Originally Posted by JohnMc

I'm just not entirely sure what symptoms are being described. Little or no pedal means.. what? No pressure and the pedal goes down and down and no braking happens? Or the pedal goes down, you feel resistance and push on the pedal, but very little braking happens as a result?

The check-valve on the vac line to the brake booster got 'sticky' on mine - mostly in vey cold weather. In that case, you have no vac boost assist, and the pedal is rock hard, and it takes a LOT of pedal pressure to get any braking. That braking system is NOT set up for non-assisted braking at all.

Alternatively - it sounds like in this case you have a firm pedal, but occasionally the pedal goes further down than normal, but the brakes work 'relatively' well once you get the pedal down far enough? That could be pad knock-back on the front wheels - if you have something a bit loose (usually wheel bearings) the rotor can wobble a bit while rolling and push the pads back further than they should go (they self adjust by the rotor runout pushing them back off, plus some rebound in the rubber seals). After the first push, they're more or less back to normal, second push they work normally.