This might come as a shock to many of you, but I’m not an automotive engineer. I can appreciate the intricacies of like a car is designed and built, but if you gave me a factory and a blank sheet of graph paper the result would probably be more like the Homer from the LS400. However, I too can look at the front suspension of a W124 generation Mercedes and say, “Hm. There’s something wrong here.”
what it looks like worn out is the spring suspension used on cars with 4Matic all-wheel drive. Of course, adding front axles to a chassis originally designed for rear-wheel drive applications comes with some packaging issues, and the W124 is no exception. Those driveshafts needed to go right through the area that would hold the spring on an RWD car. Rather than moving that spring, Mercedes decided to simply redesign it and create the strangest looking single suspension component it has ever seen.
That spring bends around the CV axis. Normally cars will use a bracket under the spring to lift it, while the axle can pass through the bracket unimpeded (in the case of a coilover, this “bracket” would be integrated), but apparently Mercedes has decided to build the two together. in a single piece of metal. I asked David Tracy of Jalopnik what could have led to that decision, and he made a few theories:
I’m not a suspension engineer, but I’m an engineer, so you know I’m always happy to come up with a few guesses.
This rather inelegant setup is something that could be assumed to be the result of adapting a rear-wheel drive vehicle to use all-wheel drive. Oddly, Mercedes showed the W124 all-wheel drive – the first Mercedes passenger car with 4MATIC all-wheel drive – in 1985 as a concept car; this was shortly after the launch of the W124. I guess it’s possible that the W124’s front suspension was developed before the company decided to offer an all-wheel drive variant (which was launched a couple of years after the rear-wheel drive car in 1987). But that seems unlikely, as developing a car for both rear-wheel drive and all-wheel drive generally requires some forethought.
Either way, you may be wondering why Mercedes chose this path instead of just using a bracket mounted on the control arm for shaft passage and for a normal spring to mount on top. I guess Mercedes saw the benefit in having that extra single coil under the axle; Using a bracket may have resulted in a spool that is too short above the shaft, compromising the run / delivery. So maybe the company thought “orok, we can get a coil under the axis, we will just harden the coil and shape it around the motion envelope of the axis. “ This design likely allowed Mercedes to use exactly the same front control arms on both rear-wheel drive and all-wheel drive cars.
It’s truly a unique layout, something that has everyone on Jalopnik’s slack channel confused. You would think that the loads on that single length of steel must be very different from those expected by the steel coils. Is that length of steel heat treated to change its material properties so it doesn’t bend in a way that complicates suspension setup? Not to mention how big a breaking point the straight becomes in rusty environments; if the suspension fails, the top of the spring drops directly onto the axle, which seems like an easy way to triple your repair costs.
The springs – two of which are shown above, via an EBay listing – It also gave Mercedes the secondary “bonus” of third party incompatibility: the design is like this strange, no one has ever really bothered to replicate it. Forum discussion nach forum discussion is full of W124 owners looking for aftermarket front suspension parts – to lower the car, reduce body roll or just for the #hellaflush lifestyle. They always get the same answer: “Sorry. Go to OEM or leave it as is. “
I guess “leave it as is” is the solution then.
h / t: Antti Kautonen