The electrical system. A land of wonder and fear for many, but fear not since it is often less complicated than it seems. Electronics and electrics are here to stay and thankfully Mercedes are pretty reliable on this area with few exceptions.
Ever experienced that the remote IR key fob for the W140 have stopped working even after the batteries are replaced? This can generally one of two issues:
The key fob needs to be synchronised again with the car. This happens due to loss of voltage on the chip when batteries are completely dead for a while.
One component fall off due to old solder and mechanical stress over time.
Checking functionality and proper voltage
This is a very simple task. Point the IR towards your face and hold the button for one second at least. A red light will blink if the key fob works and the battery is OK. If not change batteries and look for the red blink. The battery type is 2x of CR2025 or CR2032 with 3V. If there is no blink, you need to open the key fob and maybe do some soldering. When the blink is OK, try to see if it can open the doors. If not, then it needs to be synchronised.
Synchronising the key fob
This is a very easy job, make sure you have good batteries and the key will give a blink if you hold the button for at least one second. In order to synchronise it, go inside the car. Point the key towards the mirror and press twice at the button in rapid succession. Then within 30 seconds put the key in the ignition and turn it to position 2 without starting the engine. After you do this operation the key should be synchronised with the car, then you can check again if the IR key will close and open the doors. Retry this procedure if your are not successful.
Fixing loose components inside key fob
This is a bit more tedious and require you to do some electronics fixing.
In order to do this job you will need a solder iron and some solder wire to fix it. Make sure you have flux cleaner after soldering to clean up the mess. To get the case open you need some small flat head screw drivers and a sharp and narrow knife to cut the glued case. For securing the case at assembly, you will need some glue. I can recommend Loctite 406 rapid super glue.
Now you have figured out that the key fob is not blinking a red light after you swapped batteries. So you need to open the key to inspect the electronics. The plastic key case is glued together and it needs a bit of fiddling to get it open. Follow the pictures below.
Now your key fob should be working again and not come apart.
The major issue with this car which basically prevents me from driving it is a malfunctioning front window wiper mechanism. It rains quite a lot here especially in the autumn, also it’s illegal to drive without them. While the front window wipers are essential, the rear one is not working either. Side view mirrors are often enough, however the mirrors on this car are so small and “well” designed so you can’t really see whats directly behind you. So I will need to fix that one as well.
The front wipers were almost not working when picking up the car when I bought it and the wipers were stuck in a weird position. Unfortunately it was heavy rain this day and not really possible to drive without it. When inspecting the mechanism it turned out that the motor was fine, but the wiper bracket was broken due to a totally seized right side wiper shaft.
After some 2 hours of fiddling in the rain we managed to get the driver side wiper to work (barely). The drive home was quite interesting where I operated the wiper only when strictly necessary. Thankfully it worked all the way home with no fuzz.
Front Wiper Mechanism
The access to the front wiper mechanism is easily made with removing the plastic cover just over the engine beneath the front window. But first open the hood to get better access to the wiper arms. Some care here is needed so you don’t crack the front windscreen, such as dropping your tools and slamming the spring loaded wipers on the window.
Removing the wiper arms can be a challenge if you don’t know the trick. Unscrew the nut half way, then use an open ended wrench to pry off the wiper arm and voila it’s off. Once both wiper arms are removed, you can remove the plastic guard cover. It’s only held in place with 6 hex screws located at the top of the engine bay. Take care not to loose any tools or screws into the engine bay. You will never find them again from the bottom of the engine bay.
The wiper mechanism itself is easy to take off. There is one cable to the motor, then the mechanism is held together with 3 bolts. When reinstalling a used one, or refreshing the existing one. It’s an excellent opportunity to lube the wiper shafts with some oil and put some grease on the mechanism joints. Much easier than when it’s on the car.
Before reinstalling the wiper mechanism, make sure the joints are installed the correct way. Use the article as reference since there are two ways the joints can attach to the middle pivot bar. Installing them the wrong way might ruin the assembly when turning on the key. Also beware that the motor is really powerful, so don’t put your hand or fingers down in the mechanism while someone is turning the key or checking the mechanism from inside the car. Ideally the battery should be disconnected while working on the wipers.
Before assembling the whole thing, make sure the wiper mechanism works properly by turning on the wiper motor and inspect that the mechanism works without any issues and clears all obstacles under the windshield. There is some wiggle room for the bracket in the 3 mounts. Then you can put back the plastic cover.
Installing the wiper arms is probably the most difficult with this job, since it needs some fiddling and adjusting to get the correct angle. The two arms are not equal either so make sure to put them on correct to their assigned side. When aligning them, you will need to try them out and see if they have enough clearance when operating while also cover most of the screen. This might take a couple of tries, so be patient. When they are aligned, then put back the plastic covers and your are done.
The issue with this type of wiper arm design is that the wiper arms seem constantly to fight for position. If one binds or get stuck the other wiper will most likely break the other arm with a punch! A problem in older cars with more non-synchronized wipers like these is that they end up fighting for the windscreen and the wiper arms get bent, for example Lamborghini Espada.
Feels good to have working wipers again!
Rear wiper mechanism
The rear wiper motor is easier to replace. First remove the wiper arm, or if it’s broken off like mine, remove the nut. Then open the rear hatch, there is a plastic cover under there which can be removed without tools. Just use a plastic prying tool to snap it open.
The wiper motor has a plastic tube which needs to be unhooked. The plastic tube delivers wiper washer fluid to the rear window. Don’t worry, it will not leak water when unhooking it. Don’t mess up the plastic spring, otherwise you will leak washer fluid into the boot. Also unhook the power plug.
The window motor is held in place by only three bolts, and when removing these you can slide out the whole motor from the rear.
A new rear wiper blade comes actually wih a new arm as well, since the wiper blade is quite special and non-standard. It is not super cheap, buit not expensive wither. Installation is just reverse of disassembly, remember to test it and check for leaks before finishing at the end.
My experience so far with working on this car is that it’s actually super easy to work on. It seems that if a car is easy to assemble on the factory thus making it cheap, it will also be easy for the home DIY mechanic to do work on. I’m quite happy for that. Older cars are usually more complex in their build and also a bit harder to work on.