1979 Mercedes-Benz 450 SEL 6.9 W116 – road test

Mercedes-Benz 450 SEL 6.9 W116 – aristocratically powerful. Very large engined Q-car, top of the Mercedes range (forgetting the W100 600 limousines), with enlarged 6.9-litre version of the W100 600’s 6.3-litre V8, automatic transmission and hydropneumatic self-levelling, height adjustable suspension in the longer wheelbase W116-series S-class saloon body. Introduced May 1975 as late replacement for the original W109 300SEL 6.9 made between 1968 and 1972.

The traditional picture of Mercedes-Benz, at least in British eyes, is one of big, powerful touring cars — not of the not-so-big family cars, actually rather under-engined, which are Daimler-Benz’s bread and butter.

Daimler-Benz do however make what is expected of them, and have done so for a long time. When the old W108/W109 S-cars were replaced by the new ones in 1972, there was no immediate replacement for the old 300SEL 6.3 W109, of which 6,500 had been delivered. Devotees of this earlier Q-car had to wait nearly another three years, until May 1975, before an over 6-litre V8 was installed in the new S-class; this was the 450SEL 6.9 W116, a larger-still version of the 6.3 engine, with a 107mm bore in place of the 6.3’s 103mm but the same 95mm stroke. With the new S-class W116, the old low-pivot swing axle rear suspension had (blessedly) been replaced with semi-trailing arms. Hydropneumatic self-levelling at the back had been an extra on the lower capacity, coil-sprung cars, but on the 6.9 it was made standard, and the springing itself is hydropneumatic, using remote gas-filled reservoirs connected by pipes to the damper struts. Weight went up with the new body by 6 per cent, from 34.1 to 36 ¼ cwt, but this would seem to be more than matched by the claimed increase in power — 14 per cent — and maximum torque — 10 per cent.

The figures in question are 286 bhp at 4,250 rpm and 405 lb ft at 3,000 (against 250 bhp at 4,000 and 369 lb ft at 2,800). The engine follows American practice in using hydraulic tappets for quietness, but is European in its single overhead camshaft per bank. It has aluminium alloy cylinder heads, a cast iron block, Bosch KA-Jetronic mechanical fuel ejection, and the unusual feature of (fry sump lubrication, something usually restricted to competition cars.

Performance

Instantly magnificent

Immediately you get into the 6.9, it begins as it intends to go on — instantly obedient. One is surprised then by the unsteady tickover, which allows a very perceptible tremor to be felt irregularly when at standstill in traffic; not a serious fault, for the engine never stalls, picking up perfectly when bidden.

The car’s acceleration is prodigious for its size and type. This is helped by its adherence to the German preference for undergearing overall, so that the autobahn driver, conditions permitting, nearly always has acceleration in reserve whatever the speed he is cruising at. The argument is that since top speed is somewhat academic at anything over 130 mph, it is worth sacrificing it on the altar of acceleration. And when a car is as fast as the 6.9, this is an understandable point. You can argue, equally right, that the correct gearing, which allows the car to achieve its absolute maximum speed (by permitting peak power revs to coincide with that speed), beside giving the car a higher “wot’ll-she-do-mister”, will improve cruising refinement and economy, at the cost of a little loss in top gear acceleration.

The interesting point here is that if it were correctly geared, how would its performance then compare with the obvious British rival, the equally superb Jaguar XJ 5.3? As things are, as the following table shows, it beats the almost identically powerful but better-geared V12 handsomely up to 60 mph, fails near enough level at 90 mph, and behind thereafter. (As a matter of interest, the Jaguar recorded a time to 130 mph, of 42.9 sec). Even bearing in mind that the narrower, lower Coventry car has around 12 per cent less frontal area (and therefore less drag), the realisation that the 6.9’s power peak engine speed is reached, at 121 mph, whilst the Jaguar is still on the climbing side of its power curve (the XJ peak is at 142 mph) prompts the thought of how much possible advantage is lost in the German machine’s undergearing. We have included figures for the 6.9’s very fine 4.520cc parent in order to show anyone interested the kernel of what they might be paying the extra £10,626 for.

Getting back to the 450SEL 6.9 W116, the figures show that it is magnificently quick for a four-seater saloon, whirling one back up to very high speeds in absurdly short time with contemptuous ease, making overtaking infinitely safer and very high average speeds safely possible.

