And another thing, if the rear brakes are drum type, after you work on them you need to manually set the adjusters so the shoes almost touch the drum. If they are real slack you will have excessive pedal travel, though I think the car would still stop.

 

bad booster will cause a stiff pedal since theres no brake-asist(similar to power steering, power steering=easy turning, no power steering=little more difficult). if u've ever drivenon the road andshut the car off, hit the brakesand after a couple presses itbecomes very stiff andto the point wherethe brakes are useless, u'll know what im talking about...a faulty master cylinder will usually hold pressure on the pedal when pressed and while still holding, butthe pedal will begin to sink slowly.

more detail of exactly whats happening and when it happens would be helpful.