i have a 94 olds 88 royale 172k and when pressing the brake pedal the pedal goes down around 3/4 of the way down to stop. I've replaced the front pads and calipers and the rear wheel cylinders and bleed them all the way around. If i repress the pedal down it builds pressure for a split second and looses it, it wont keep any pressure so my question is, should it bleed it again, possibly getting a power bleeder or could the master cylinder be the culprit? I will adjust the rear shoes because its feels like its only stopping with the front brakes but im not sure if that will fully fix whats going on.

If you are not leaking any fluid out, then the Master Cylinder is the likely culprit. Air in brake lines usually accounts for a spongy pedal, but not one that drops like that.

Also, these cars aren't known for having the most robust of master cylinders.

When you source a replacement, remember there are 2 lengths, make sure you get a correct one. Also remember too that refurbished units don't typically last very long. I am due for #4 since april of '08.

thanks, i think its the six inch one, after during some reading im thinking its the problem to but i was wanting to double check.

With air in the lines, it may take a lot of pumping on the brake pedal, but eventually you should be able to build and hold pressure. If you are building pressure, then the pedal leaks down to the floor, it is a problem with the master cylinder.

Same problem with my '93. This will be my third master cylinder.