I'm having a big problem with my brakes. The pedal is soft/squishy, and slowly sinks to the floor.
What I've read on the internet is that soft/squishy brakes is usually caused by air in the lines. But a pedal that sinks to the floor is caused by a bad master cylinder or a leak.
I am using the 4 stock mustang calipers that came off my donor 1996 GT. It has two piston PBR's in the front. This spring I bought powerstop Z26 pads, which are supposed to have higher friction. I thought they might be better than the stock pads I bought at auto zone when I built the car 10 years ago.
First problem. I could not retract/turn the rear caliper pistons into the calipers, probably because they were 30 years old. I bought 2 new rear calipers at autozone. I added new DOT 3 brake fluid (that I bought last month) ,and bled all four calipers. I was careful not to let the fluid level in the reservoir get too low. I "adjusted" for the parking brake by pulling the lever about 10 times (which is how I've read you're supposed to adjust it.) I could not get a firm pedal, and it would sink to the floor.
My research on the internet led me to believe that the master cylinder had an internal leak. I purchased a new Dorman master cylinder (M39637 for an 87-93 mustang), which is what factory five told me to use when I first built the car. I bench bled the MC, following the instructions in the box, installed it, then bled all four calipers. No change; it's still soft, and sinks to the floor.
I don't see any fluid leaks. there are no bubbles when I bleed the brakes. I've used almost a full quart of new brake fluid.
What am I missing? Could the new rear calipers or the new MC be bad? Could there be something wrong with the new carquest brand fluid?
Thanks for your input.