"WINNER of the 1973 Car Of The Year Award, the Mercedes 450SEL represents the very pinnacle of passenger car development." So said Autocar in May, 1974. Four inches longer than the otherwise identical 450SE, the L has, in normal Mercedes tradition, needed little in the way of modification in four years to retain its place as the flagship of the Mercedes range. The 450SEL 6.9 has for us been something of an enigma - they kept changing the conversation whenever the subject was brought up! Anyway, with my memories of driving the earlier "low pivot" trailing arm swing-axle 280SE 3.5, and being fairly frightened on occasion, it was going to be interesting actually to find out for myself, albeit a little late, how Mercedes had engineered their way out of trouble; and the effect on handling/roadholding of lots of anti-dive and detail geometry changes at the front, and the "diagonal swing-axle, with starting torque compensation", meaning lots of anti-squat, and a Watts linkage at the rear.
It appears to be the rule of "progress" in the development of a generation of cars that weight increases in proportion to the time in gestation. This leads to the need for a bigger engine, which in turn increases the weight further still, and so on. Weighing 4cwt more than the earlier 280 V8 (in some part due to the extra body length), the 450SEL and all post-1973 cars, was introduced with a torque convertor-equipped, three-speed automatic gearbox, as opposed to the earlier fluid-coupling transmission. More power and torque-sapping - yes - but quite the smoothest change I have ever experienced, ranking with the very best US units. Full throttle upward changes take place at 45 mph and 85 mph. A stroked version of the 3.5-litre V8, the current 92mm by 85mm, 4,520 c.c. unit must give the claimed 225 bhp (DIN) at 5,000 rpm, and 270 lb ft torque (DIN) at 3,000 rpm, because it manages to haul 35cwt from zero to 60 mph in just over 10 sec (my approximate timing), 70 mph taking another 3.5 sec on average. I found that these times could not be improved much by holding the lowest ratio. Originally fitted with Bosch L-Jetronic, all-electronic fuel injection, Mercedes have now reverted to the K-Jetronic all-mechanical system, in the interest of simplicity, and workshop floor serviceability. However, "constant injection" (the L system is timed from the distributor) and emission-control changes do nothing for fuel economy at 13.4 mpg, against 14.7 mpg for Autocar's "Car Of The Year". In fact all the performance figures were slightly down from the earlier car.
The standard of equipment and general finish could not really be faulted, and detail improvements to the switchgear and ventilation controls worked well. Introduced right from the start on the 450Series were some very worthwhile aerodynamic subtleties, in the guise of sophisticated screen pillar and rear window guttering, aimed at keeping the side windows clear of waterborne dirt. Warm air is also ducted into the front doors, and in turn to the windows to prevent misting. Even the rear light lenses are aerodynamically designed to keep clean!
"Alright, Mr Salesman; I will have one, you have convinced me," yet I am not sure. I will try to develop the thought that I have concerning the relationship between the car and its likely purchaser, wealthy, middle-aged, and (I venture to suggest) prone to consuming a little too much food, and much worse, drink.
As previously explained (and in common with the whole German motor industry) Mercedes have engineered themselves out of swing-axle handling and roadholding shortcomings by clever development of the same basic rear suspension. Without going into considerable detail, the latest system locates the rear wheels with a semi-trailing wishbone, angled downwards from the chassis to provide the anti-squat, and what amounts to a Watts linkage formed by a link attached to the wishbone, at the bottom, and the roll bar link at the top of each rear back-plate. The combination of anti-squat and good torque location, has enabled previous self-levelling devices to be dispensed with.
A swing axle will always be a swing axle, or so I thought. the problem is that, in order to achieve the ride characteristic expected in such a car, springing has to be soft. More than a usual amount of pitch and roll control is left to the anti-dive and squat, together with roll bars which are stiff in relation to the weight of the car. Unfortunately, roll bars are connected transversely and dramatically raise the overall spring rate when in use. Large one-wheel bumps can affect the opposite side of the car quite noticeably, as did a high motorway crosswind, producing a rather upsetting "roll rock" condition. At the same time I have always found that the addition of anti-squat and dive tend to negate feel. Anti-squat in particular often seems to "fight" free movement of the rear suspension when cornering hard.
Having said all that, and left you wondering where all this is leading, just bear with me. In spite of some shortcomings in the basic system, then, Mercedes have managed to develop the suspension to such a degree that there is no feeling whatever of a swing axle behind one, rather something of rigid-axle stability, but without the feel such an axle provides both at and around the limit of adhesion.
Now to driving - first and immediate impressions were of silence, and isolation from the surrounding melee, quite excellent and relatively direct power steering, with 2.7 turns from lock to lock. By a system of reaction valves in the steering box, making the steering effort sensitive to tyre contact friction, the application of large amounts of lock, as when parking, is made easier. The servo action is therefore effort-sensitive rather than speed-sensitive, as with most progressive systems.
Here comes the point - the 450SEL is quiet (a recent change to Michelin XWX has helped earlier road noise complaints), almost totally lacking in wind noise at high speed, comfortable, almost soporific in fact with cruise control set up, fast and easy to drive. But it is not easy to sense the limit of adhesion, because every recent development seems to have been aimed at, or has by chance resulted in insulating the driver from his surroundings. Thus I found myself having to correct lines through corners consciously, and pay a great deal of attention to speed limits, so effortless and deceptive is the performance. I can imagine the post-prandial businessman nodding off at the wheel quite easily, but then the reduction of so-called stress is what passenger car development is all about, is it not? I have never found that the feeling of being in contact with the road, as opposed to being insulated from it, a stressful condition. On the contrary, it gives the driver confidence and a feeling of control.
The fact is that one "at grips" with the SEL, it is delightful to play through a corner, entering with mild understeer, changing to neutral on the way out. A spinning rear wheel (no diff lock) releases over-exuberance. Racking the car at high speed from lock to lock, the rather springy suspension travel can be felt, but I am over-critical - this is a big, executive car. The brakes, though powerful and light, lock at the front too early, though with very little reaction through the steering (anti-dive again). It follows that wet weather braking could be more of a problem.
Perhaps this will be the last time a member of the Autocar staff gets to sample an S-class Mercedes, as it is suspected that a model change is in the pipeline. How can they improve an excellent car? Trade some isolation for feel, and tune the brakes, for then one would become a Mercedes driver, not just an owner.
© 28 January 1978 AutoCar, UK.