This may come as a shock to many of you, but I am not an automotive engineer. I can appreciate the intricacies of how a car is designed and built, but if you handed me a factory and a blank piece of graph paper the result would probably look more like The Homer than the LS400. Still, even I can look at the front suspension of a W124-generation Mercedes and say, “Hm. Something seems off here.”
What seems off is the spring setup used on cars with 4Matic all-wheel-drive. Obviously, adding front axles to a chassis originally designed for rear-driven applications is going to come with some packaging concerns, and the W124 is no exception. Those driveshafts needed to go straight through the area that would’ve held the spring on a RWD car. Rather than moving that spring, Mercedes decided to simply redesign it — and create the single oddest-looking suspension component I’ve ever seen.
That spring bends around the CV axle. Normally cars will use a bracket under the spring to elevate it, while the axle can pass through the bracket unimpeded (in the case of a coilover, this “bracket” would be built in), but Mercedes apparently decided to build the two together into a single metal piece. I asked Jalopnik’s own David Tracy about what might have led to that decision, and he did some theorizing:
I’m no suspension engineer, but I am an engineer, so you know I’m always happy to throw out some guesses.
This rather inelegant setup is something that one might assume is the result of adapting a rear-wheel drive vehicle for all-wheel drive use. Oddly, Mercedes showed the all-wheel drive W124 — the first Mercedes passenger car with 4MATIC all-wheel drive — in 1985 as a concept car; this was shortly after the W124 launched. I guess it’s possible that the W124's front suspension had been developed prior to the company deciding to offer an all-wheel drive variant (which launched a couple of years after the rear-drive car in 1987). But it seems unlikely, as developing a car for both rear-drive and all-wheel drive generally requires quite a bit of forethought.
In any case, you might wonder why Mercedes chose this route instead of just using a control arm-mounted bracket for the shaft to pass through and for a regular spring to mount on top of. I’ll guess that Mercedes saw advantage in having that single extra coil below the axle; using a bracket may have resulted in too short of a coil above the shaft, compromising ride/handing. So perhaps the company thought “okay, we can get one coil under the axle, we’ll just harden the coil and shape it around the axle’s motion envelope.” This design probably allowed Mercedes to use exactly the same front control arms on both rear-drive and all-wheel drive cars.
It’s truly a unique layout, something that confused everyone on the Jalopnik slack channel. You’d think the loads on that single length of steel must be quite different than what’s expected by the steel coils. Is that length of steel thermally treated to change its material properties so that it doesn’t deflect in a way that complicates suspension tuning? Not to mention how big a point of failure that straight length becomes in rusty environments; should the suspension fail, the top of the spring is coming right down onto the axle, which sounds like an easy way to triple your repair bills.
The springs — two of which are shown above, via an eBay listing — also gave Mercedes the secondary “bonus” of third-party parts incompatibility: The design is so weird, no one ever really bothered to replicate it. Forum thread after forum thread is filled with W124 owners looking for aftermarket front suspension parts — to lower the car, reduce body roll, or just for the #hellaflush lifestyle. They’re always met with the same response: “Sorry. Go OEM or leave it as-is.”
I guess “leave it as-is” is the solution, then.
h/t: Antti Kautonen