Sinking brake pedal

[misnomer]

Car is an '89 SOHC with no ABS and stock brakes.

I noticed this morning that my brake pedal is sinking. I'll hit the brakes, car slows, but the pedal sinks. Correct me if I'm wrong, but doesn't this indicate bad master cylinder? I had replaced the rear brakes a month or three ago, bled the brakes then. All seemed OK. THe brake booster and master cylinder were replaced a few years ago.

Any ideas?

[91rusty240sx]

its most likely the master cylinder, if you replace it, make sure you bench bleed it before installing it, otherwise, youll just have the sinking pedal again.

also, it may be caused by the proportioning valve. when you step on the brake pedal too hard while bleeding the system, the proportioning valve will be pushed to a side, which then blocks brake fluid from going into either the front or rear. to correct this, youll have to bleed the side that the valve is not blocking till the valve sets back to the center again.

try to bleed it again, if it doesnt fix the problem, itll most likely be the mc.

hope that helped.

[misnomer]

Oooh, update. . . I'm leaking out of my drivers side rear caliper, comes out in the rubber seal around the piston. Anything to be done aside from replace the caliper? Should I just do both calipers while I'm at it? Anybody have some stock rear calipers they'll sell me dirt cheap? :-)

[96twofourty]

Oooh, update. . . I'm leaking out of my drivers side rear caliper, comes out in the rubber seal around the piston. Anything to be done aside from replace the caliper? Should I just do both calipers while I'm at it? Anybody have some stock rear calipers they'll sell me dirt cheap? :-)
You need to get then rebuilt. Mosr places will be hesitant to do this because of the liability

[thx247]

not hard to find rear calipers on zilvia....I've gone through one already in a couple hundred miles

[misnomer]

Is there any reason to replace both calipers? The passenger side still seems to be in good shape. . .

<edit>

Oh yeah, and where the cheese can you get Brembo BLANKS for a decent price? Everywhere I see is crossdrilled and/or slotted. . .

[thx247]

Nopi iirc has blanks

[cdlong]

rebuilding the caliper yourself is easy, just get a seal kit from a parts store. you should only have to replace the rollback seal (square seal inside caliper) and dust seal (visible boot). it might take a while cause the seals are a little bit tough to get to seat properly but it's not bad.

you don't need to replace both calipers. if you replace pads or rotors you should do it in pairs, anything else is fine to do alone.