Many have no idea where to find the power steering reservoir on the M120. It is genuinely hidden in plain sight! Also questions that pops up are which fluid do you use for the Mercedes W140? I will answer both.
Open the hood and look down on the engine. Then take your finger and point to the first star emblem you can see.
The star is part of a plastic lid. Remove this, it is held in front by two tabs and then you slide it towards you.
Now point at the container with the cap on it. Congratulations you have found the power steering reservoir.
Open the cap and measure the . I am pretty sure the level will be low. This has to be the most neglected fluid on cars. This is the main reason the steering box gets sloppy, due to the fluid running low, wrong type of fluid and just pure neglect.
The fluid you should use is Febi Lenkgetriebeöl 08972 or an oil with MB 263.3 approval. Alternatively you can get it directly from Mercedes. Do not use ATF for the love of God. AFT works, but will wear the steering box prematurely.
This will be a short one. Easy job, anyone could do it!
Almost forgot to mention: There is a CATCH, that might get you stuck! Better read on then.
Get some new struts. Prepare your tools. You should have a hammer and a couple of drive punches also in addition to the normal socket tools and a set of spanners. This job is fairly easy and anyone who can change their own wheels are able to do this job if you are prepared.
Start by taking the rear wheels off. I recommend putting the rear on jack stands while you work on the rear end. There will probably be a lot of banging with the hammer, but you will probably no be moving under the rear end. Now you can locate the lower bolts, spray them with rust penetration so it will be easier to loosen the bolts. They are probably a bit crusty from rust. It is also a good time to inspect other suspension components such as the rear sway bar bushings and the brakes. Make note of worn components and order them for a fix later.
While the rust penetration fluid is working, start by locating the upper damper mounts in the rear trunk. The left side is located below the first aid kit area. Open the lid, remove the first aid kit and the warning triangle, then locate the foam and remove it to find the upper strut mount.
Make note of how the bushings and supporting plates are mounted. Support the lower control arm with a jack, because the spring will push out the arm once the damper is loosened. When the strut mount is found. Use a spanner along with an adjustable wrench to keep the shaft from spinning when loosening the upper nut.
Now that the top of the strut is loose. You can move to the lower bolt. This is a bit more tricky if it is stuck. Use two sockets or a socket in combination with spanner. You might need some force to loosen this nut because of rust.
When the nut is removed, the tricky part starts. You will need to drive out the lower strut bolt. Is is probably rusted and needs a good pounding with your hammer. Hammertime!
No pictures of that process here since I got so frustrated I forgot to take any. Anyhow when the strut is out you can mount in the new strut. If you completely break the bolt you will need to get a new one, since most of the dampers do not come with new lower bolt and nut. Be sure it has enough strength and do not simply get one from the hardware store without checking the steel rating. The nut used must have self locking threads, otherwise you will need to use a locking washer with the nut. Tighten the nut until you feel it is tight.
You might need to use the jack down or up in order to move the control arm in the height so you can get the strut in properly.
Now move up and fit the upper strut bushings and nut. Place the bushing first, then the plate. The new strut can either come with 1 self locking nut or two separate nuts. When tightening the nut you have to make sure the shaft is not turning. Turning the shaft excessively can damage the inner seals of the strut and it might start leaking. Start tightening the nut until you reach the bushing. The rest of the tightening must be done while the car is fully weighted on its suspension.
The same procedure is obviously for the right side. It is located behind the right side compartment, and behind the plastic cover which can be removed.
When tightening the upper strut nut, tighten so the ribber bushing is a bit squeezed and you feel a resistance. This is usually enough. If the new strut has two nuts, use the upper one to secure the lower nut. This is not necessary if the damper comes with a self locking nut. Do not reuse the self locking nut front he old strut.
Hope the car will feel a bit more responsive in the rear end!
Changing out worn shocks might be most effective and cheapest fix that can transform the ride handling of your car for the better. My S600 had very noticeable up and down wobbling when driving over bumps and a quite large body roll making in tight corners. It was becoming a bit boat like there at the end. The S600 is a very heavy car and needs good handling when going fast. A flatter ride in corners also makes for a more comfortable drive overall, so your passengers don’t wake up from their naps.
Changing the shocks will reduce wear on other more expensive suspension components like bushings and tires, while overly worn might damage the suspension. Changing the shocks is in your interest to be an economical DIYer.
The front suspension uses normal a McPherson setup with separated gas shocks detached from the springs and can easily be removed. The rear suspension on the other hand uses the more complicated SLS leveling suspension setup and don’t use shocks at all. Instead it uses hydraulic rams along with pressure spheres. More effort and money is needed when doing maintenance on the rear suspension than the front. The SLS however normally lasts a lot longer if you remember to change the fluid once in a while.
When changing the shocks you should also use the opportunity to inspect/change some other wear items easily accessible in the front suspension. This could be sway bar links or the brake rotors and pads. The sway bar links wear down faster than the other suspension components due to their tiny ball joints and should be replaced whenever cracks appear in the sleeves or any slack starts to be noticeable. Worn sway bar links can make annoying sounds for you and your passengers. We all know expensive cars are known for being the most squeaky cars around, let’s change that!
