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Discussion Starter #1
To start with, I am not necessarily looking for a sportier ride, nor am I planning on tracking my car. But, I am finally starting down the road of trying to work out the suspension on my ’02 SLK320 I bought back in February and could use some input on trying to resolve a little suspension issue.

The car obviously has some problems with the suspension. There is a harsh bouncing, or hopping motion that seems to be coming from the rear of the car during regular everyday driving. It reminds me of the ride one would get on a horse & buggy, or older spring-leaf suspension car if a leaf was broken.

My mechanic has commented that it is the worst riding SLK he has ever been in and it is described as harsh, not rough or any term one would associate with a sport suspension or similar. We have found no damage or problems when we have visibly inspected the car and I know it isn’t supposed to be this way. (I have had cars with true sports, or race suspension and this is not that sort of thing.)

Anyway, the only thing that we can determine is that the car has had aftermarket shocks added to what look like the OEM springs. The car has 80k miles on it and the shocks look to be fairly new (within last 10k miles), we assume the springs are original.

My mechanic seems to blame the shocks; I am more inclined to think it is old springs in conjunction with new shocks. Neither of us are suspension experts. he would have me replace everything with OE parts, shocks and springs.

I do not have tons of money to toss at this car, but am trying to decide if I should gut the whole thing and get something like the H&R Cup Kit (with springs and shocks), or look into a process of elimination, starting with new springs either OE or after market and then attack the shocks. (My mechanic would have me start with shocks)…

I can get a cup kit with everything for about $650, plus about $200 for the install. New OE springs would run me a little over $200, and all new OE shocks about $450, so its a wash whether I go after-market or OE.

The install of either, since nearly the same amount of labor is involve would be $200 either way, but if I found it wasn’t the springs and needed shocks, I would end up having to do another $200 for visiting the shop twice. If I didn't do everything at once, so I am probably looking at $850 or so for the whole thing, which brings me near Coil-over territory which introduces some adjustability options not available with the lessor kits or OE.

My issue is I am not overly familiar with these cars to know if there are more elements that could be at play and whether or not going one route, versus the other would open up additional problems. With 80k miles on the clock, I recognize that things wear out and will need to be replaced. I do not want to prematurely awaken another problem by trying to fix another, no matter how-likely it be eventually I will have to address those parts as well; i.e. bushings etc.

Any other SLK owners have similar issues at 80K plus miles to be able to help me determine if it is the old springs, or something else. Am I overlooking something simpler that one might be able to suggest as well? Any direction before I start throwing money at things would be helpful.
 

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i am on the same boat looking to replace shocks for 02 slk320 too. The cheapest OE shocks i finds are Sachs OE at PCPeuro for about a bit less than $300 shipped. Money is tight that is why i am debating on either those OE or the Bilstein HD for around $420.
 

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New socks

Ou have a 10+ year old car, not sure how many miles, but it's a safe bet you need new shocks. Springs? Well for 200 why not? Metal fatigues and its very possible the steel springs are fatigued
 

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10yrs isn't really that long... I'd tend to go with your mechanic...and those above...it's most likely the shocks.

The car is fairly light, and probably driven on relatively smooth roads (in comparison to a 4W drive for example)...so it's less likely that it's the springs. Is it riding at the right height? (wondering if the springs are fatigued (unlikely) or perhaps have been cut to lower the car)
 

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Discussion Starter #6
The only reason I am hesitant to just throw shocks on the car is that the previous owner did that... there is a set of KYB's on the car that appear to be fairly new (within 10k miles). Thus my inquiries... if there is another problem, then throwing $500 worth of new shocks at the car will not resolve it. The problem seems to be worse when there is less weight on the rear, i.e. when fuel level is lower, or top is up, vs down.
 

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The ride quality problem IS the KYB shocks. If you search under my name, you'll find a rant that I wrote a few months ago on this topic. At this moment, I have a pair of KYB shocks sitting in my garage that have 100 miles on them.

I had replaced the rear OEM shocks on my '01 320, in pursuit of an improved ride. I was sorely, and painfully disappointed by the harsh, unforgiving, buckboard qualities of the KYB product. I re-installed the OEM's and decided to perhaps try the Koni product someday. (I've had good experiences with Koni products in my Audi).

The upshot is, the the springs are likely to be fine in your car, but the shocks make a world of difference in the short-travel, short-wheelbase world of R170's.

Best wishes.
 

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In general - coil springs easily hold within their original spring rate - way past 200K miles. The exceptions are coil springs which have been severely over-loaded and thus drastically compressed for months.

