After I had the rear wheel cylinder replaced on the left rear wheel, the brake pedal still goes all the way to the floor
A sinking pedal is often a sign that there is a leak somewhere in the brake's hydraulic system. Sometimes a problem of this nature may render a vehicle unsafe to drive, as braking systems relies on sealed pressure to operate. I would thoroughly inspect all 4 wheels, and underneath the vehicle for any obvious signs of leakage. If no obvious visual evidence is found, I would then suspect a problem with the master cylinder. Master cylinders usually fail due to internal sealing issues, so a thorough diagnosis of your braking issue by a mechanic would be recommended.
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