You should expect to use around half day to a day on this job, depending on your skill set, the amount of rusty bolts and your tools at disposal. It’s something you can do easily on a weekend. When doing the job I was even under time pressure since I had to catch a flight the same day. I managed to catch the flight and get the job.
If you want to bundle more front suspension jobs while doing the shocks, I recommend removing the front wheels and inspect the suspension such as the sway bar links, brake pads and rotors as well as the tie rods. Any more advanced jobs than that you will will require a lot more time invested so be sure to plan accordingly. Usually large front end jobs require a re-alignment of the suspension, but is not required here.
Parts needed (as described in the article):
2x front shocks. I recommend premium brands such as Bilstein or Meyle
1x Left front sway bar link
1x Right front sway bar link
I ended up using quite a tool collection because of rusted bolts on the sway bar links, but this might not be the case for you. I think this collection of tools goes into most home car mechanics tool box, but there might be a couple of them you should consider getting. Always better to be prepared than sitting there stuck without finishing the job.
Jack and 2 jack stands
Long breaker bar
A set of long spanners
High quality hex sockets
Pin punch driver
Long Hex keys
Propane blow torch (super handy when things are stuck)
Start by raising the front of the car and remember to use the E-brake together with wheel stops. Place the front on jack stands. I also like to keep the jack in the up position as redundancy on the side I’m working with. You can lift the w140 with the jack on the rubber jacking pad and place the jack stands more towards the center of the car under the sub frame.
The shocks can be removed when the calipers are in place, but to remove the sway bar links, both the calipers and the brake rotors need to be removed to access it. I will first describe how to replace the shocks since it is a much easier job. Then I will describe how to replace the sway bar links.
Start by removing the lower bolt. Use a long breaker bar and a large spanner to break the bolt loose. Then move to a ratchet to get the nut off. Use the jack to lift the lower suspension arm a little bit to relieve some tension in the bolt through the bracket hole. Then use a punch to smack out the bolt with a hammer. Be careful if the bolt catches too much, then try to relieve more pressure before continuing. Most shocks do not come with replacements for the lower bolt and nut, so try keeping these in good shape.
When the bolt is loose, open the hood and locate the top nut. The top part of the damper can look different from each other. You have to keep the strut bar still with a hex socket or flat pliers while using a spanner to unbolt it. There exists a special tool to do this with a socket, but is frankly unnecessary except if you’re addicted to tools. This locking nut always comes with a replacement nut and you should throw away the old one. When the locking nut is off you can easily remove the old damper.
Before installing the new damper, push it completely down a few times to relieve tension. The installation orientation has no influence if the brand does not specify it. Start by installing it with the top part and the top locking nut. When installing the new damper you must take of not letting the damper shaft rotate while turning the locking nut. Keep it secured while fastening the locking nut. This is to reduce the risk of breaking the internal seal of the damper so it will start leaking. The nut does not need to be extremely tight, but do tighten it until you feel it is secure. It is very important to make a re-tight after the car is on the ground. I will remind you of this again shortly.
Now you will probably notice that the new damper is quite shorter than the old one when you took it out. You therefore have to compress the spring by jacking up the lower suspension arm until you can align up the bolt hole. This might be a bit tricky and use a hammer to punch the bolt through since it is nearly impossible to align them up 100%. Again take care of not ruining the threads on the bolt. The lower bolt and nut should be torqued to 80Nm.
Front sway bar links
Now on to the more fun part where you can expect to meet more of a challenge. First you need to turn the wheel you’re working on all the way out to get access on the backside. Start by removing the caliper, it is held by two bolts. You may require some force to break them loose. Prepare some method too hook the calipers up in the spring to relieve tension on the flexible brake hoses. Never let them hang freely. I used long zip ties here and I could just to cut it off when done. But a simple S-shaped hook would have been even easier!
The caliper might be difficult to get off if the brake rotor has a lip on the edge. Use a pry bar or the back side of a hammer to press in the outer brake pad by using the rotor for leverage. Be careful not to damage the pad material. When the caliper is loose, secure it up onto the spring.
When the brake caliper is loosened you can start remove the break disk rotor. It is secured by a tiny hex nut, but you might find this lost or broken. Mine was broken off on the right side, but the left one was fine. Loosen the nut with a hex socket. If the brake rotor is sticking to the hub, try hammering gently on it with a plastic hammer. If it does not pop off, it can be quite frozen due to rust and you’ll need heat to loosen it. Ignite up your blow torch and heat the area just around the hub. This should expand the rotor just enough so it will pop off with a light hammer blow. Over heating the hub might make the hub grease melt and run out, so be careful with the heat.
Now it’s the time to locate the outer sway bar link nut. Cross your fingers for no rust. It is located right under the brake rotor. The locking mechanism is not the best engineering, since you’ll need either a special tool or trying to combine a socket with some magic tricks. I used a socket, secured it with locking pliers and then used a hex key sticking through it. After some fiddling I managed to get the nut off. You can usually loosen the bolt the first few turns by using just the socket normally.
