Odd brake problem

[Smitty1021]

So I've seen a lot of threads regarding spongy brakes but I have an issue I've yet to see possible solutions too, unless I've missed it. I had spongy brakes and replaced my MC twice, drivers side caliper (passenger is only year and a half old) and bled my brakes using different methods many times and I have has a huge improvement but I'm still left with a brake pedal that one day catches right at the top and is extremely firm and works very well to the next day sinks all the way to the floor before it catches. The brakes are always different every time I drive the truck and its from one extreme to another. Any idea as too what it could be?

 

[VorTecxas]

Try the check valve that is plugged in to the front of the booster, it's the plastic nipple that the vac hose runs to. I had a similar problem and that was all it was

 

[twomanymontes]

I'm sure you probably have checked this, but check the wheel bearings for play.

If the bearing is loose, more than 1/4" play, the rotor will wobble and you will get a low pedal. When the rotor wobbles the other way the pedal will return.

Don't know if you have ABS or not, but there may be air trapped in the valving.

Hope this helps

 

[Smitty1021]

I checked the valve on the front of the brake booster and it doesn't seem to have any leaks. Rear wheel bearing and front hub bearing assembly is brand new too. I had a abs light on for years but once I replaced the hub bearing assembly with the internal sensors, the light turned off. Wouldn't air bleed out of the abs valving after so many times of bleeding the brakes or am I wrong? Should it be bled at the lines running into the module itself?