I have pulled original coil springs out of many 20, 30, 40 year old cars - and had their spring rates accurately measured. 90% of the time they check out within factory spec.'s

Ride quality is effected when the original springs aren't matched with shocks that meet OEM Spec.'s. On the other hand, most major shock manufacturers do sell shocks that meet OEM spec.'s. There are always exceptions and screw-up's... but I am surprised to hear "GaryMedia" had such a bad experience with KYB's -but it is good to know.

Ride quality is most directly effected by tire selection and air pressure. So the first thing to look closely at are your tires. With bad shocks - you should see evidence of "cupping" usually on the inner and outter edges of the tires. This is caused by the tire bouncing up/down on the road - because the shock isn't "damping" the action/re-action between the springs and tires. So the tire spins and hits the road, then bounces up and spins, then gets pushed back down spinning and hits the road again. What do your tires look like?

Also the age of the tires matters as well - older tires get harder with age. With 50 series sidewalls or less - you will really notice this effect.

The second most common cause of harsh ride - are worn suspension bushings that are allowing the shock taken from the road - by the suspension - to be transmitted into the body. Your comment about the rear of the car "hopping" would lead me to look closely at any/all suspension bushings and/or the proper torque of all fasteners. The smallest amount of free play caused by worn bushings or loose fasteners - in the attachment points - where the suspension components are attached to the body - will allow the transmission of much higher levels of shock from the suspension into the body {E=MC squared} or dynamic torque vs static torque ie get something moving even slightly and you have a lot more force.

FWIW,
Carl B.
 

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The ride quality problem IS the KYB shocks. If you search under my name, you'll find a rant that I wrote a few months ago on this topic. At this moment, I have a pair of KYB shocks sitting in my garage that have 100 miles on them.

I had replaced the rear OEM shocks on my '01 320, in pursuit of an improved ride. I was sorely, and painfully disappointed by the harsh, unforgiving, buckboard qualities of the KYB product. I re-installed the OEM's and decided to perhaps try the Koni product someday. (I've had good experiences with Koni products in my Audi).

The upshot is, the the springs are likely to be fine in your car, but the shocks make a world of difference in the short-travel, short-wheelbase world of R170's.

Best wishes.
I agree, my favorite combination on the slk320/crossfire platform are koni shocks with eibach springs. In my personal opinion it was an excellent blend between excellent handling and comfort
 

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The only reason I am hesitant to just throw shocks on the car is that the previous owner did that... there is a set of KYB's on the car that appear to be fairly new (within 10k miles). Thus my inquiries... if there is another problem, then throwing $500 worth of new shocks at the car will not resolve it. The problem seems to be worse when there is less weight on the rear, i.e. when fuel level is lower, or top is up, vs down.


That may very well be your answer. I tried a set of KYB's on my 300E once and it was like mounting solid steel rods in place of the shock absorbers. The ones for the SLK might not be so stiff, but if it were my car I would want to get them off of there and replace them with some Bilsteins or another quality shock.

Honestly, I don't understand your hesitancy for just putting shocks on the car first. Even if you do other things, you'll have the shocks in place and ready to move to the next step.

I have driven lots of cars to high mileage and maintained cars for others that were driven to high mileage. As much as 500,000 miles. I've never replaced springs for any other reason than to change spring rates. They really don't normally wear out.

Best of luck with it.

Doc
 

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...most major shock manufacturers do sell shocks that meet OEM spec.'s. There are always exceptions and screw-up's... but I am surprised to hear "GaryMedia" had such a bad experience with KYB's -but it is good to know.

Ride quality is most directly effected by tire selection and air pressure. So the first thing to look closely at are your tires. With bad shocks - you should see evidence of "cupping" usually on the inner and outter edges of the tires. This is caused by the tire bouncing up/down on the road - because the shock isn't "damping" the action/re-action between the springs and tires. So the tire spins and hits the road, then bounces up and spins, then gets pushed back down spinning and hits the road again. What do your tires look like?

Also the age of the tires matters as well - older tires get harder with age. With 50 series sidewalls or less - you will really notice this effect.

... will allow the transmission of much higher levels of shock from the suspension into the body {E=MC squared} or dynamic torque vs static torque ie get something moving even slightly and you have a lot more force.

FWIW,
Carl B.
Carl,
Thanks for an excellent discourse on suspension, especially with the hint how to spot a problem.
Trouble with some "tuners" is that since old shocks are soft, so they think that new shocks should be hard, and the harder the better. Of course, any mechanical performance analyst will tell you that it should be critically damped, and not over-damped. Old shocks fail to "damp" the resonance, and so the car will bounce up and down (classic test), which is underdamped. Critical damping is where the car overshoots once, and does not pass the equilibrium point on the recovery, and this is optimal. Of course, it's not that simple, with different rebound rates, etc, but it's good to have a starting point for understanding.

