Developed as a sportier version of the model 600, the 1968 300SEL 6.3 used the same fuel-injected engine as the grand 600. In addition, the 6.3 borrowed the hydraulic air suspension system of its big brother. This car lacked very little in the way of mechanical sophistication and was billed as "The fastest sedan in the world." The 6.3 was only offered in the four-door 300SEL sedan body, forcing it to compete with the more plentiful but tamer 450SEL in today's market.
The 6.3 exhibited incredible roadholding characteristics for its day. Combine this with the 300 hp engine and you have what amounts to a "big, bad wolf in sheep's clothing." The car was capable of doing 0-60 mph in 6.5 seconds and had a top speed of 140 mph. Even though the 6.3 was described by Road & Track as "The greatest sedan in the world," it is still a sedan. Had it been offered as a convertible, it would surely be the most valuable Mercedes-Benz produced in the 1960s!
As with all later-model collector cars, it is wise to find a car in the best condition you can afford. Parts on the low-production 6.3 are available, but very expensive. Also remember that as the car becomes more sophisticated, maintenance becomes more difficult.
The complicated air ride system of the 6.3 can be a real headache and the transmission can develop harsh shifting problems. Otherwise, if carefully serviced, the 6.3s are trouble free. Watch the rear axle; it's unique to the 6.3 and will break with excessive use of the available power. These cars are true thoroughbreds and demand special attention. At the time of this printing (1986), the 6.3 is one of the best bargains around, when considering potential future value.