hole it might encounter was a dramatic fearful event to be avoided at any cost.

Before going into any details, observe the following numbers. They measure the ride heights before and after changing the front spring from sport to standard. The ride height is measured through the center of the wheel from the garage floor to rim of fender.

Rear Front

Driver 26 1/8" (26 1/8") 25 5/8" (26 1/8")
PAX 26 1/8" (26 1/8") 25 3/8" (25 7/8")

The numbers in parentheses were taken after a couple of hundred miles of driving. Notice the front ride height increased exactly 0.5" the goal of this modification.

Before I go on, I want to verify the part numbers for the Sport Suspension. Remember, I removed or examined them.

Front Spring - 171.321.10.04, 1 Yellow 2 Blue
Rear Spring - 208.324.00.04, 2 Red
Front Strut - 171.320.34.13
Rear Shock - 171.326.10.00

The part number, from a label pasted to the strut, doesn't agree with the Mercedes part diagram, 171.320.12.30:

https://www.mercedespartsdelivered.com/v-2010-mercedes-benz-slk350--base--3-5l-v6-gas/front-suspension--front-suspension

For the comfort suspension, I put a complete new front strut assembly in composed of:

Bilstein Strut - 35.113430
Suplex spring 19355, Mercedes part number 171.321.09.04, 1 White 2 Blue.
New strut mounts

I didn't take apart the old strut, so I didn't have the rubber spring seat. I assembled it without it, and I haven't experienced any problems.

I replaced the rear shock, 171.326.10.00, with the Bilstein shock, 24.113441.

How does the car ride? Well it isn't all that great! The front does ride a bit better, and the extra ground clearance is appreciated. However, the rear rides very rough and skates over rough pavement and makes a lot of noise.

I'm considering changing the rear suspension. The only thing left to do is replace the rear sport spring, 208.324.00.04, for the standard one, 202.324.25.04, 1 White 2 Grey, Suplex 19177. This is a much more difficult job than the front especially without a special spring compressor.

Frankly, I'm thinking of trading this heap in!

:crying:
 

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Registered 05 SLK55 & 06 Kleemann 55K S8
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That is one of the compromises with buying a small sporty car, the ride will be rough. There just isn't enough wheel base and weight to smooth things out. If you want smooth then you need a bigger car or something with no sporting intentions. A Toyota Solara convertible comes to mind. Tires will make the biggest difference in ride. What size and brand tires do you have?
 

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A smaller wheel with a higher tire sidewall would likely have yielded more improvement.

Also note that the sport suspension goes beyond springs and struts, the sway bars and some bushings are also different.
 

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Super Moderator CA 2012 SLK55 AMG w/P30
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With the jumpiness, did you consider lowering the tire air pressure? Makes a big difference. Check the specs on the inside of the fuel filler door. There are variations available depending on how you drive (your speed).
 

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Super Moderator CA 2012 SLK55 AMG w/P30
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In regards to tire pressure, this is on my door and what Im referring to. There is a wide range to consider. I went from highest recommended to lowest and it made a (moderate) difference in ride.

 

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Discussion Starter #6
Sport to Comfort Saga Continues!

So the other day I took a peek at the rear suspension on my '10 350 Sport. Laying on my back with my Schwaben LED Telescopic Magnet, a great tool, I peered up at the coil spring. I was dismayed to see that adjacent coils had a very small gap. What this meant is that the rear suspension has very little travel over bumps. Essentially, when the spring is compressed, it bottoms out very quickly soaking up very little of the bump.

So I have decided to put in the comfort spring or 202.324.25.04, 1W2Gray. Suplex makes a replacement for this spring, 19177. I ordered them on Amazon for less than a hundred bucks. They won't be here until the end of August. They are coming from across the pond from the Land of Broken Springs.

At that time, I'll make a comparison of the two, essentially counting coils and making measurements of pertinent factors.

:surprise:
 

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Registered 05 SLK55 & 06 Kleemann 55K S8
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The shock bottoms out before the springs bind, that is why they have bump stops on them.
 

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Discussion Starter #8
The shock bottoms out before the springs bind, that is why they have bump stops on them.
I didn't say anything about the spring binding or the shock bottoming out. What I said was the spring doesn't have enough travel to soak up the bump. What limits its movement, bottoming out, is a bump stop either external to the spring or built into the shock.
 

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Discussion Starter #9
BTW, I doubt the bump stop built into the shock is strong enough for the job. I believe the rear bump stop is external, but I'll find out when I install the new springs.
 

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Registered 05 SLK55 & 06 Kleemann 55K S8
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I was dismayed to see that adjacent coils had a very small gap. What this meant is that the rear suspension has very little travel over bumps. Essentially, when the spring is compressed, it bottoms out very quickly soaking up very little of the bump.
The gap between the coils has nothing to do with it and the spring does not bottom out, the shock does. Bump stops have been used for a long time, this is nothing new. By the time a shock would get compressed that far there is not very much force left as it has been absorbed.
 

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Registered 05 SLK55 & 06 Kleemann 55K S8
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Actually now that I think about it more, I think the limitation is likely built in to the multilink mainly. Any idea if your suspension has been redone recently? If so, were the bushings tightened while under load? If not they will be much stiffer. That could definitely be your problem.
 

