It was based on the extended-wheelbase version of the W116 S-Class platform, introduced in 1972, but equipped with an M100 V8 engine from their flagship Mercedes-Benz 600, uprated to 6.8 l, and featuring full hydropneumatic suspension, licensed from Citroën.

Mercedes-Benz system had the separate pumps for brake boost, power steering, and hydropneumatic suspension, citing the better failsafe measures than Citroën in the event of a hydraulic failure.

The Mercedes-Benz system contained the hard rubber dampers that served as temporary springs and allowed the car to be driven if the hydraulic pump or components failed.

Mercedes-Benz suspension system has the feature that maintains body level without squatting at the rear or diving in the front during the acceleration and braking respectively.

Initially, Mercedes-Benz did not plan on selling the 450SEL 6.9 in the United States given the oil crisis that hit the Americans very hard and increasingly tightening emission regulations.

[3] The 6.9 was fitted with four sealed beam 5.75" round capsule headlights with bezels and larger impact absorbing bumpers that lengthened the car by 11 inches.

[11] Despite the higher retail price, the interior of the 450SEL 6.9 was indistinguishable from the other W116 models except for the different type of wood trims, height adjustment knob, and two extra warning lamps in the instrument cluster for the low suspension pressure warning and height adjustment indicator.

Heated seats for driver and front and rear passengers as well as electric sunroof were extra cost options.

No power-assisted external rear view mirrors and seat adjustments, commonly fitted to luxury cars such as Cadillac and Rolls-Royce during the 1970s, were ever offered in the 450SEL 6.9.

The automatic HVAC system was adapted from Chrysler Corporation and had a compressor from Harrison division of General Motors.