The upper nut should be the easier of the two to get off, since the lower one usually gets all the rust and is easier to round off the hex bolt head. Soak it thoroughly with rust penetration fluid and let it work for 15 minutes. Then use a hammer and whack that nut good a couple of times.
I got lucky with one side, but the other side I had to drive in an over sized XZN socket with a hammer so it’s surely stuck in there. Then I could get enough torque to loosen the rusted nut. This will obviously destroy the part, but it’s thrown out anyway. Unfortunately I did not get any pictures of this process since I was struggling a bit and running out of time.
Now you should be able to remove the sway bar link. Go fetch the one that fits depending on the side you are working (hopefully you order the correct ones). Fit the top side first, then you move on to the lower side. It can a be a bit tricky to fit the lower side onto the sway bar again. Get a long bar or a long spanner and wedge it between the spring to get leverage to push down on the sway bar.
It is not necessary to tighten the sway bar links very hard, just snug with enough force so they sit on. Remember these will probably rust tight faster than you can say cheese and the hex bolts will round off again.
Caution: Before assembling the rotors, make sure you brush off any old rust off the hub face and the inside of the rotor. This is to prevent rumbling while braking and that the rotor sits on straight! You can use a steel brush and a rough pad to do this. Also brush off any surface rust on the front side of the rotor where it meets the wheel.
The front caliper bolts need a layer of blue thread locker on them since there are no shims or similar. Use 115Nm torque when tightening the caliper bolts.
It can be a bit tricky to mount the wheel if the little rotor locking nut is missing, so a replacement might come in handy here. Otherwise you have to align the hub with the rotor first and then with the wheel when sticking in the bolts.
Now I hope you will take on this task without paying stupid amounts of hours for mechanics to figure this out at a workshop. Go do it yourself!
When your car steering starts to feel floaty and maybe the car is starting to drift to one side so you constantly have to correct when going down a straight road, consider changing the steering linkage components and do a wheel alignment.
I will describe how you replace the tie rods, the center drag link and the steering damper only. I will not describe how to do a wheel alignment, because professional wheel alignment equipment is needed.
Changing the idler arm bushing is also possible if you experience a knocking sound going over bumps, but this procedure will be described later in a separate article.
Get the parts needed for this job, they are quite cheap since they are normal wear items on a car.
Parts you should get:
Right and left side tie rods
Center drag link
Idler arm bushing (job not described in this article)
You will need a special tool for removing the tie rod ends, this can be picked up quite cheap. Either a tie rod fork or a tie rod press tool will do, the latter will not render the tie rod bushing seal useless, but if you are only changing the parts then this does not matter. Additionally you will need a hammer, a torque wrench, some hex tools and some spanners.
Start by raising the front of the car on to jack stands, make sure you block the rear wheels. You will have to be able to remove the front wheels to gain access to the tie rods and also be able to turn the wheels.
Because you are working around the brake rotor, it is important that you wear a dust mask and get a bucket of soapy water and start cleaning the brake rotor and the area around to get rid of all the harmful brake dust before you do any other further work. Think of your health!
When you have cleaned the brake dust, turn the steering wheel all the way left if you are working on the right side, and vica versa.
Get a small pick and clean road grime from the top of the tie rod so you can get a hex tool inserted in to the top. You will loose the bolt with a spanner, but because the whole tie rod end will rotate you have to counter it with the hex tool. When he bolt is off you will notice the tie rod is still extremely stuck. Hit the side hard a couple of times with a hammer to knock the rusted component loose, this might help to loosen it. Insert the tie rod press remove tool and start tightening until the tie rod pops off, this can sometimes be violent. Be careful and don’t lie under it when this happens, because it can happen quite suddenly and the tool and parts might fall on top of you, ouch!
You have to repeat the process twice on each tie rod for both of the car’s sides.
When you have gotten both off, measure the length by counting the turns the tie rod end can rotate before it comes off, it is important that this is exactly the same for the new tie rod. The new and old tie rod should have exactly the same end so your car will have the same handling properties, so it will not be too much “toe in” or “toe out”. The workshop will do the last alignment with reference to the manufacturer specifications after you take the car there. Tighten the tie rod adjustment screw so it will not rotate when the lengths are right.
Time to take the steering damper off. This is the easiest procedure, it is held in place with two bolts only.
One end is attached to the frame of the car while the other one is attached to the center drag link.
Now it is time to get the center drag link off, the procedure is the same here as with the tie rods. Except you don’t have to adjust anything.
The fitting is pretty much straight forward, but remember to use the right torque settings for the tie rod mounting nuts. You should tighten them down only to 41Nm, the tie rods will be stuck in the steering arm and the nuts have plastic inserts in them. Remember throw out the old tie rod ends nuts since thee plastic self tightening mechanism is word. The new tie rods and drag link comes with new nuts and be sure to use these. Loosing control of the car because of some old nuts would be as stupid as driving off a cliff.
You absolutely have to take the car to a workshop where they will do a new wheel alignment. This must always be done right after changing the lower suspension parts!