I rebuilt the calipers and reinstalled and the car was on blocks for a long time. During that time most of the fluid leaked out of the brake lines. When I reinstalled I have now complete two massive bleeding efforts. the brakes work, but not completely correctly or the way they used to. I am wondering if i have a failing Master Cylinder. It makes an odd farty noise while I was bleeding. Originally I thought this was just the booster making a noise since the motor was not running. Now I am starting to wonder if the sound indicates a loss of pressure in the MC itself, and its time to replace it. OEMs are 350 bucks, so I'd rather not do it unless I know its the problem.

Anyone have to replace the MC, and what made you sure it was failing?

 

likely still have air. though, my system also makes some kind of groan-y noise when I bleed from time to time. i replaced the brake master cylinder in an effort to hunt down a brakes issue (was pads) but it turned out the bmc was good. it usually does not fail. if you want one, i've got mine for sale lol.

 

Last time I saw one fail was when the brakes were being bled and every time the pedal was pressed brake fluid would leak out of the seals between the cylinder and the reservoir.

 

If the BMC is bad, then the pedal should slowly sink when holding the brakes firmly. Check with engine running so you get the full force.