replaced everything(brake booster, mc, ss lines,s vacuum line, pads rotors, etc) no air in lines and yet very little pedal pressure, brakes dont start to grab til pedal is at floor. Can build some pressure if i pump brakes but doesnt hold.

 

sounds like you still have air in the system. bleed at each caliper until you are POSITIVE clean, airless fluid is coming out. bleed in this order: RR, LR, RF, LF. check for leaks in the process.

 

If you're sure you bled it right and enough times then the brake pedal pushrod (adjustable) being too short will cause excessive pedal travel.

 

i have the same problem
brand new brakes all around and the pedal is really soft.. sometimes it goes all the way to the floor no problem.

how do u adjust break pedal pushrod.. and im guessing its behind the pedal?

 

yeah its behind the pedal.

 

There is also an adjustable pushrod between the MC and the booster unit.
There are specs in the FSM concerning it's length.

 

Sounds like air or the wrong master cylinder or ????? Got me. Air is the first thing that comes to mind. Or one or more of the pads is installed incorrectly or ????? part of one of the brake assy is rust frozen in place? Just wild *** guesses.

 

See post number five on this thread: https://www.rx7club.com/1st-generation-specific-1979-1985-18/another-brakes-question-no-anti-rattle-spring-%3D-brakes-engaging-late-478769/

 

if the Pedal is Hard,HARD,and the Brake just don't wanna Grab,but to you they feel OK when you step on the pedal.then the Vacuum hose between the Booster and the Steel line is REVERSED(if you took it off) that little "S" shaped rubber line contains a Check Valve in it that will only Give vacuum to the Booster..not a two way valve..so If the hose is on Backwards,it hits a BRICK WALL,and since the Booster gets NO vacuum assist,it is like Very Bad Manual Brakes.

 

He has new everything for brakes. And brakes are bled correctly. I think its the check valve but someone won't listen...

 

the only parts that aren't new are the calipers, im gonna tackle this again tomorrow. Hailers, thanks for the link gave me a few ideas. Misterstyx69, kinda hard to screw that one up as the rubber line has a arrow pointing to the engine side. Dustin the check valve is fine.

 

lol its not the check valve. A bad check valve would either cause you to have no vacuum assisted braking (REALLY hard pedal) or your brakes would have a really hard pedal right after the engine is shut off with no 2-3 strokes as reserve.

 

well rear calipers need rebuilding so i get to do that, hell might as well do all 4 of them while im at it.

 

so the arrow (check valve) faces the motor?

 

yup

 

Did you properly bench bleed the master cylinder? If you didnt do it by the book, you could have ruined a new master cylinder. Calipers even when in need of a rebuild dont generally cause a soft pedal.

Its either the master cylinder wasnt bled properly, or you have air in the system. I worked at a muffler and brake hellhole for long enough to know what I am talking about.