I used to have a favourite hill with a irregular tarmac/pavement where I could put loads of torque; when the shocks/dampers were past their best, the bouncing would be emphasised and obvious, even at relatively low speeds.

I must admit, I knew suspension could be complicated, and is sometimes thought of as rocket science, but I've never considered it atomic science! :) (Inertia = 1/2 mv squared, perhaps?)

And as for old tyres; who has old rubber on the rear axle of an SLK? :dunno::D
 

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This might be a good time to recommend some EXCELLENT reading on the subject. There is a book that has been in print many years that does an excellent job of explaining handling and suspension theory. I believe that it is published by HP Books. The title is: "How to make your Car Handle." It's a great read.

Hope some of you find it useful.
 

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At 66,523 miles I just replaced the front Springs and Shocks on my 2003 SLK 230. Dealer said rear suspension is fine.

I bought the parts myself and the dealer installed them for $306.00. THey billed 2.5 hours of labor at $130 an hour with 10% off the labor due to the number of problems I have had over the last 4 months. Spent 4k in repairs this year alone just replacing general things like tires, brakes, hoses, etc...

There is a bump on the highway on my way home from work that makes my tires hit the inside of my car. After replacing shocks and springs, my tires no longer make contact with the car.
 

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Discussion Starter #14
I thought I would resurrect an old thread.... I still have yet to address my original issue, although I did toss a set of new, cheapo Chinese made tires at the rear of the car and the ride quality improved some leading me to believe that was part of the problem. Although I did upgrade the OE 17" wheel to an 18" off of an SL55, so I am running staggered 17 Fr/ 18Rr.


I have purchased all new rear suspension parts with new bushings which I want to have installed at the same time I remove and replace the KYB's. My dilemma now is spend roughly $560 on new OEM shocks and OEM springs, $680 on new Bilstien shocks and H&R springs, or $708 on an H&R cup kit (coil overs).


Having lived with this car for almost two years, it is mostly a commuter car (top-up) and a weekend cruising car (top-down), so I almost am thinking of going back to stock, but am expecting a hefty bill from my mechanic to do all the work anyway, so want to do as much of it at once as I can to avoid having to come back.


From what I have read, the OEM springs are probably fine and don't necessarily need to be replaced, but I am thinking the rubber spring perches will, so if the springs have to come out for that I might as well replace them. The car has 97500 miles on it today....


At this point the OEM springs are more expensive than a set of aftermarket ones through various sources, oem shocks are only marginally cheaper than bilstein... but since I have never driven this car and seen how smooth the ride was or wasn't stock. I am left wondering what the stock ride might be like and if it would be so smooth I might be happy with it, versus the sportier ride I would get from the upgraded aftermarket stuff.


Thoughts on this two year old thread and posters.
 

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I'll give you all the suspension theory you'll ever need. If your car goes thumpy bumpy down the road, you need new shocks. Shocks control the oscillations of the springs on bound and rebound. When you replace the shocks, make sure the connection at both ends of them are in good shape.

Use a good quality part like Bilstein. Springs never need to be replaced. If you want to preserve the quality of your ride, don't install lowering springs. A short spring has less travel on bound and rebound and will be stiffer, higher rate, to control bottoming out. It will also require a shock to match the higher rate.
 

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Discussion Starter #16
Hey any and all input is appreciated... this is good info and will be taken to heart. The remaining question though, if springs aren't really an item that would need replacing. What about the rubber perch/pads...if replacing all the other rubber parts; i.e. bushings, etc. Should they be addressed, the parts themselves are cheap, but I know my mechanic would probably charge me the same to replace the pads, as he would the whole spring.


As of now, I have standing ready all new 4-link parts with new bushings, diff mounts and bushings, etc for the rear and was planning on tackling it first then moving and do the front, including steering end links. Ultimately I want to get a smooth ride, if not finally learn what an SLK is suppose to ride like.
 

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Did you ever get your ride sorted out? I was curious if you had installed all of your bushing kit parts yet and if that made a difference. Also, are they OEM style/quality or sportier polyurethane or similar? And where did you get them from?

