Can’t Bleed Brakes
 

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.

Top up the brake resovior to maximum there is a weir which seperates the front from rear fluid in the tank. First fronts get filled the way up top the rears start to get filled.

^^^ Yup X2...look closely into both sections of the reservoir to confirm that they are filled with brake fluid.

Oh man! You guys were right! The reservoir is so foggy that I assumed it was full, but by shining the light I discovered that the front part of the reservoir was empty after all. Do I need now to bench bleed the master cylinder or can I just fill it up and keep bleeding?

Just bleed

Absolutely not. Just fill to the brim and bleed away.

Thank you all. Problem solved. The front brake reservoir really needs to be filled high enough to allow for the flow to the rear brake reservoir at the front. Also caliper rebuild is super easy, so save the $$$ and do it yourself.

Nate taught me a trick I used for hard to get air out of lines. Had me use a stick to hold brake pedal to floor over night. it worked all air gone. make sure brake lights are not on, disconnect battery.