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(from Mercedes-Benz
Press Release) The first with eight cylinders: the 107 series
(1971 to 1989)
-- A total of
237,287 open-top two-seaters produced in 18 years
-- Engines again and again updated to reflect the state of the
art
-- Coupés of the SLC series available until 1981 parallel to the
open-top version
In April 1971 a new SL
rolled out onto the highway, the Mercedes-Benz 350 SL. For the first
time in the history of the model series an eight-cylinder power
plant did duty under the long bonnet. From all sides it made the
impression of a strong, self-confident, imposing open-top vehicle.
Its fathers also gave it an equally well designed, removable coupé
roof for the road. Besides elegance and quality the body radiated
safety, since the crash behaviour of the two-seater was far ahead of
its time.
Difficult decision
The decision to
manufacture the R 107 series ("R" as in Roadster instead of "W" as
in Wagen = car) was taken by the Board of Management after intensive
debates on 18 June 1968. At dispute was whether there should be a
Targa-roof version, i.e., one with a removable roof panel, instead
of the fabric-topped variant, because owing to higher safety
standards alarming news was to be heard from the USA regarding the
licensing of open-top cars.
That a decision finally
was made in favour of an open-top two-seater with a fabric roof and
an additional removable hardtop can be attributed to Hans
Scherenberg, the head of Development, who fought tooth and nail for
it: "The SL gave me great pleasure, but also caused me great
trouble. This was no easy decision for us," he summed up the
decisive meeting.
The coupé question still
was unanswered, however. It was not decided that day. Discussion
centred around whether one should additionally, and soon, make a
four-seater sports coupé based on the R 107 series, or wait for the
coming S-Class (W 116) to build it on that basis. But then a
production model would not have arrived until much later, in the
mid-1970s.
Karl Wilfert, then the
head of Body Design in Sindelfingen, developed – pretty much on his
own authority – a coupé based on the R 107 and presented it one day
to the Board of Management as a "rough draft". Rejected at first,
Wilfert managed to push through his idea of a sports coupé with the
tenacity which was so characteristic of him.
And so six months after
its premiere the SL was followed in October 1971 by a comfortable
four-seater Sports Coupé, the 350 SLC, whose unconventional lines
also found it many friends around the world in the course of the
years. Internally the series was designated C 107. Up to the
windscreen its appearance matches that of the open-top variant;
behind the windscreen the overall height and length grows. A flat
roof spans the four-seater passenger compartment in a gentle curve,
going over into a large and very steep rear window that arches in
two directions. The boot lid is slightly convex in shape, unlike the
SL's.
In the side view the
length of the Coupé is documented, firstly, by the 360 millimetre
longer wheelbase (2820 millimetres versus 2460), secondly by the
line of the side windows. Without awkward B-pillars they are
completely retractable, as is usual in a Mercedes-Benz Coupé. The
SLC's coefficient of drag is better than that of the SL so that the
Coupé attains the same performance despite an added weight of some
50 kilograms.
A particularly
noteworthy fact is that it fully lived up to its classification as a
"Sports Coupé", gaining wins for Mercedes-Benz in many rallies and
long-distance races.
Safety as agenda
Béla Barényi's safety
concept with front and rear crumple zones and a rigid passenger cell
found expression in the 107 series in a further developed form. The
backbone of the R 107 series is not simply a shortened and
reinforced saloon floor assembly, as in the predecessor, but an
independent frame-floor unit with a closed transmission tunnel and
box-shaped cross and longitudinal members which featured differing
sheet metal thicknesses and a resultant carefully defined crumple
pattern.
The SL definitely had to be an open-top car, and that being the case
the only protection in a possible roll-over would be provided by the
A-pillar plus windscreen. They were thoroughly redesigned and had 50
percent more strength to show than in the previously built version.
In addition, to enhance its strength the windscreen was bonded into
the frame. This resulted in a remarkable power of resistance in the
roof-drop test with the result that the open-top car could be
licensed for the USA even without a Targa bar. To complete the logic
the rear window of the hardtop also was bonded into its frame.
Even in the interior
there were pioneering changes to report. The hard dashboard made way
for an ingenious sheet-steel design that yields on impact both in
the top section and the knee area and is foam-padded. The switches
and levers were recessed. Another new feature: the four-spoke
steering wheel based on the latest findings of accident researchers.
