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Registered 2006 SLK350
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472 Posts
Discussion Starter #1
Hi guys!

As part of an effort to improve the handling on my 171 I ordered up AMG sway bars and plan to install them tomorrow. Reading through WIS seems to indicate you need to drop the rear end a bit to get the rear one out - I expected that. But on the front one WIS says you also need to drop the front cradle.

Is that really required on the front? Sounds like it's quite the job and that it would require another alignment....this causes me to wonder if anyone has R&R'ed the sway bars on your car and was all that really necessary?
 

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Registered 2006 SLK350
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472 Posts
Discussion Starter #2
Since no-one replied, and the job is done, I'll finish up this thread. I replaced the front and the rear bars and it required dropping the rear end and dropping the front engine cradle. We got it done in record time because I did it at a shop and paid one of the mechanics to help me out. This is not a job that the home mechanic can do very easily. I think the book time on the rear alone was 5.5 hours. We banged out both in 4 - but with a full shop at our disposal.
 

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Registered 2006 SLK350
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472 Posts
Discussion Starter #3
Hi Folks!

My R171 had a great deal of body roll at speed in corners especially when there are dips in the corner. Literally unsafe at speed of 140 KPH or so through sweepers that dipped or rose up mid corner. The chassis would go one way, the body another. This was also noticeable to oncoming traffic. They would see it and think you were out of control even though you weren't.

I was torn between struts and sway bars. The car has 120k on it and the struts are original. My model does not have the sport suspension, which, in my opinion, is a good thing. Nevertheless, handling in corners at speed was, effectively, a waterbed.

After some thought I ordered in the AMG sway bars from Mercedes for the car. These are the stock bars for an AMG55. They came from Germany, they were marked Eibach, and we put them in keeping our fingers crossed. The front was 5mm thicker than the OE bar and the rear was something on the order of 1.25 mm thicker. In both cases, they were much heavier.

Installing them was fairly involved. I had access to a shop and also paid one of the mechanics to help me do it. I cannot see anyone doing it at home. You have to drop the rear diff and suspension and then pull out the existing bar out one side and then install the new bar and button it up. With the front, you have to drop the engine cradle. So you really want to have an engine support fixture sitting on top of the engine compartment holding the engine up......

The book time on the rear alone is 5.5 hours. We banged out front and rear in 4. Bear in mind, this is in a fully equipped shop and I paid a mechanic to help me with it. There were no problems with fit other then that the front power steering hose had to be bent slightly. I mean slightly. And then everything had a lot of clearance (alternator, A/C compressor, PS lines). Bear in mind, the stock bars and the AMG bars in the front had two sets of holes in them. You can tighten the bars by drilling out the other hole and using those.........so if you have a car that is almost right, you can try the other holes and tighten the bars.........

The ride is now firmer. It is not harsh. But it is close (probably 80% - any further and you would risk the ride being harsh). In a straight line there is little difference. The goal was to improve handling without sacrificing the ride quality. Manhole covers are actually smoother than before. Speed bumps are firmer. Interestingly enough, when the road has ruts in it, such as coming to a light, it does tend to get sucked one way or the other more than before. Railway tracks are much the same as they were, just a little more solid. So, actual ride performance in Comfort mode is slightly firmer. It did not destroy the ride quality but it is firmer.

OK, so how about performance? I took it down a twisty road that is little used and nailed a few corners. This is a well-known road so I know, very well, how it was before the bars went in. To my utter shock and surprise, the car was flat in ALL the corners. Literally flat. The edge of the tires dig into the corner (the loaded side) like you would not believe. On one corner I hit very hard (a left hand turn) the right side was loaded so much that the left side wanted to lift a bit. But here's the thing, it lifted evenly front to rear. In short, that side of the car lifted as one side.

Today I took it out for a 3 hour run to a road that has some real problems. This is a road that locals hit at +140 KPH in the passing lanes. There is on particular spot on that road that is a corner with a big dip in it. All the locals know of it because at +140 KPH it's dangerous. That's the one I wanted to see how it performed. And it did very well! There was still some rise but it was safe and the rise was very short-lived.

