Backing down a driveway, I had to panic stop for a truck. Brakes worked fine, hard pressure on the pedal, but then the warning light went on. Checked the reservoir, near dry. Had enough brakes to make it home. Filled the reservoir, bled it, but still need to bleed the whole system (It's frickin 4 degrees out!). Pedal travels about 3/4 before pressure.
Is there anyway to check the master cylinder? I poured a lot of fluid in, can't seem to fill it -- could it be leaking into the power booster? Any other advice?

 

If you can't find any signs of an external leak than yes it's possible the main seal on your master cylinder is shot and is leaking into the vacuum booster.

 

Took off the master cylinder, no fluid at the push end. Cleaned nit up, put it back on. Bled front right, RL, no air. FR had some. Broke the bleeder on the right rear. Drill and tap? Easy-out? Forced for a new caliper? All of the above?
BTW, brakes still go 4/3 to the floor. Saw no leaks anywhere. Dash brake light is still on.

 

are you going through fluid still?
if no your master may be shot

 

Not sure if it's still loosing. Replaced the caliper (frickin bleeder valve), then bled every caliper. Got a ton of air out of the rear, no air from the front. Had good pressure on the pedal, but then started it up and pedal went to the floor. (I know the booster had to be charged up). So now back to square one.
The ABS is a Kelsey Hayes (?), 2 lines from the master in, 3 lines out. Is there a way to bleed it? There's to caps on opposite sides on large flat "bolts," and 2 large hex fittings, as if for a huge allen wrench.
It's getting cold here in Cleveland. Going to let is set overnight to see if it's losing any. Have not seen any leaks anywhere, but plan to get underneath and trace every line.
PIA!