Ride quality is usually either for comfort or for sport handling...unless you go real high dollar to get the best of both worlds. Springs can certainly deteriorate over time. The constant weight of the car and changes from hot to cold and such will affect them...but over a long period of time from my experience. The most common thing i have seen is they will settle, and by that i mean compress permanently a little bit. Bad struts will leave you bouncing on the springs, which is truly awful and I have had happen on a car before. My 02 slk230 still had original springs/shocks, and the shocks were pretty decent considering the age and now over 150k miles, but I know they weren't as good as they once were. My father bought the car new (and I bought it from him a few years ago), but it had been so long ago, I can't really remember what it originally felt like. That and many other factors play into ride than springs and shocks too...like the bushing kit you bought, which is why i was curious as to how that worked for you. I have not yet looked at spring options for the car, but I will. I can't help but wonder what switching to a coil over setup does to handling/ride as the car was not designed for it. It may be fine, but it would be for sure a point of consideration for me that I would have to research. I think it could end up being very different feeling. They also make progressive coil springs, which you should look up some pictures of if you are unfamiliar. Part of the spring is softer and more closely/tightly coiled, while the other part is more firm and the coil is spaced further apart. This is supposed to give you reasonable comfort for daily driving, but when you corner hard, the soft part compresses fully and then you are riding on the more firm portion of the spring for better handling. I installed a set on my old mini cooper, and I loved them. They were Tein S-tech i believe, and were green. Its something else to consider if they are available for the SLK.

I just installed a set of the KYB gas adjust shocks, and wanted to throw in my 2 cents. I know they will not ride as comfortable as OEM, and they are not marked that way. They are supposed to be a performance upgrade, and I think they are. Keep in mind it has been a long time since i drove the car in new condition, but I am overall happy with them. The turn-in responsiveness is really good and noticeably improved, which is their main marketing claim. If you are not familiar with the terms, this means that if I turn to the right, the car turns quickly without compressing the front left as much. It just turns. At a high enough speed with a hard enough turn, it still will, just not as much as stock. I am extremely happy with this and I have been hammering turns every chance I get because it is a lot of fun now. I do not remember the car being this responsive new, and it felt a bit more spongy. Ride quality seems somewhat reduced, but it is not horrible. It is slightly bumpy at times, but still quiet and smooth. It has a slight and firm bouncy quality to it, which I do not remember it having new/stock. I feel like I am using the word "slight/ly" a lot, and that is because, compared to other cars I have setup to be sporty, the loss in comfort is minimal on my SLK. I have to attribute some of the diminished ride quality to other aging suspension components, but it is not as pleasant as stock in that regard. If you have ever had a car that handles extremely well, you know it could never ride like a S-class.

Suspension has improved dramatically over the last 13 years, and even big 3 ton SUVs like a Range Rover Sport (which I owned recently) can handle like a car and turn in so well it is amazing. I feel like some people forget this in their analysis, but make no mistake, the newer SLKs will feel very different than a 2002 did new. You really can get the best of both worlds these days, but those parts also cost a lot more. Those magnetic damper systems are pretty impressive if you have ever driven or ridden in a car with it.

If you do not want to compromise comfort, go OEM/style all the way. If you have the funds, you can look into a fully electronic adjustable damper system so you can have both (assuming its available for the SLK). I have seen those kits for other cars around the 12-1500 price point. They let you dial it in and find your perfect sweet spot, which is very cool. But performance upgrades will pretty much always sacrifice some comfort for cornering ability...you have to to transfer weight faster. Unless you have rattles, the shocks probably are the biggest factor in ride. Wheels/tires can make a very big difference too if they are not stock. Even among the same size low profile tires, there can be a big difference. Run flats ride like garbage and are hard so they don't grab as well. Just something else to consider. Reading reviews is crucial for me when buying tires.

I also would recommend doing the install yourself if you can and have the tools. It is not that difficult to do, and you will get a better understanding of how it all works when you are in there looking around and doing the swap. Plus it saves you money on the labor.
 

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Random thought on the crunchy KYB's... what if they weren't correctly ordered... if they were for a lowered setup they might not have enough stroke for the stock suspension travel and you might have been feeling the internals hitting the end of their travel.
 

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This is a great thread! Wondering about what to do on my 50K mile SLK320 6-speed suspension. Original OEM. Has anyone tried the Bilstein B12 spring/shock set-up? Pricey at $725 + installation. I definitely do NOT want a pogo stick track car ride but crisp handling would be nice. Love the car. Stock wheels with Michelin Pilot Sports.
 

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Update. 65K on the SLK320 and took to a Hagerty track day. There was a bit of hopping around at speed but it could be “driver error”. Still looking for a little crisper handling but not track car harsh. Michelin Pilot Sports amazing on this car.
 
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