A low or "soft" brake pedal isn't abnormal on the V8 & V12 W140 chassis as they have a SPECIAL solenoid on the master cylinder. That solenoid changes the proportion % of the brake fluid flow to the rear brakes. Going straight the rears get 37% of the pressure & in a corner that changes to 28% (like most other MB's). IF you think the pedal is going to the floor have someone depress the pedal & put your hand between the pedal & the carpet to see if there is any travel left. THERE is a big "hump" in the carpet that makes you think the pedal is too LOW!
Have replaced several $1,500. master cylinders on those cars with NO change in pedal position!

HAVE the brakes been bleed with the solenoid activated?

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator