brakes, master cylinder, I am frustrated!!

I am trying to get the brakes working good again on my '89 chevy k1500. I have gone through two autozone master cylinders now along with one napa one (re-man'd) and the pedal is still going to the floor. My dad made the mistake tonight of pushing the MC all the way in when bench bleeding it, which the instructions say not to do. (I didn't do that on the first two!!) My question is why not? I measured the distance the pedal pushes it in and that is the exact same as how far it is possible to push it in when its on the bench, so what gives? I wonder if that is the problem with my reman'd napa this time around? The only thing I can think of is when you push it all the way in the seals are getting torn up, is there any insight into my problem? I bled the heck out of the lines and its not leaking fluid, whats the problem?

My best guess would be that the MC has two seperate pistons that are seperated and acuated by fluid . The front may be designed to operate first and the pressure in the MC pushes to the back end . Just a hunch . Rob

You can test the master cylinder by plugging the outputs with a plug. If your pedal is solid with the plugs in there, then move down the system. Remember, air is very easy to compress, so all of the air needs to be out of the system before you will get a firm pedal. Also, the rear brakes need to be adjusted so there is a slight drag on the drum when turned by hand. If they are not adjusted correctly you will not get a firm pedal. I just went through this on my 90 c1500. You wouldn't believe the difference a small adjustment to the rear brakes will make in pedal feel.

Rmbodie - are you implying that possibly I am having MC issues?

dewaynep - I will try capping it and see if that tells me anything. What doesn't make sense is it is not leaking fluid, and if it was air in the lines, with repetitive pumping while trying to stop the brakes should get slightly better
right? I bled the heck out of the lines and wasn't getting any air. Have you guys seen alot of cheap/crappy/faulty MC's out there?

What else is new in this setup? Just the MC? You mentioned that this is the third one. Did you have the same problems with the other two?

When you bleed the brake system are you doing it in this order, right rear, left rear, right front, left front?

is it just you bleeding the brakes or do you have someone to help you?
Typically if you do it by yourself, after you pump the brakes then run to the MC the preasure is almost gone. YOu need some to pump then you release.