Breaks have a mind of their own! Help!

[huyatgr]

I have had my 1988 325i convertible for about a year and have loved driving it. But recently it has become a little scary as the brakes are completely unpredictacle. At times the car slows as normal when i press the brake pedal and other times the pedal goes straight to the floor with no resistance and the car doesnt slow down til I stamp on the pedal with all my strength. I have had a mechanic check the pads, they are fine. He bled them today and when the brakes engage they are more responsive but they don't always engage. I live on a small island so BMW specialists are pretty scarce so i would be grateful for any suggestions. Thanks

[brettski]

Could be an issue with the master cylinder seals.

[Jack Dabsy]

As Brett says...
Just to add, if it is the seals at fault, you may be as well getting another Master Brake cylinder... Just as cheap as a seal kit in many cases !
Also, just have a quick look at the rear brake flexy pipes.