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Brake peddle hard, does not brake

Hi folks. I have a 86 7.3. I have 2 issues one minor the other dangerous. The latter first. Driving down the road and trying to stop. The peddle is somewhat soft for about 2 inches and then gets hard with no breaking power. Oh it stops but not as it should. I cannot lock the wheels at all making this a dangerous situation.
The minor problem is the fuel filter assembly. There is a valve at the bottom of the assembly and that little O ring is not to be found. Does anyone know where I can find one. I tried the Ford dealer, pneumatic shops and they do not have any this small. You can see where they, at one point, even reversed the O ring to temporarily fix the leak.

Please give me a clue as to how the poor brake performance and fuel filter assembly are related. I suspect your brake booster is not getting vacuum but I was wrong once so don’t count on it.

I’ll start with the brakes. New booster, bled the lines and I know about the slave in front, that’s been changed also. Clue, when driving and need to stop, I can put all my weight on the peddle and all you feel is a slight breaking pressure and will take 3 times the distance to stop. The vac pump is new. Although you cannot hear a vac leak, I am not ruling out the all the line hoses might have to be changed, but I might be missing something. On the leak its the O ring that’s bad. It does need to be fixed as it drops fuel on the manifold.

Have you verified that there is vacuum at the booster check valve?

When I remove the booster hose and put to my thumb, the suction pressure is enough to hold the the hose to my thumb without having to hold the hose.

RE: O ring;
Try an HVAC, air conditioner supply/dealer. They sometimes have small O rings which may hold up to fuel ?

Then apparently you have the needed vacuum. With the parking brake set and the engine running listen under the dash while applying pressure to the brake pedal. If you hear the whislte of air leaking your booster is bad.

Good idea. Did not think of that. Thank you will do.

For the o-ring, in my area there’s a place that specializes in vehicle fuel system problems. If anybody had that part, they would. Something like that may not be possible to find a source for though. But look in your yellow pages for a fuel system specialty shop or business. Like those little crush gaskets an the underside spark plugs, ever tried to buy one of those? I’ve never found a source.

OP stated “I have 2 issues”. They are therefore not related.

Not to be smart but I used to peddle insurance but press the brake pedal to stop the car. Could it be glazed pads if the power assist is ok?

Severely glazed brakes haven’t shown up here for quite a while @Bing. I had though the ceramic and metalic pads were somewhat immune to galzing.

For O-rings:

Yeah that looks like a good source but have make sure you do a precise inside and outside measurement metric and SAE. Seems to me I ordered some O rings from them for a nail gun rebuild a few years ago.