Mercedes Benz 300

During the late 1940s, Daimler-Benz AG began focusing on building another powerful, elegant limousine for the luxury market, something in the spirit of the pre-war 770K. The 300 had been on the drawing board since 1938, and a prototype Cabriolet was shown at the Frankfurt Auto Show in April 1951. Production of the four-door Limousines and Cabriolet D began that November and ran through 1962, with 11,430 cars built.

This production average of 1,000 cars a year was definitely low, so updates were phased in as required and logged in by chassis number, a common DGAB procedure then. When significant changes were made, the model designation changed. The original 300 (no letter) was built as a 1951 to 1954 model; the 300b was built for 1954 and 1955, and the 300c for 1955 through 1957, and the 300d for 1957 to 1962.

The 300 quickly became one of the leading prestige cars of its era, and standard-wheel-base cars were brought by Frank Lloyd Wright, Yul Brynner, Al Hirt, Prime Minister Nehru, and the Shah of Iran, to name just a few. Early Cabriolet D prices of around 25, 000 DM (Which would have bought three Cadillacs) stretched to 35, 000 DM for the 300d version. These cars cost more than a 300SC Roadster or a 300SL Roadster with hardtop.

Among the many heads of state, royalty, captains of industry, entertainers, and other prominent individuals who relied on these cars was West German Chancellor Konrad Adenauer. Even though his custom-bodied 300d limousine differed from the standard version in many ways – among them a higher roof and extended wheelbase- all 300s soon bore the nickname "Adenauer." Continuing an already long Vatican-Stuttgart connection, Pope John XXIII’s specially-built 1960 300d Pullman-Landaulette had a closed front seat but a convertible top over a single, throne-like back seat. Even among 300 production cars, custom features were common.

Like certain other Mercedes-Benz models, the 300 was advertised and sold with different body style names in Germany and elsewhere. For the sake of marketing, the Limousine and the Cabriolet D in Germany became the more familiar sounding Hardtop and Convertible for the U.S. Elegant sales literature remains to the tell the story.

The last of this upright, honorable line was the 300d. By the mid-1950s the original 300’s conservative styling and other modest features were showing their age. More and more 300s were being exported to the U.S., where the sweeping lines and driving comfort ranked high among buyers’ expectations. In August 1957, DBAG began building the totally updated 300d.

To provide more rear leg room and a smoother ride, the new model’s W189 chassis had a 3.9-inch longer wheelbase. In the American vogue, the Hardtop’s dramatic new roofline-with no visible center pillar-combined with removable rear quarter windows to create a pillarless panorama. The tiny horizontal taillights of the earlier cars were replaced by much larger and easier seen vertical lights in the almost-finned rear fenders. A one-piece front bumper replaced the earlier three-piece design.

Like earlier 300s, the 300d was built on an oval-tube X-shaped frame with independent front suspension by coil springs. Because they also used a rear swing-axle, varying loads significantly affected rear wheel camber, which in turn influenced driving stability. DBAG’s solution to keeping the rear wheels upright was a unique load leveler. Controlled by a dash switch, an electric motor on the rear chassis wound a jackscrew in or out to twist auxiliary torsion bars acting on each ear trailing arm to supplement the coil springs. This device was used on all four 300-series cars; the hydraulic self-leveling systems on later models were not as durable and lacked manual control.

Beneath the long hood, protected by an oil-bath air cleaner, the M189 engine’s bore and stroke were 85x88 mm, displacing 2,996 cc. Unfettered by previously poor fuel quality, compression was now 8.55:1, and Bosch six-plunger mechanical fuel injection-instead of the earlier cars’ solex carburetors-helped boost output to 160DIN hp at 5, 300 rpm, the equivalent SAE being 180 hp at 5,500. Torque reached about 175 lb-ft at 4,200 rpm. Rather than the high pressure direct injection of the 300SL and 300SC, which was apt to cause oil dilution, the 300d injected the gasoline into the intake manifold, required much lower injection pressure. The rear-mounted electric fuel pump operated continuously, running surplus fuel back to the tank through a return line.