It is, as we have said already, a marvellously obedient car. A squeeze of the accelerator pedal and you take that gap. Such easy refined power — the engine is commendably smooth in its working range — removes any excuse for bad-tempered driving, since when one opportunity is frustrated, one can so easily and safely make something useful of another which would be impossible for lesser cars.

Above: Wide angle lens view distorts good proportions of car seen from rear. Only obvious signs of what is under the bonnet are the hint given by the alloy wheels and the confirmation of the 6.9 on bootlid. Below: Engine compartment — a daunting sight. Car has two fans — extra one ahead of radiator (electric) is for air conditioning.

The gear range selector as before remains an example of how to arrange the controls of an automatic properly. In the first place, its movements are smooth and precise, and do not require unnecessary effort. In the second, it is beautifully and perfectly gated, both literally — the selector lever runs up and down in a slot very smoothly, rather like a manual gearbox gate on a Ferrari — and in the position of what are effectively locks to prevent the driver inadvertently moving the selector beyond. The gate slot is straight between D and S — the fully automatic and first/second-gear-only positions — so that the driver can flick the lever into second to change down manually and back to D in order to change up without unintentionally continuing into neutral — and over-revving dangerously.

The car will change up in D relatively early on light throttle, with a smoothness which is good if not quite in the same class as on big American cars, but much later of course if one drives flat out. Maximum automatic change points from rest are at 4,200 rpm (52 mph) and 4,600 rpm (90 mph) respectively, and maximum kick-down changes are at 80 mph from top to second and at 49 mph from second to first. For the acceleration runs, we found it saved nearly half a second to 60 and 1 sec to 100 mph if one held the changes-up to 4,900 rpm. The kick-down quality is quite good — immediate and with a jerk that is tolerable considering the inertia changes involved and the acceleration that near-instantly begins. The throttle control is as good as it should be on such a car, smooth and easy to use carefully, as one certainly needs to on the wet and slippery surfaces that were the rule for much of the test period. A limited slip differential is standard equipment, but even so it is of course very easy with just over 400 lb ft of torque to set the back wheels spinning and the tail sliding, making one wonder why when with all the undeniable Daimler-Benz ingenuity brought into play to make this truly super saloon they did not go the whole hog and give it some form of all-wheel drive. It certainly needs it in anything but perfect road conditions, if only to make less wasteful use of the power it has, since it should be emphasized that tail-happy driving of the 6.9 is easily avoided by the sensible driver.

A speed control is standard. It doesn’t initiate the acceleration as smoothly as a good driver will however, and unusually, you can feel the speed fluctuating when the cruise has been set; the fluctuations are small, around ± 1 mph, but they are noticeable. Another difference is in the setting of the cruise, which requires you to hold the lever appropriately for several seconds. This, say Mercedes, is so that an inadvertent flick of the lever does not set you cruising when you don’t mean to.

Noise

Not the quietest

Naturally, the W116 450SEL 6.9 is quieter than most cars by a large margin. But, perhaps surprisingly, it is not particularly quiet by any means. At town speeds, up to 40 mph, any acceleration is accompanied by a curious moaning noise which rises with engine revs, stemming possibly we suspect from the car’s hydraulics. On coarse surfaces the amount of bump-thump-generated tyre noise is most disappointing, and not anywhere near the standard set by Jaguar in this class. Some tyre whine is discernible as well and the sunshine roof generates some wind noise, which almost dominates engine noise at 90 to 100 mph. The engine itself is pretty quiet, especially when one is driving at up to 80 mph, but a noticeable heterodyne sets in at around 110 mph — which the very optimistic speedometer said was 121.

Economy

Good for its capacity

Considering its engine size and power, and the way any driver worth his salt will tend to use the 6.9, it is remarkably easy on fuel. Our overall consumption of 13.6 mpg is good for the class and interestingly not far behind that of the 450SEL (14.7 mpg), suggesting that the optimum engine displacement for this body is something nearer 7 litres than 4 ½. Driving which did not include performance testing returned consumption of around 15 mpg, with a best of 17.0. The 6.9 is not as good as the old 6.3 which returned 15.1 mpg overall, but then the latter s test mileage did not include any London driving, being conducted entirely in Germany and Italy, with some admittedly thirsty Alpine work thrown in.

Road behaviour

Generally, very well-mannered

The 450SEL class is blessed with perhaps the most pleasant power steering system we know. The fact that it is assisted is hardly obvious except when parking; there is excellent feel of what the front wheels are doing through the rim of the unusually large steering wheel (16 ¾ in.) It is accurate. And here for once is a manufacturer — Rover are one of the few others to do the same — who when they power-assist their steering take the opportunity to gear it up as well; for its size, the 38 ¼ ft mean lock of the Mercedes is not bad, and from lock to lock there are only 2.6 turns of the wheel. This gives the car superb response for a large saloon, and makes town manoeuvres so much simpler.

