Here are some tips from having now successfully changed both front springs on a S212 / W212.
Start by watching the available Youtube videos as a first resource but you need the following information to fill in the blanks. [Dont bother with the video where the bloke's young son interrupts him as he wastes time repeating himself whist missing more of the important points than the others. The one that I was just given the link to above is probably the best to start with
Tools:
Spring Compressor. If you can, try to get hold of the type of spring compressor shown in the Youtube video above. It is intended for Merc springs and would make the job much cleaner and easier. They are sold on Amazon and Ebay. The traditional types of standard spring compressors consisting of 2 or 3 individual clamps can be used but you will need a lot of care and may need to use 2 sets (I did). If you don't own a spring compressor buy the right one as you can always sell it on again.
A set of torx bits to help undo the sway arm
Standard socket set. Ideally half inch drive for those for the larger bolts as you will need to give some of the larger bolts some real welly to get them undone. The smallest size sockets you will need for this job are a 10mm and a 11mm
Torque wrench.
If you happen to have use of an impact driver or impact wrench/ air gun this can speed things up but contrary to what some of the Youtube videos say you can do the job without one.
Parts & materials
Suitable spring/s. Ensure you get the right type. If your car has sports suspension you need to ensure you get the right springs. The manufacturer describes sports suspension as 'Standard Avantgarde ' which can confuse many because the word 'standard' sound the opposite of like 'sports' - be assured though that this term standard in that exact context is intended to mean the sports suspension that was fitted as standard to Avantgarde and AMG Sports spec cars.
Brake cleaner or degreasant if you have some
Penetrating oil. I use Plus gas, others have their own preference
Cleaning rags
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Tips.
General: Clean the exposed threads of all the bolts you will be undoing and apply a bit of penetrating oil a couple of mins before you start.
The strut is held to the bub assembly by a large horizontal nut and bolt (different sizes) which is very easy to see plus 2 lower bolts which are accessed from the back of the strut so are not as easy to see. These bolts at the back have 11mm heads. .
The sway bar (it goes by other names) is bolted to a bracket half way up the strut. On one side i managed to unscrew the nut with a socket but the other side was more stubborn and i needed to use a spanner whilst holding the centre with a torx bit. If you need to remove this by rotating the torx bit just remember that you need to turn this the opposite way (as though you were doing it up) nit the same way that you would undo it with the spanner on the nut.
The plastic thing that holds the brake hose and supports the sensor cables needs some explanation. It is held on by a narrow band of plastic that has a very fiddly catch. This needs a small screwdriver to push out the tiny plastic pin. Dont lose the pin but if you do im sure it can be replaced by a small bit of stiff wire. Remember how the things came apart. The rest of it then needs to be rotated to free it up. You cant see it but part of this thing is inside a cavity in the strut. That is what is holding it in place and it needs to be carefully rotated to pull that bit out so it can be moved clear. You may need a medium sized screwdriver to start to prise it to start moving it. Once moving firmly rotate it and and it will come out.
It may help to get someone else to help you lift the strut out of the car. I managed this easily enough though, its not that heavy or that awkward really.
Ive said to try to use a spring compressor that is made for Mercedes springs if you can. I didn't have one but soon realised the set of 3 standard spring clamps I had were not going to be enough so i nipped out to Halfords to buy another set of slightly more substantial ones. Mercedes springs are both long and very tough to compress. Take care not to allow a spring compressor to slip off as the spring can let go with a huge amount of force. Its ok so long as you treat it with respect but I would say never allow a spring to point directly towards you when working on it until the whole thing is bolted safely back in the strut.
The spring has a top end and a bottom end. They are often not marked and the difference is far from obvious to see. If in doubt rest the spring on a bench or flat surface: one way up it will balance but turn it over it will either sit at quite a mad angle or will just fall over. The end that sits straight is the top of the spring. No one points this out. If you get it wrong the spring will never sit right in the strut and the top plate will be as wonky as a politician's promise.
Refitting is the reverse of removal as they say in all the best manuals. And probably some of the worst ones too.
The plate at the top of the strut will only fit the car one way. Dont worry if it is not in the right place. Bolt the bottom of the strut to the hub then put a socket and ratchet on the large centre bolt at the top of the strut and just rotate the top plate until all 3 screw holes line up so you can fit the 10mm bolts.
Ive heard different versions for the bolt torque settings but the consensus seems to be. The 3x10mm top nuts (under the bonnet) about 35nm. The sway bar bolt about 50 to 60Nm. The main sideways nut and bolt 100Nm but only tighten this up when the strus is under compression - put a trolley jack under the asembly and lift about half way up it's length of travel. The two lower hub to strut bolts 70Mn, undo them again then tighten to 100Nm. The top bolt 100Nm. Check these settings yourslef independently with the main dealer though as Ive collected that information from different sources so would not claim it is accurate.
Allow plenty of time.
