Brake Peddle soft/bad brakes

So my 1996 thunderbird is exhibiting brake failure.

The booster is original, the MC is not (about 10 years old). 

When vacuum is not applied I have little to no brakes until the end of pedal travel, no resistance in the pedal either.

 Once vacuum is applied i have a slightly stiffer pedal, but it still slowly travels to the floor, pumping it gets a bit more feeling but it still leaks down to the floor. 

I do have a leaking front caliper that is weeping fluid when I try to use the brakes and it's obvious after a test drive that the rotor is not getting scuffed or pressure to it.

so, 

 MC bad?  

Booster Bad?

Just replace teh caliper and pray?

Just replace the old nasty fluid and try it again?

I'd replace the caliper, bleed it and try again.  That will at least make it easier to find the problem, as you'll be getting one known problem out of the mix.  

You need to start by replacing the leaky caliper.  If fluid is leaking out then there's a good chance that air is leaking in.  Also, driving around with known defective brake parts is, um, let's just say, not the best idea.

If the pedal is going to the floor because of a leaky caliper, you'd have fluid running down the caliper.  

If the caliper is weeping, replace the calipers (both) and the master (because of the sinking pedal)

What the guys above said, all of it.

I am utterly perplexed that the pedal is firmer with vacuum, unless I'm misunderstanding you.

That said, as has been touched on, not much point in trying to troubleshoot weird behavior on a system that has known problems.

When diagnosing a problem, ALWAYS fix the known issue(s) first.

Like mentioned, the leaking caliper alone could cause pedal drop, especially when you factor in that it could/probably is sucking air in to the system.  Waiting on replacing the MC is only gambling fluid and extra time bleeding the system again if you didn't want to do all at the same time.

So seems like a consensus that the booster is not the issue. 

I get NO pedal feel until the floor w/o vacuum.

With vacuum I get some pedal feel.  

I have never driven teh car as is, I bought it back for $400 dollars.  Owner had been driving it for months this way...  (see my mn12 build thread.)  I trailered it home and parked it.  

Anything leaking should be replaced and the master cylinder is always a suspect. I think the master wears faster than the other cylinders since it moves a lot more. 

Even if the caliper wasn't leaking, it needs to be serviced because it's not clamping the pads against the rotor.  Start there and see where that leads us.

I'd rebuild all the calipers, replace the master, and replace the old rubber hoses.

Brakes are relatively cheap for what they do.  

when I had the car 3 years ago all the rubber brake lines were replaced, as were the pads and the rotors. 

I did a fluid flush then but the brakes were never "right".  

ordered all but the MC and I need to go to the JY to get the mustang calipers that are an upgrade to the car. 

Mad_Ratel said:

So seems like a consensus that the booster is not the issue. 

I get NO pedal feel until the floor w/o vacuum.

With vacuum I get some pedal feel.  

 

I have never driven teh car as is, I bought it back for $400 dollars.  Owner had been driving it for months this way...  (see my mn12 build thread.)  I trailered it home and parked it.  

So, engine running, pedal is ok, engine off, the pedal goes to the floor?  That is backwards, unless you have a hydroboost system.  They get pretty weird when there is air in the power steering fluid.

pedal goes to the floor at ALL TIMES.

with vacuum it just goes to teh floor slower.  (i can feel some resistance about 3/4 of teh travel).  

Resistance felt under power braking, maybe it's just the piston in the bad master moving faster and sealing a bit better? I've had a failing clutch master act that way, pumped back up quicker if you were a bit abusive with the pedal. 

In any event, pedal to the floor and not pumping out a proportionate amount of fluid somewhere on the ground from a blown line or whatever is always a bad master unless there's a ton of air in the system for some reason. 

Repair obvious leaks, bleed system thoroughly, check for pedal creep.  Recheck for leaks, now under pressure.  Repair.  If it still creeps, renew master cylinder.

I would put a master and new calipers on it with out going any further.