stareatsun

I have an 89 LS in front of me, and there is somehting weird going on with the brakes.
I have done plenty of brake jobs before this on many different cars, but I can't figure this one out.

My girlfriend started complaining about poor breaking, so I drove it around a bit and notices that the brakes were barel working, or the pads were really worn out.
I changed the front pads and rotors and left the calipers alone. I didn't touch the rears at all.
I didn't bleed the brakes initially, and when I did it today, the rear drivers side and the front passangers side have barely any fluid comming out of them. The other 2 calipers bleed fine and there was no air in them at all.

My question is, are there issues with the calipers? Master cylender? Proportioning valve?

The brake fluid in the resivoir is black, but the fluid comming out of the 2 good calipers is normal color.

Also, there was bunch of fluid comming out of the resivoir, but after tightning the clamp, it seems to have stoped. Could that have been related?

Any help is appriciated!