Straight stability is excellent except in side winds which trouble the car surprisingly, and when one puts the tyre pressures up to the high speed settings (34/34 psi two up instead of 32/32) when there is a faint suggestion of weave, probably suspension-induced.

Ordinarily, the roadholding is good, with just-understeering handling. Corner hard however, and the usual effects of semi-trailing arm rear end: are encountered, reminding one the Daimler-Benz stuck so long to their refined but still tricky version of a swing axle and that in their own parlance, this is a diagonal swinging axle — which allows camber changes during cornering and infrequent breakaway, particularly ii the driver is forced to decelerate in the bend. In this respect, although the 6.9 is perfectly safe and not truly treacherous, it is not a car for the inexperienced. It is very easy to set the tail swining simply with the right foot — but the rear end is a bit too skittish in its own right, without any power effects complicating matters. However, the competent driver will not be caught out — and even if he is, the beautifully quick steering provided enables him to master any waywardness with the minimum of drama.

Ride depends rather more than usually on speed. The W116 SEL is pretty firm at low speeds, pot holes and sharp-cornered bumps coming through quite markedly, with an accompaniment of thumping noises. At speed it is much better, coping very well yet hardly floating except when, Citroen-like — not surprisingly perhaps remembering the hydropneumatic common denominator — it fails to return to full downward travel front wheels which a hump has punched up into the wheel arches. We were impressed with the way it coped with French route nationale unevennesses, and amused at the little sigh made by the self-levelling after a deformation upset the level slightly. Even when you go over the noticeable but gentle top following a typical northern French road swoop at speed, there is an interesting correction of attitude a little way after the peak — the car arrives on the far side not nose high as normal cars do but nose perceptibly down — and there is a little jerk as it straightens itself level again, complete with that sigh. The car also has a curious crosswise rocking motion, hard to explain.

The brakes, discs front and rear (ventilated in front), work well for all normal purposes, with the right sort of pedal effort — 60 lb maximum — without being too light and over-sensitive, and returning an excellent 1g best stop. The handbrake, worked via one of the few pleasing umbrella-type mechanisms we know, is disappointing, returning barely over 0.2g and not holding the car on 1-in-3. Returning to the main brakes, our fade test prompted us to wonder at the wisdom of using the same size brakes on this 140 mph 36 ¼ cwt car as those on the 11 8 mph 31 ¾ cwt 280S W116.

Above: Spare wheel lives underneath boot floor. Below left: Handle under side of seat allows seat height to be adjusted. Driving position is excellent. Below right: Room in the back is adequate. Note netting for magazines and so on behind front seats.

Going by pedal effort required, the Mercedes kept within reasonable bounds, even though the effort needed for the last two stops rose to a maximum of 60 per cent more than that needed at the end of the first stop. Noticing smoke from the front at the sixth stop, and some sponginess in the pedal at the ninth one, we inspected the discs after the tenth and found them red hot. On cooling down they recovered as usual and all seemed well until the next day when the pad wear warning light glowed intermittently.

Inspection by Mercedes-Benz (Great Britain) showed that although the pads still had plenty of life in them, the pad wear sensor wires had shorted, probably because of the heat during the test; replacement wires cured the problem. We also learnt that alternative harder pads are available if customers require them. Later, looking up the original driving impressions of the car published in Autocar 17 May 1975, we remembered that, after a “long winding descent back to base” at the end of the demonstration test circuit, “most drivers provoked the front brakes to smoke” although (it is added) “nobody reported any sign of fade.” That rather parallels our test, which in terms of pedal pressure, which is what matters, showed up tolerable fade. But we wonder about the very high disc temperatures which are possible, even on a pretty cold day.

Behind the wheel

Masterfully simple

The driving position is the typical epitome of the German type — excellently straightforward, with generous spacing of pedals, seat and that big steering wheel whose rim frames the instrument pod so neatly. In spite of the complications typical of Daimler-Benz under the skin of the car, in the driving compartment it is pleasingly simple and honest, and easily understood by the newcomer.

One key, square-headed, is the driver’s, fitting every lock on the car which even if there were not the magnificent Mercedes vacuum-operated central locking system — so quiet compared with other people’s electric ones — makes life simpler. Another, round-headed, can be left with a garage or parking attendant, and does not open the boot. The central locking looks after fuel flap and boot, as well as doors, as all such systems should.

