Reviewed by Unique Cars and Parts
Our Rating: 2
WHEN THE MERCEDES S-CLASS replaced the o!d series of big cars in 1972, there was no new equivalent of the old 300SEL 6·3, a car which might be described as the ultimate Q-car. However, the omission was rectified in October of 1975 with the introduction in Germany of the 450SEL 6·9, a car that was in effect the existing 450SEL with a much bigger engine developed from the 6·3 litre unit.
The 6·9 litre version of the 450SEL was not, however, a pure performance conversion but was developed as a near-ultimate car in several respects, For this reason, it was provided with a completely new Mercedes-designed hydropneumatic suspension
to give self-levelIing, adjustable ground clearance, a softer ride and much better damping.
was standard in the 450SEL 6.9, and a limited-slip differential was used. The suspension
geometry (as in the standard 450) gave anti-dive and anti-squat stability. Once you were used to the 200 or 240D the 6·9 presented no problem. The controls, the instruments, the view were aII the same: only the performance was different.
The performance was certainly there in plenty. A standing-start acceleration on a short stretch of level road saw fulI-throttle up-changes at 80 and 150 kph in a very short time, to the accompaniment of a steady push in the back which marked out the truly accelerative car.
quality however did not match the smoothness of the big American units: it was very smooth changing up at fuII throttle, but gave slightly jerkier changes when the car was driven gently. Kick-down was smooth but sometimes unwilling to happen quickIy, especially when asked to shift from intermediate to low ratio.
If the performance is one of the 6·9' s raisons d' etre,
is another. The hydropneumatic suspension
would feel good when the car was climbing with lots of power in use; on the descent with a near-trailing throttle however it would feel underdamped, more so at the back end. This was probably because the anti-squat rear suspension
design, first seen on the 450SEL, played a part in firming-up the ride.
The ride would not seem outstanding until you switched again to an "ordinary" 450SEL; then you would notice the harshness of the steel-sprung ride, especialIy at low speed and over broken surfaces. This harshness was one of the few defects of the standard S-class cars, and the hydro- pneumatic suspension
completely overcame it. Despite the slight floating sensation when travelIing downhill on a closed throttle, stability remained excellent and roII angles were small. The Mercedes-Benz power steering
set the standard for others in all respects - feel, precision and gearing. The handling
of the 6·9 was impeccable. It was heavier than the 450, but only a little of the increase was due to the bigger engine, which scaled 350kg compared with 300kg for the 4·5- litre unit.
The balance of the car was little disturbed and with its even wider tyres
215n O-14, with excelIent Michelin XWX as standard it had the roadholding to cope with its weight and performance. Although you could provoke the front brakes
to smoke after repeated heavy braking, few mtoring journalists detected any sign of fade. One of the nicest things about the car was the smooth action and freedom from backlash of the brakes
and accelerator: combined with the anti-dive, anti-squat suspension geometry, that made it remarkably easy to drive smoothly even when trying hard downhilI.
The noise level inside the car did not meet the highest standards. Most of the noise was tyre
rumble. Given tyres
of this size - as RolIs- Royce had found - it was almost impossible to kill all the noise; some of which was transmitted not through the suspension
but directly from the tyre
tread to the inside of the wheel arch. MechanicalIy, the 6·9 is as quiet as could be: neither engine nor transmission
were audible except when accelerating hard and nearing peak revs.
Despite its size and price, the Mercedes 6·9 litre was still essentialIy a driver's car. The quality of the Stuttgart development engineers, all keen drivers and with the authority to back it up, showed through at every corner. Riding in the back was comfortable enough, and there was room to spare for a large passenger behind a large driver. But the ride felt better in front and in any case, it was only the driver who could appreciate why the car cost so much. The dashboard layout was scarcely changed in the 6·9 but air-conditioning
was standard and a ride-height control (situated below the speedometer
) is added. The speedometer
read to 280 km/hour, and the car had a claimed maximum is 225 (140 mph). Rev limit was 5,000 rpm.
Outward signs of the 6.9, by comparison with the 450SELfrom which it is derived, were confined to the badge on the boot lid, and slightly wider tyres. Under the skin there were considerable differences apart from a 53 percent increase in engine size, including the hydropneumatic suspension