W123 ‘84 300TD: I am completely stumped. I had to reseal the piston on the passenger rear caliper since it was scraping. The pistons were easy to get in and out and I am pretty confident that I did it right. But now as I try to bleed the brakes either using Mityvac or a friend press the pedal, no brake fluid is coming through. Pumping and pumping with no avail. I even disconnected the brake line to see if gravity will allow for the fluid to come down…nothing.

Update: tried bleeding driver rear and same thing…just air. To see if the piston seals hold pressure, I’ve pulled the said passenger caliper and applied vacuum to the bleeder valve while holding the brake hose opening at the caliper - the pressure held. I’ve even tried to pull brake fluid directly from the brake hose and same thing…just air.

I dropped the car and carefully checked the brakes. Although soft pedal, fronts still work.