An extra switch in the facia works the ride height adjustment which is one of the benefits of hydropneumatic suspension. Not as high-ranging as Citroen’s, it nevertheless allows you to raise the car by about 1 ½in, for slow driving over rough going, or to lock the suspension when it is being lifted or transported.

Heater cum air conditioning controls are well laid out and easy to understand in spite of the fact, unique to Mercedes, that you can have your side of the front of the car cool while your passenger, who may have different heat sensitivity, has their side warmer. Since such differences between people, especially couples, are by no means uncommon, this is a very welcome thing which Daimler-Benz have provided for over 20 years but which no one else seems to have bothered to copy, which is a pity. It is allied to air-blending control which works near perfectly, giving you any temperature you want, although the progression from hot to cold is initially a little severe. Some testers complained that the floor heat flow in front misses out the feet, leaving them cold.

Vision out of the car is good enough but not ideal, because of the very heavy pillaring of this tank-like body. The screen pillars cause a notable blind spot and, when you have to look sideways or over the shoulder, so do the B-posts and rear quarter panels. The wiper arcs are quite good however, with their unusual near-centre pivots, and the speed with which the rear screen demister removes ice made us wonder what current it uses; its switch is fitted with an automatic timer preventing it being left on longer than about 25 minutes. Another good point is the way the back window clears itself of rain at speed, showing that airflow there is unusually clean for a three-box car.

The driver’s seat is highly satisfactory too, and although it has no Rolls-Royce type electric motor assistance, you can alter its height as well as rake, thanks to the very clever two-cradle, inclined plane design of the seat pan. Headroom however for a 6ft driver is only just adequate on the lowest setting, with only about an inch to spare between the head and headlining. Legroom is what it should be in such a car, adequate for our tallest testers.

Living with the Mercedes                          

As may have been gathered, this is largely a great pleasure. For all its faults, the test staff found themselves — rather unusually — falling heavily for this Mercedes. The main reasons are obvious; the way it goes and steers. But the small things are endearing too. It has delay courtesy lamps, which stay on after you shut the door for 15 sec — a detail, not uncommon today on better cars, but very useful. The quietness of the central locking has been mentioned, but not the fact that if you have locked yourself in and then use the door releases to get out, this automatically undoes the locks, unlike some other cars. The heater fan is very unusual in being pretty powerful yet not noisy. The ashtray is one which can be removed for emptying without that initial jerk which scatters half the contents all over the carpet; smoking drivers would however prefer a right-hand one in the driver’s door as well as this central one in front, which they described as a little too small. There is effective side-window defrosting. Door pockets are as usual very welcome; we thought the lockable glove compartment a little mean. Americans will find the electric windows too slow; they take nearly six seconds to open or shut fully which compares badly with most transatlantic cars so fitted. The front seat belts, their reels and vertical runs very neatly hidden in the B-posts, are the ideally simple buckle-less sort where you just close a latch on them. We thought the loud buzzer which reminds you that you have removed the ignition key leaving the headlamps on unnecessary. The halogen headlamps are superb, with a good cut-off on dip and useful range on full beam; their aim is of course helped greatly by the self-levelling, so that you are unlikely ever to blind anyone unless you are late with the dip switch. We would not expect many owners to concern themselves under the bonnet with anything beyond topping-up reservoirs. The bonnet itself is unusual in having two safety catches, one each side of the grille, so that you have to use two hands to lift it.

The W116 S-class range

The 450SEL 6.9 W116 is of course king of the lofty S-class castle, at £28,621. Beneath it lie the 450SEL, at £17,995 the only other long wheelbase car, then the 450SE with the same 4 ½ -litre V8 but 4in, off the wheelbase which costs you £869 less; the remaining V8 saloon which is the 350SE at £15,81 5 and finally the only S-class saloon available with manual or automatic transmission, the six-cylinder 2.8-litre 280SE, at £13,578 in either version. There are of course the S-class sports cars and the coupe-saloon, respectively the 350SL R107 (£15,655 manual or automatic), the 450SL R107 (£16,736 automatic only) and the 450SLC C107 (£19,710 automatic only).

The obvious competitors for this ultimate Mercedes are numerous; we have not tested any of the fast-dwindling American possibilities, and even if we had, we suspect that nothing made on the other side of the Atlantic approaches the current European class in this field. Unfortunately, we haven’t tested an automatic BMW E23 735i/733i (manual figures are given but the price is for the two-pedal car) or the current big Ferrari. The Ferrari price is for the automatic 400GT, which uses a 340 bhp 4,823cc engine in the same body as the manual 365GT 2 + 2 whose performance data is given.

