The 6.9 was the first Mercedes-Benz to be fitted with the hydropneumatic self-levelling suspension system introduced by Citroën in 1954, unlike the 600 and 6.3 which employed air suspension.

The benefit of this arrangement is progressive springing.
The more the enclosed air in the suspension is compressed, the more difficult it is to compress; thus the suspension rate changes in proportion to the load.

Using a combination of fluid-filled struts and nitrogen-filled pressure vessels or "accumulators" in lieu of conventional shock absorbers and springs, the system was pressurized by a hydraulic pump driven by the engine's timing chain.
Compared to the new Mercedes-Benz system, Citroën's was belt-driven, exactly like a conventional power steering pump; failure of the Citroën system thus might result in loss of suspension.
The 6.9 was shipped with hard rubber emergency dampers that served as temporary springs and allowed the car to be driven in the event of a hydraulic failure.
The special hydraulic fluid required by the system was stored in a tank inside the engine compartment.

Ride height could be altered by a dash-mounted push-pull knob under the speedometer that raised the car an additional two inches (50 mm) for increased ground clearance.
This feature was deleted for the U.S. market, where height adjustable suspension was illegal from 1974 to 1981, due to bumper height regulations.

The suspension system gave the 4200 pound (1900 kg) car the benefits of both a smooth ride and handling that allowed it, in the words of automotive journalist David E. Davis, to be "tossed about like a Mini."
The car also featured a model W3B 050 three-speed automatic transmission unique to the 6.9 and a standard ZF limited slip differential both for enhanced roadholding performance on a dry road surface and enhanced traction in inclement weather.

Four-wheel disc brakes and four-wheel independent suspension were standard across the W116 model range.
The 6.9 was the first Mercedes-Benz to be fitted with the hydropneumatic self-levelling suspension system introduced by Citroën in 1954, unlike the 600 and 6.3 which employed air suspension.
The benefit of this arrangement is progressive springing. The more the enclosed air in the suspension is compressed, the more difficult it is to compress; thus the suspension rate changes in proportion to the load.
Using a combination of fluid-filled struts and nitrogen-filled pressure vessels or "accumulators" in lieu of conventional shock absorbers and springs, the system was pressurized by a hydraulic pump driven by the engine's timing chain. Compared to the new Mercedes-Benz system, Citroën's was belt-driven, exactly like a conventional power steering pump; failure of the Citroën system thus might result in loss of suspension. The 6.9 was shipped with hard rubber emergency dampers that served as temporary springs and allowed the car to be driven in the event of a hydraulic failure. The special hydraulic fluid required by the system was stored in a tank inside the engine compartment. 
Ride height could be altered by a dash-mounted push-pull knob under the speedometer that raised the car an additional two inches (50 mm) for increased ground clearance. This feature was deleted for the U.S. market, where height adjustable suspension was illegal from 1974 to 1981, due to bumper height regulations. 
The suspension system gave the 4200 pound (1900 kg) car the benefits of both a smooth ride and handling that allowed it, in the words of automotive journalist David E. Davis, to be "tossed about like a Mini." The car also featured a model W3B 050 three-speed automatic transmission unique to the 6.9 and a standard ZF limited slip differential both for enhanced roadholding performance on a dry road surface and enhanced traction in inclement weather.
Four-wheel disc brakes and four-wheel independent suspension were standard across the W116 model range.
Mercedes-Benz 450SEL 6.9