All suspension systems are a compromise in the quest for good handling and a pleasant ride. Early 1950s Mercedes 300 sedans included an electrically activated torsion bar to keep the rear level regardless of ‘payload’. 1960s solutions became a bit more sophisticated. The leveling devise became hydraulic — mounted over low pivot, swinging rear axles. The 1960s also brought Mercedes-Benz‘s first full-fledged air suspension with no springs under the car. This used to spook mechanics, but compared to today’s cars 1960s models are a walk in the park, deserving mileposts in the history of suspension technology.
Springs have advanced too. Most significant has been wide adoption during the 1980s of progressive rate springs. This is a great example of less-is-more: only one part accomplishing a friendly ride on the boulevard while becoming firmer as the spring gets more compressed. This is made possible by asymmetrical coils: measuring from the center, one half of each spring has more loops than the other half. More loops require more wire. The longer the wire, the less its strength. The softest portion compresses first becoming stiffer as the middle and other end get compressed.
Earlier Mercedes engineers flirted with these results using two springs. One was smaller and mounted inside the main spring. Only one end of the inner spring was fastened and the other end only made contact when the softer outer spring compressed more than a third of its potential travel. 300SL Coupés have this design in the rear.
In addition to ride and handling, engineers vary spring rates fore and aft to compensate for engine weight and estimated ‘payloads’ — a major variable from one person to five plus a full trunk and gas load. Just returning your favorite car’s suspensions to original condition can double driving pleasure, literally change the car’s personality. In the time honored practice of critical incident management (a.k.a. fire fighting) it is likely previous owners totally ignored their suspension unless it began eating tires. If your car is a keeper start with the basics like tie rod ends, bushings, upper control arms (which become subtly oval and wiggle under the heavy loads), shock absorbers and a fresh alignment. Then consider going further.
Air pressure alone will make a noticeable difference in cornering behavior. While low pressure was responsible for many of the Ford/Firestone tire failures, car enthusiasts more often err on the high pressure side. A car’s absorption of the road irregularities relies on a combination the tire flexibility and suspension working together. Simple cracks in pavement are easily accentuated by minor over inflation. Dropping pressure just one or two pounds can catch a sweet spot where the whole car rides better. Tweaking an alignment job, changing anti-sway bars (for example 1960s 6.3 front anti-sway bars can be fitted to 1960s SLs), or adding wider tires, will have the indicated results.
Mercedes Benz seldom re-manufactures “optional” springs after production of a series ends but those other spring specifications right down to wire thickness, installed and uninstalled heights, become public knowledge for posterity (and after-market vendors). One of the most popular upgrades is progressive rate springs for 1950s and 1960s sedans and SLs. This is not authentic but goes unnoticed by car show judges. Those years (all M-B models) had conspicuous nose dive in braking and body lean in corners even when new. The 1980s 190E sedan was the first Mercedes to use progressive springs as standard equipment.
Shock absorbers manufacturers Sachs, Koni and Bilstein, all differ from their American counterparts in doing approximately 80 percent of their work on the rebound stroke, only 20% on the initial compression. This is also true for adjustable shock absorbers which only alter that 80% rebound absorption ratio about 15%. Most American shock absorbers have closer to 50/50 absorption of strokes in both directions, with adjustable versions rarely exceed 60/40, 50/50 or 40/60 options. German engineers reason that it is the spring’s job to manage the car’s sprung weight and the shock absorber’s primary job to mute a spring’s recoil behavior. Otherwise the shock absorber is doing the spring’s job. As an aside, many shock absorbers can be rebuilt, often locally. Rebuilding anything is out of fashion in these days but older Mercedes parts were designed to be rebuilt: water pumps, generators, alternators fuel pumps, etc. Mechanics seldom mention it but the cost is often one third of new parts.
Another pitfall: low profile tires & larger wheels. Pre-1986 SL suspensions “expect” round edged tires. Ignore this and risk “wandering” steering, but that’s another subject.
MBseek.com / SL Market Letter has developed progressive rate and sport springs for all Mercedes-Benz cars from 1926 through 1989 (Click here to visit our Sport / Progressive Rate Spring page). They are made to order for your specific Mercedes Benz vehicle as there are too many models to inventory.
If your car is a “keeper” and you sense your springs allow too much body lean or nose-dive when braking, call us at the SL Market Letter offices in Minneapolis, Phone: 612-377-0155 to learn what is available for your car.