Outer Limits 4x4 Board

My breaks on the troopy are starting to give me trouble. when im at the lights waiting for green the brake peddle slowly sinks toward the floor, and i have to pump it a few times before pulling up Any one know what my problem is?

details.....
1984 HJ troopcarrier
Disk front
Drum rear
cant see any leaking fluid anywhere and fluid level hasnt dropped either.

thanks

If you havnt had any brake work done lately, its more than likely worn seals in the m/cyl bleeding back into the reservoir.

Try bleeding the brakes might have gotten air in them.