All 300d models bound for the U.S. got the Borg-Warner (AKA Detroit Gear) three-speed automatic transmission. An ATE T50/14 brake booster replaced the previous Treadle-Vac unit, providing 5:1 boost rather than the earlier unit’s 4:1. Bias-ply "Extra Special" tires measured 7.60-15, and the brakes themselves were upgraded. Up front, 10.2-in diameter finned drums were teamed with dual-action cylinders and floating brake shoes. Speaking of ratios, rear-axle gearing was low, 4.67:1; a 5.125:1 ratio was also listed. A 19-gal tank helped accommodate fuel mileage in the low teens.

Inside the 300d Hardtop, the previous wood headliner, susceptible to moth and water damage, was replaced by easier to clean perforated vinyl. A single pull-out ashtray beneath the dash gave way to a pair of ashtrays atop the dash. One change frustrates today’s restorers: the "Securit" logo on the side window glass was made smaller and repositioned. Convertibles were usually upholstered in leather, but Hardtop buyers could also choose corduroy velour. At the time, sales brochures also touted a fabric called "Dralon," but it remains a mystery. Both front seats reclined, and the rear seat has a huge fold-down armrest. Even without the optional divider window, passengers were surrounded by more than 21 sq ft of glass.

The optional headrests, on chrome brackets with collapsing hinges, can be removed and stored in cloth bags. Unless the top is down and the rear view mirror is rotated to the upper position, these huge headrests effectively block rear vision, so often only a passenger-side headrest was ordered. In the age of brylcreem and hair spray. Linen doilies protected the leather and the occupants’ hair from each other.

Of course, most 300s were delivered with a factory-installed radio and antenna. A dash-mounted fader knob controlled rear speaker volume, and the antenna was a Hirchmann automatic unit. A wooden faceplate insert filled in for the optional Reims short-wave adapter, rarely ordered on U.S.-bound cars.

By 1960, automotive safety was a growing concern, so the 300d steering wheel had a large, almost flat center pad, and the elegant dash lost it previous big chrome controls in favor of rubber-covered knobs. Two-speed wipers and a three-tone horn were fitted. The turn signals on European models operated via the horn ring, but U.S. cars used a conventional lever. The transmission gear indicator was relocated from atop the steering column to the left of the instruments. For the Hardtop, a metal sunroof was optional, along with a trunk-mounted air-conditioning unit.

To fill said trunk, 15-percent larger than that of the 300c, Mercedes-Benz offered up to six fitted cases, counting a cosmetic case and a hatbox and suitcases of three sizes. Matching leather hard cases were replaced in 1959-60 by similarly-sized soft cases; still, hard cases could be special-ordered on later cars. Special loops in the trunk and matching leather straps held the luggage in position.

Given the 300d Hardtop’s 4000-lb heft (4,585-lb for the Convertible), prodigious length, and compromised rear vision, driving a 300 required skill. The earlier models’ high center of gravity, lack of power steering, and manual transmission had never helped, either, but in the 300d, an automatic transmission, fuel injection, larger windows, and power steering could offer some assistance.

Unless you activate the kickdown, the automatic box departs in second gear, and by the time you reach 60 mph in third, the engine is spinning at 3,700 rpm. The automatic version required 18 sec to reach 60 mph, only a second longer than the manually-shifted four-speed version. (Today’s owners who complain of poor performance may need to properly rebuild these 40-year old transmissions.) Theoretical top speed was just over 100 mph, but most 300s spent far more time being driven far more sedately.

Conservatism was both an asset and a detriment. Many then-contemporary features such as V-8 power and disk brakes never made it onto the 300. Against a total of 3,077 Hardtop/Limousines, only 65 Convertibles (or Cabriolet Ds, if you wish) left the factory. The first soft top 300d was built in July 1958; only 16 were made in calendar year 1961, followed by a single example, the last convertible sedan built by DBAG, in early 1962. By then the totally new 600 limousine was being readied to assume the 300’s role as the premier luxury Mercedes-Benz.