The proven impact absorber was still in place, but the
steering-wheel rim, spokes, padded boss and hub were covered with
polyurethane foam. As further safety feature the fuel tank was no
longer installed in the rear end but above the rear axle, protected
against collision. From March 1980 the anti-lock braking system ABS
was offered; from January 1982 also airbag and belt tensioner.
A bestseller right off the bat
But it was not the
safety aspects that motivated customers around the world to quickly
reach for the new SL. It was the promise of an open-top automobile –
the only one offered in the USA over a period of several years –
that was a successful piece of work in every respect. Its
distinctive front end with the dominant SL face, the wide-band
headlamps and grooved indicator covers had a powerful aura; the
lines of the low silhouette were harmonious – soft top open or
closed, or with hardtop. And the very slight inward curve of the
boot lid, along with the concave hardtop, were reminiscent of
"Pagoda" days. The wide-band tail lights with their ribbed surface
not only were largely insensitive to soiling, but additionally gave
the rear end a touch of vigour.
Extremely conducive to
comfort and ease of operation was the easily and speedily operated
soft top, a refined version of the "Pagoda" top. It took just 30
seconds to open or close it. Folded, it disappeared underneath a
cover that was meanwhile customary in the SL series.
A number of details
underscored the car's safety aspirations. The seats were available
from the start with head restraints, and seat belts also were
included. Physical well-being and driver-fitness safety were served
by the heating system with its very spontaneous response, supported
by new air ducting at the doors. Newly developed wind-deflecting
mouldings on the A-pillars, which also served to channel off
mud-laden water in the rain, and dirt-repelling covers on the
exterior mirrors enabled good visibility. They kept the side windows
clean even in inclement weather. The windscreen wipers arranged
closely to each other in the centre of the car swept a respectable
70 percent of the windscreen area, were always optimally positioned
in the flow of air and did not lift off even at higher speeds.
Engines with catalytic converter
During its 18-year
"lifetime", which was not planned to last that long, but in the end
was indeed successful, this SL got a whole series of six- and
eight-cylinder engines. Its model designations accordingly are quite
varied.
The eight-cylinder
models were led by the 350 SL (1971 to 1980), whose 3.5-litre engine
(M 116) already was known from the W 108, W 109 and W 111 series.
The 147 kW which it delivered at 5800 rpm helped the SL, which did
weigh 1600 kilograms after all, to clock nine seconds for 0 to 100
km/h and reach a top speed of 210 km/h. The 350 SLC had identical
performance figures.
From autumn 1971 onwards
the 450 SL also was produced. Its engine (M 117) developed an output
of 165 kW at 5000 rpm. Top speed was 215 km/h, and it needed 8.8
seconds to go from 0 to 100 km/h. In 1972 the corresponding Coupé
version, the 450 SLC followed, with identical engine and identical
performance. Prior to March 1973, both were destined exclusively for
export to North America; after that they were included in the
general sales range.
In July 1974 the SL
model range was extended: as a consequence of the oil crisis of
1973, the SL and SLC now were available as models 280 SL and 280 SLC
with the 2.8-litre M 110 engine. It developed 136 kW at 6000 rpm and
had proven its reliability in the two years before in the "Stroke
Eight" series W 114/115 and in the W 116-series S-Class. Both models
had identical performance: the top speed was 205 km/h; sprinting
from 0 to 100 km/h in 10.1 seconds was possible.
So three SL engines now
were available – nowadays nothing unusual, but in those days
something new in the history of this model category. Only the
attentive observer could distinguish between the three variants: The
280 SL could be recognised by its narrower tyres in comparison to
the 350 SL and the 450 SL. In addition, the 450 SL featured an
inconspicuous front spoiler which was attached to the rear lower end
of the front apron and distinctly increased the radiator's air
throughput.
Between November 1975
and February 1976 the fuel injection systems of all three engines
were changed for better compliance with the emission standards,
which meanwhile also had become stiffer in most European countries.
The electronically controlled Bosch D-Jetronic was abandoned for the
newly developed mechanically controlled Bosch K-Jetronic. The
changeover entailed minor losses in performance in all three cases:
in the 280 SL to 130 kW at 6000 rpm, in the 350 SL to 143 kW at
5500 rpm, and in the 450 SL to 160 kW at 5000 rpm.
