Re-bleed master after leaving system open?
 

So I just resealed all 4 calipers. System has been open for a week. Am I supposed to re-bleed the master cylinder?

I've power bled all 4 calipers, but the rear brakes do not work when depressing the pedal. Fronts work though. When depressing the pedal, I get active fluid flow at the rear caliper bleed nipples.
Rear brakes only work if I pump the pedal, plus the pedal feels like it has no resistance. Thoughts?? Mc dead and bypassing?

Update, I pulled the master off. Pretty sure the piston for the rear calipers is bypassing. Maybe I've been running it like this for a looong time and just didn't know it?
I depressed the pedal and fluid actively squirts out the nipples for the front R and L calipers. Nipple for the rear brakes squirts fluid weakly and is constantly flowing fluid through it, as if the piston for it no longer seals properly

What car is this? If the rear brakes are fed from the forward reservoir chamber which is filled by overflow from the aft chamber, maybe there isn’t enough fluid in the chamber now or when you were bleeding.

Also, I think there’s a spring between the front brake piston and the rear brake piston in the master cylinder so you need full strokes to bleed the rear vs not so full strokes being sufficient to bleed the front brakes. If you meant pressure bled when you said power bled then stroke doesn’t matter.

Why would you leave the system open when brake fluid is hygroscopic?

Sixto
98 E320s sedan and wagon
02 C320 wagon

83' 300d turbo sedan

I took the calipers off to reseal them, then found that the rebuild kits that I have were incorrect. Took a week to get new kits and get it all back together.

I used a pressure bleeder (the Motive unit), which theoretically bypasses the pistons inside of the master entirely. Figured I could leave the system open because it's getting a full fluid flush anyways.

Why would fluid constantly pee out of the nipple for the rear calipers? Isn't it supposed to be sealed in? I can fill the reservoir and it'll all just dribble out if there are no lines attached to the Mc

what you are experiencing is very normal, infact when doing removal service on rear brakes and when mechanics dont want it leaking out, they have the brake pedal slightly pressed, this closes off the pressure circuits - meaning it closes off the port where it intakes fluid from the reservoir tank.

What you are experiencing is how "gravity bleeding" works in brakes.

Exactly.:)

If you put some plastic wrap (as a gasket) under the brake fluid reservoir fill cap you won't lose brake fluid.