Take the pads out and dump the fluid Rudy.
Replenish the fluid and bleed the system.
As you are operating the rear brake, check that there is a slight swirl in the reservoir as the pedal is released, if not, it means your m/c piston is not retracting fully.
This is essential.
Press the slave cylinder piston back into the caliper and operate the pedal, the piston should pump out progressively…(don’t go too far).
Also clean and grease the pins that the rear caliper slides on. If the caliper cannot slide, you are only getting effect from one pad and brutally loading the disc.
Clean the disc thoroughly.
Try all that stuff.