At the same time the
compression ratios of the 2.8 and 3.5-litre engines were slightly
reduced. The 3.5 and 4.5-litre engines additionally got a
contactless transistorised ignition and hydraulic valve play
compensation to facilitate maintenance.
The compression ratio of
the 2.8-litre unit was raised to the old figure again in April 1978.
With a few supporting measures the engine then regained its earlier
power potential of 136 kW, but now already at 5800 rpm.
In September 1977
Mercedes-Benz launched the 450 SLC 5.0 with a V8 engine (M 117)
enlarged to a displacement of five litres. A hidden innovation was
the first-time application of hypereutectic cylinder contact surface
machining, which made it unnecessary to insert cylinder liners. The
engine delivered 177 kW at 5000 rpm, good for zero to 100 km/h
acceleration in 8.5 seconds and a top speed of 225 km/h. The
vehicle's bonnet and boot lid were made of aluminium, and it had
light-alloy wheels as standard. On the outside the 450 SLC 5.0 was
recognisable by, among other things, a narrow spoiler on the rear
end.
Revising the series
At the Geneva Motor Show
in March 1980 the SL and SLC presented themselves in updated form.
The interior appointments including steering wheel were matched to
those of the 126-series S-Class, and the engineering was brought up
to the same level. The previous three-speed automatic transmission
with torque converter was replaced with a four-speed variant. Models
280 SL and 280 SLC were given a five-speed manual transmission as
basic equipment. In addition, the hardtop now was included in the
standard specifications of the open-top variant. But above all the
light-alloy eight-cylinder engines of the 126-series S-Class,
slightly modified, made their arrival in the 107 series. The
six-cylinder engine of the 280 SLC remained unchanged.
The new 500 SL, equipped
with the 5.0-litre V8 (M 117) familiar from the 450 SLC 5.0,
replaced the 450 SL and made an output of 177 kW at 5000 rpm
available, to give the new top-of-the-range model a 0 to 100 km/h
acceleration of 7.8 seconds and a top speed of 225 km/h.
Models 350 SL and 350
SLC were sent off into retirement after nine years of production.
Their successors were the 380 SL and 380 SLC, whose 3.8-litre
light-alloy engine (M 116), with 160 kW at 5500 rpm, originated
after the pattern of the five-litre unit, by enlarging the bore of
the long-serving 3.5-litre V8 with grey cast iron cylinder block.
Both models attained top speeds of 215 km/h and needed nine seconds
to go from 0 to 100 km/h.
From the outside the new
models were almost indistinguishable from the previous models,
except for the model plate. All three SL models now had a
light-alloy bonnet and the discreet front spoiler familiar from the
450 SLC 5.0; the 500 SL also got a light-alloy boot lid with black
plastic rear spoiler, already familiar from the five-litre Coupé.
In autumn 1981 both V8
engines were thoroughly redesigned in the context of the
"Mercedes-Benz Energy Concept" to reduce their consumption and
pollutant emissions. Along with an increase in compression ratio the
measures comprised camshafts with changed valve timing, air-bathed
injection valves, and an electronic idling speed control. Owing to
the altered camshaft tuning the maximum torque could be shifted to a
lower engine speed range and, in the case of the 3.8-litre engine,
even increased. This power plant underwent particularly far-reaching
changes: to get a more favourable volume-to-surface ratio the bore
was reduced and the stroke increased. The modified 3.8-litre V8 thus
had a slightly larger displacement. In both eight-cylinders, in
exchange, so to speak, for the improved economy, minor losses in
power had to be accepted, output dropping to 150 kW at 5250 rpm in
the 380 SL and to 170 kW at 4750 rpm in the 500 SL. As in the 126
series the final drive ratio was adjusted to the changed engine
characteristics and made higher, from 3.27 to 2.47 in the 380 SL and
from 2.72 to 2.24 in the 500 SL.
For the SLC Coupés these
changes came too late, however: at the Frankfurt International Motor
Show in September 1981, along with the "Mercedes-Benz Energy
Concept" the 380 SEC and 500 SEC models of the C 126 series were
presented, spelling retirement for the SLC models, which had been
built for exactly ten years.