The figures speak for themselves. If rear seating isn’t as important as pure poke, the two sports thoroughbreds win, if pressed hard on top speed by the Jaguar. The Mercedes 6.9, under-geared slightly as it is, wins on the more practical 0-60 saloon acceleration stakes; the fact that it is so very close to the two Grand Touring cars gives a good idea of just how deceptively quick it is. The Jaguar does either slightly more or slightly less than the 6.9 much more quietly; its nearest rival in value for money (not that close a rival) is the very efficient BMW. We have included the 450 Mercedes to show once again where its big brother wins and loses. Note how little there is in it in fuel consumption.

ON THE ROAD

Best behaved in roadholding and handling is probably the Aston Martin, closely accompanied by the Ferrari and the Jaguar. The three German cars all use semi-trailing arm rear suspension which works well except in extremis when, particularly if the driver decelerates, camber change limits grip. The two’ Mercedes do, however, have power steering which is as good as anybody else’s and better than most, with perfect weighting and feel, unlike the over-light XJ system. In ride, the genuine saloons are understandably better than the GTs, with Jaguar arriving at the best overall compromise between ride and handling. In response, none have bad brakes, but we do feel that fade resistance is borderline on the 6.9 in view of its performance and weight. As far as noise is concerned, if you like the right sort, it’s a matter of taste — Aston’s snarl-y V8 or Ferrari’s highly-musical V12. But if refinement is the point, then without any doubt there is nothing here to approach Jaguar.

SIZE AND SPACE

It is interesting to note that the Mercedes body has the best amount of legroom in spite of having the shortest wheelbase, suggesting that Daimler-Benz have been particularly efficient in the proportion of body-to-passenger space they have achieved. None of these cars has a poor driving position, although the Ferrari’s betrays its native country in favouring the shorter man with long-ish arms, if not as much so as on many other Italian cars. Not having driven automatic versions of the BMW or Ferrari, we cannot comment on gear selector layout and quality for the whole group; of the known automatics, both the Aston Martin and the Mercedes are blessed with the proper if all too rare arrangement of safety stops — and in the Mercedes case there is the added joy of what is probably the best selector movement available anywhere.

VERDICT

Obviously, if it is pure performance that is wanted — and taking into account the inevitable inefficiencies of torque converter and epicyclic which will probably not be offset adequately by the extra power of the 400GT — the automatic Aston is king; an immensely pleasing car for the enthusiast. The BMW offers an approach to the performance of the other bigger capacity cars which is certainly less thirsty — but how much that counts for in this company is open to debate. It is, relatively, a fussy contender too. The W116 450SEL offers nearly everything that its even more expensive alternative gives so easily, and does so remarkably well. Top of the class is fought for very evenly by the 6.9 and the XJ. The Jaguar dominates easily in refinement, not so easily in ride, has better roadholding, and is ultimately faster. The Mercedes’ advocates will point to the more practical lower end of the performance where the 6.9 is faster. Both are tremendously satisfying cars of the highest calibre. Considering that the Coventry machine is less than half the price of the Stuttgart one, yet does most things just as well and several appreciably better, the Jaguar is the better car — but only just.

PRODUCED BY: Daimler-Benz AG, Stuttgart-Unterturkheim 60, Postfach 202, West Germany.

SOLD IN UK BY: Mercedes-Benz (United Kingdom) Ltd., Millington Road, Hayes, Middlesex.

Left hand dial on the dashboard has fuel, oil pressure and water temperature gauges 260 kph / 170 mph speedometer has press-to zero trip 7.000 rpm revcounter (on right) has red line at 5,300 rpm and an inset clock. Warning lamps below instrument pod (from left) are high beam, brake pad wear, height control, with indicators at each end and trip and panel lamp rheostat in between. Height control knob is hidden behind wheel. Excellent lamp control switch is just visible on right. Stalks (right) control signalling, and wipe wash (combined in one) and speed control. Horns work from any part of steering wheel crash pad — very convenient. Heater, ventilation and air conditioning controls are on centre console above excellent Becker radio. Switches above in centre are for electric sunshine roof, heated rear window and (right) rear interior lamp. Window lifts are worked from rocker pads behind gear range selector Above: A wet road makes this sort of thing ail the easier to provoke.