Rear Suspension on Pagoda SL

[Micky C]

Hi
I am the lucky owner of a 1964 230SL, fully restored. I have a question about the rear suspension. There is a horizontal spring above the pivot point of the rear axle, which when I do the vector force diagrams in my head, seems to increase the degree of roll when cornering, like an inverse roll bar. I have seen it called a "stabilizing" spring in the reading I have done. obviously, I am just too stupid, but can anyone tell me what function it performs?
Thanks
 

[Jack the Knife]

I had never seen such a spring likewise prior to 113 ownership. It is much the same as Porsche using a leaf spring beneath the rear axle. Supposedly it helps resist vertical axle movement. I could be totally wrong about this and welcome a correction, but I believe the spring helps keep any camber changes to just the one wheel being effected by a bump or dip in the road. In other words, it works like a camber compensator. I looked around and found this great picture on wikipedia which helps illustrate what happens if you do not have this spring or something similar: https://upload.wikimedia.org/wikipedia/commons/thumb/6/63/Swing_Axle_Diagram.svg/1920px-Swing_Axle_Diagram.svg.png

Note the rebound. I believe that is when the spring comes into play. You might notice that Pagodas dive quite a bit with the standard spring setup. By stiffening up the front suspension, I believe that significantly helps the rear maintain camber. I do not know why Mercedes did not utilize a De Dion tube in lieu of all this, as they certainly had experience with those on their race cars, except maybe owing to cost and complication, or perhaps sacrificing ride quality (but I have no experience with cars that use such a suspension setup, though I do want to buy an Iso Rivolta...).

I've found there's not a ton of information written about Mercedes' swing axle innovations at least in English on the internet. It's worth noting that post-Nader, I believe for a year, Chevrolet did use a similar compensator spring on the Corvair before going to a fully independent rear suspension. Mercedes should have offered such a suspension on our cars from the beginning, as Jaguar had done on the much cheaper XKE two years before the 113 was offered to the public...

[ja17]

The "low pivot" on the Mercedes swing axle made it much more resistant to "tucking-in" under hard cornering unlike the Corvairs and other cars with similar swing axles. With this design the pivot was moved to the extreme low point of the rear suspension. During hard cornering the axles tend to stay in proper camber. Previous models MB did not use this improved low pivot swing axle and handling suffered. The 300 SL Gullwing used the double swing axle (similar to VW). With the introduction of the 300SL roadster, Mercedes used the new "low pivot" design which improved the handling of the roadster greatly over the gullwing. The 190SLs and most other sedans of the era all used the low pivot rear axle with no spring until the "Finback" sedans and Pagodas when the spring was adopted into the design. The very latest versions of the low pivot swing axle , used a hydropneumatic  compensator unit instead of the spring, but was never used in the Pagoda for some reason. The multi-link Mercedes rear suspensions, which were used in some other models as early as 1967, were lighter with better handling than the old heavy swing axle.