But even after ten years
of production no thought was being given to a replacement for the SL
models. Four years after the Energy Concept was presented, they even
came in for extensive refinements, and so in September 1985, again
at the Frankfurt show, a completely revised SL model range was
introduced. The emphasis was on a restructured engine range. A
discreet facelift, primarily recognisable from the front spoiler and
wheels with aluminium rims (diameter: 38.10 centimetres), was also
part of the package. The front axle was done over and the brakes
enlarged with fixed callipers. To prevent the cars from pulling to
one side during braking, the steering offset was reduced.
Comprehensive model refinement
package
All engines were
available in two versions: with a catalytic converter and slightly
less output, and as so-called catalyst retrofit version without
catalytic converter. The catalyst retrofit versions could be fitted
later on with a catalytic converter, for example when the widespread
supply of unleaded petrol was ensured, and had their ignition
system, electronics and cable harness prepared for this.
A newly designed
3.0-litre six-cylinder engine (M 103) which had made its first
appearance in the 300 E of the mid-range series W 124 nine months
earlier replaced the tried and tested 2.8-litre engine, as it had
already done previously in the respective S-Class Saloon. As a
result the 280 SL was discontinued, and after a 22-year interruption
there was again a sports car with the magic model designation 300
SL. It delivered an output of 138 kW at 5700 rpm without catalytic
converter (top speed: 203 km/h; 0 to 100 km/h in 9.6 seconds) and
132 kW with catalytic converter (200 km/h; 9.9 seconds).
A new edition to the
range was the 420 SL with the 4.2-litre V8 engine (M 116), which at
5200 rpm delivered 160 kW without and 150 kW with catalytic
converter. It was created by adopting the bore of the original
3.8-litre engine and combining it with the stroke of the
"post-Mercedes-Benz Energy Concept" 3.8-litre engine, and now
replaced that unit in the SL, the S-Class Saloon and the SEC Coupé.
The 420 SL accelerated from 0 to 100 km/h in 8.5 seconds (with
catalytic converter: 9 seconds) and attained a top speed of 213 km/h
(205 km/h).
The 5.0-litre engine (M
117) also was modified; with catalytic converter operation in mind
it now had an electronic ignition system and the
electronically/mechanically controlled Bosch KE-Jetronic injection
system and developed an output of 180 kW at 4750 rpm. With catalytic
converter the output was 164 kW at 4700 rpm. These values helped the
500 SL attain a top speed of 225 km/h (with catalytic converter: 215
km/h) and accelerate from 0 to 100 km/h in 7.3 seconds (7.8
seconds).
The most spectacular new
development in the engine range was a 5.6-litre eight-cylinder (M
117), which was created by increasing the stroke of the 5.0-litre V8
and gave the SL an output of 170 kW at 4750 rpm. The 560 SL was
reserved to the export markets USA, Australia and Japan. Fitted with
an emission control system in the US version it had a top speed of
223 km/h and sprinted from 0 to 100 km/h in 7.7 seconds.
Production of the R 107
series ended in August 1989, more than 18 years after the production
start-up of the 350 SL. With that this SL series set an internal
record that probably never will be broken: in the entire history of
the company no other passenger car series has ever been produced
over such a long period. All told, in Sindelfingen 237,287 open-top
cars were built, a number which impressively demonstrates the great
popularity of the 107 series. Of the Coupé a total of 62,888 were
built from 1971 to 1981.
The R 107 series in the press
In a first test of the
Mercedes-Benz 350 SL auto motor und sport, Germany, No. 9, 1971,
wrote: "Good suspension comfort, definitely up to saloon standard,
proves to be an essential feature of the 350 SL: at low and high
speeds it absorbs big bumps well and takes small bumps in a way that
they never are a disturbance even on very poor roads."
In 1986 Road & Track,
USA, No. 11, 1986, compared the Mercedes-Benz 560 SL, which was in
the last era of its production, with the Cadillac Allanté and summed
up: "Legendary quality is Mercedes' primary stock in trade. But
brilliant performance and outstanding ABS braking have freshened it
this year. Against these attributes, Cadillac brings better handling
and greater luxury to bear while failing to match Mercedes'
performance and quality."