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Discussion Starter #12
Actually now that I think about it more, I think the limitation is likely built in to the multilink mainly. Any idea if your suspension has been redone recently? If so, were the bushings tightened while under load? If not they will be much stiffer. That could definitely be your problem.
I bought the car new. The rear suspension has never been touched. I don't have a problem; the car does!:laugh:
 

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Registered 05 SLK55 & 06 Kleemann 55K S8
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I bought the car new. The rear suspension has never been touched. I don't have a problem; the car does!:laugh:
So you changed the rear shocks without loosening any bushings? And why did you put performance shocks and struts in? B6 is the same that comes on the sport package, you wanted B4's I believe.
 

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Discussion Starter #14
The gap between the coils has nothing to do with it and the spring does not bottom out, the shock does. Bump stops have been used for a long time, this is nothing new. By the time a shock would get compressed that far there is not very much force left as it has been absorbed.
When the car is sitting at rest, the gap between the springs gives and indication of just how much the springs can be compressed or their travel on "bound"

Springs can and do bottom out. Bottoming out means the spring has reached the limit of its downward travel whether that travel is limited by bump stops or not. Again, I doubt the bump stops in the Bilstein shocks are sufficient to control the travel of the spring. I'm fairly sure the bump stops are external.

Another observation come from measuring the travel in a rear shock. I have one in front of me, and I'm pretty sure it has more travel than the spring.

A bump applies a force to the spring over a distance or compressing the spring. Force X Distance = Work or Energy. This energy is stored in the spring and is released when the spring return to its uncompressed shape.

The comfort spring probably will be softer or lower rate allowing more compliance over bumps. This will allow it to absorb more energy from a bump and allow a more comfortable ride.
 

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Discussion Starter #15
So you changed the rear shocks without loosening any bushings? And why did you put performance shocks and struts in? B6 is the same that comes on the sport package, you wanted B4's I believe.
I wrote to Bilstein technical Department. The B4s are OEM, They recommended the B6s as a replacement for both the stock & sport suspension. Essentially they are just a better grade of the B4s. They also have a lifetime guarantee.

What bushings are you talking about? The lower end of the shock is held in place by a bolt going through the wishbone and into a metal sleeve in the shock. The sleeve is surrounded by some sort of hard rubber(?) material. The bolt comes out of the sleeve through the wishbone held in place by a nut torqued to specifications. No bushings were molested in this installation!:laugh:

Anyway, none of this is important. I know how the rear rode before I installed the new shocks. The shocks didn't change anything.

Mercedes has two shock and spring pairs, one for sport the other for comfort.
 

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Registered 05 SLK55 & 06 Kleemann 55K S8
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When the car is sitting at rest, the gap between the springs gives and indication of just how much the springs can be compressed or their travel on "bound"

Springs can and do bottom out. Bottoming out means the spring has reached the limit of its downward travel whether that travel is limited by bump stops or not. Again, I doubt the bump stops in the Bilstein shocks are sufficient to control the travel of the spring. I'm fairly sure the bump stops are external.

Another observation come from measuring the travel in a rear shock. I have on in front of me, and I'm pretty sure it has more travel than the spring.

A bump applies a force to the spring over a distance or compressing the spring. Force X Distance = Work or Energy. This energy is stored in the spring and is released when the spring return to its uncompressed shape.

The comfort spring probably will be softer or lower rate allowing more compliance over bumps. This will allow it to absorb more energy from a bump and allow a more comfortable ride.
I am fully aware of how a suspension works. I used to race semi-pro and set up my own suspension. I have fully adjustable KW V3's on my car.

No, a suspension should never be designed for the spring to bottom out, you are just asking for broken springs. That is the whole point of a bump stop and I have never seen a somewhat modern car without them.

You are missing a huge factor in your brief description of how the suspension works, the shock. The shock will make a MUCH bigger difference in ride than the spring will and you put the same shocks in you had before. It is no surprise the ride did not change much as the shock's resistance to movement plays a much large role in the ride quality than the spring. The shock/strut limits how fast the spring will compress and return to the normal length (the fluid inside goes through an orifice) . A stiffer shock will not allow the spring to compress as fast, so you feel the bump more. If you put the B4 shocks in then you would get to use more of the suspension travel as the shock will allow the spring to move more. The shock/strut and tire sidewall height are the biggest factors to ride quality.

If you wanted a softer ride you should have went to softer shocks and smaller wheel diameters.
 

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This thread is now closed for discussion and any 'offending' comments have been removed.
 

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Discussion Starter #18
An Update of Sport to Comfort Suspension

I made a minor error in my post, so this is an update to correct my mistake. Rather than repeat what has already been said, I'll put it in a straight forward listing of parts.

Front W/Sport

Spring 171.321.10.04 - 2B1Y
Suplex 19356
Strut/Shock 171.320.12.30

Rear W/Sport

Spring 202.324.25.04 - 2G1W
Suplex 19177
Shock 171.326.10.00

The following is the object of this post.

Front W/O Sport

Spring 171.321.09.04 - 2B1W
Suplex 19355
Strut/Shock Bilstein 35.113430

Rear W/O Sport

Spring 208.324.00.04 - 2R
Suplex 19038
Shock Bilstein 24.113441

I used all new parts, since I found attractive discounts on them. BTW if anyone wants to buy my Sports Package parts:

https://dayton.craigslist.org/pts/d/miamisburg-mercedes-benz-slk350-parts/7006758969.html

0:)
 

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Super Moderator CA 2012 SLK55 AMG w/P30
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@Wild Bill Should we delete the original thread/post then? OR attach this post to that thread for continuity?
 

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Discussion Starter #20
Probably best to attach it, since the original contains some information necessary for continuity.
 
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