The rest of that road (mountain passes with sharp corners) was taken in 4th gear. This is what I learned that is very important. With A mode, and the trans manually put in 4th (automatic) it's perfect for that road. You get roughly 165 KPH to 170 in the top of fourth. But with A mode, you can hold it at the red line in 4th without it arbitrarily going into 5th. The auto trans in these cars can drop two gears at once. This means if you set the limit at 4th, it can go straight to second......

What that means is that you can be flying into a corner in 4th, doing 165, nail the brakes pre-corner, and...if it's a sharp one, the trans will drop to 2nd. So your corner exit is in the fat of the power band and you come flying out of the corner like you know what you are doing. The sway bars keep it flat and you can concentrate on only three things, brake, steering and throttle. You can ignore the transmission altogether. So I learned something very important, when nailing twisties, assuming the suspension is good for it (it now is) you must limit the top gears.

The car actually does have a power band. On many of the straights, on exit, I was keeping the engine revs in 4th at around the red line. A mode allows you to dance all around the red line without it arbitrarily jumping into 5th which you do not want on that road. On top of that, deceleration from red line goes all the way down to ~3,000 RPM or so meaning your set up for the next corner is perfect.

I could not believe how flat the car cornered. It was unreal. The edge of the tires (Michelin Pilot Sport AS/3+) dig in HARD. Bear in mind, I have turned off torque limiting in the corners and under acceleration. I even manged to get it to slip a bit just to see what the limits looked like. The problem is, the roads are not that good as there is salt powder all over them still. But....keeping it locked in 4th (and below) the car absolutely nailed a stretch of about 10km's worth of tight corners with exits that freaked out the oncoming traffic. The car was FLAT. Did I say FLAT ?? I mean, FLAT !

By the time I was done I was grinning and I knew that my cousin, the shop owner, could have driven the same corners with my car and come out saying, "That was fun!". I routinely drive that road on my 600 with a Moto2 engine (sport bike). I have to say, no-one will shame the car now through the corners and if my regular motorcycle troup was with me, I would be in the thick of it. I'm not saying it's now a Porsche or a Ferrari, the car is, ultimately, a Gran Touring car. But it nails the corners flat and will certainly keep up with most all cars and bikes.

My goal was to NOT ruin the ride. The AMG55 bars on my 350 did make it firmer but I would not, by any means, say that the ride is ruined. The thing is, it's now safe in corners at speed. A mode makes a huge difference as does lowering the gear to one which suits the road. The side of the tires dig in. And I mean, DIG in. corner exits are incredible with just the right amount of squat on acceleration.

I am still getting used to it but it has actually turned the car into a sports car. If someone already has the sport suspension, and finds it still has body roll, I would suggest drilling out the front hole in the front sway bar and trying that first. If someone has a car like mine, with stock suspension (no sport) then I would suggest jumping straight into the AMG bars if you can handle a little firmer ride. As mentioned, man hole covers, which used to be problematic, are now much better.

Based on other's reports, I would never put Billstein B6's on the car. It seems that everyone that did ruined the ride. I would go with OE replacement Bilstein B4's however. But looking at it now, I will pass on struts for some time, perhaps forever or until they are shot.

I think I did you guys a BIG solid with this ride report, especially when I see how many people modified their suspension, to the tune of many thousands of dollars, and ruined the ride......
 

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Premium Member 2013 SLK350
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1,072 Posts
@marvin-miller, thanks for the write-up of your sway bar switch and driving experience. That was awesome to read... you wrote it so well even readers felt they were driving the same car with you. That was good writing...

Does anyone know if the option code 486 (Sport Suspension) in R172s with the AMG body kit/package includes the AMG55 sway bars? I know the sport suspension is lower and firmer than the non-sport R172, but not sure if it is harboring the AMG sways. Need someone to confirm one way or another.
 

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Registered 2006 SLK350
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472 Posts
Discussion Starter #5
Thanks for the kind comments!

With the R171 there are 3 different part numbers for sway bars. One for the stock suspension, a different one for the 171's with the 486 option, and different ones all together for the AMG variant.

You won't have the AMG bars unless you have the AMG car. If you look at your front bar you can actually tighten it if you drill out the front hole to the same size as the one that's in use now.
 
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