You need to pick up a shop manual. You gotta brake booster buddy. It's hard to stop without it. Actually, my diagnosis is pits in your master cylinder, or faulty brake tube or hoses. If these are not sound, the booster can't help like it should....
Don't know if you have done this, but an inspection of the tubing and hoses on an old truck is well worth the time. My '48 2-ton was parked when I bought due to "brake problems." I looked at tube full of pinhole rust, then carefully removed, labelled each piece, and then bent new clones from new tube. If the hoses have any checks or cracks, it's time to replace with fresh stock. Just my two cents, or would you rather eat the Lexus?
