98 Mustang

Brake pedal would go all the way to the floor. I changed master cylnder and bled the brakes and stillvery littlepedal pressure. Could the power brake booster be bad? How often do they go out and what would symptoms would i see?

 

It sounds to me like you have air in the system.If you have ABS it's a whole other can of worms,and not live worms either,long dead stinkin' worms.
Try a pressure bleeder and force brake fluidup through the caliper into the master cylinder.It's easier to let the bubbles float their way to the master cylinder than to try to drag stubborn bubbles down to the brake cylinder.
A very small amount of air in the brake system is enough to cause the pedal to go to the floor.A bad booster will make the power assist part not work and the you will have to push quite hard on the pedal to get the brakes to apply.

 

OK, got the master cylnder changed, and a leaking right rear caliper. But when bleeding the rear brakes, you get very little fluid, and with almost no pressure. Didn't have time to check the front. Swing shift sucks. Could the proportioning valve be screwing up? Not sure where to check now. What could cause very little fluid, and pressureat theback calipers?

 

ttt

 

There still must be air in the system.You won't get good pressure until ALL the air is out.

 

I had a problem simular to this on my C-10 p/u, one of the rear wheel cyclenders went bad, but STUPID me thought it was the master cyclender, Well after replacing the MC I noticed the fluid on the rear break plate, AHH now this makes sence... lol.

Here is where it got weird, after I replaced the wheel cyclender the rear breaks would not pressurise(sp) Ihad someone pump the breaks up and the pedal would get firm but there was still no pressure to the rear breaks. WTF,, Then I had the idea to bleed the front breaks even though there was no problem with them.

Needless to say after I blead the front breaks the rear breaks would now have pressure, why I dont know, maybe the porportioning valve was out of wack till it seen a pressure drop in the front, I dunno.
But i would suggest bleeding the front breaks and see if that returns your pressure to the rear.

I hope this helps, if not it was free.... good luck.

EDIT: on a side note if the booster was bad the pedal would still be firm and you would have pressure to the breaks, they problem you would see if the booster was bad is that the breaks would not have any power assist, and possibly rough idle from a vacuum leak if they are vacuum assited breaks.

 

It almost sound slike you have a seized slide somewhere. Basically, one of your calipers cannot slide like its supposed to. When you step on the brake pedal, the caliper piston comes out and makes the brake pad contact the rotor, when it does this it is supposed to make the whole caliper assembly slide over so the other pad makes contact as well. When the slides are seized, only 1 of the pads will make contact and the caliper cant slide. Eventually whatll happen is when the 1 pad that was making contact starts to wear out, the piston will have to come out more and more each time causing the brake pedal to go lower and lower. Eventually causing you to lose pressure all together. So check your brakes clean and lube the slides. Then try rebleeding.
-P.
PS: If your booster was bad your brake pedal would be VERY difficult to push and you'd more than likly hear a hissing noise.