Old soft hoses will also add to this squishy feeling. One thing, when bleeding the brakes on a system that is getting up there in years DO NOT PUSH THE BRAKE PEDAL ALL THE WAY TO THE FLOOR when the bleeder is opened. Any corrosion that is present in the master cylinder will damage the seals as the piston goes further than it has ever done before ripping the seals. You can get away with this on a new one but not an old one.
The best method is to use a vacumn gun and have someone keep the master cylinder at least half way full and to pour gently. Pour it from high up and you get air bubbles in there that you just end up pulling thru the system in an endless loop. Eastwood has a one man bleeder system and the filler bottle goes in upside down into the master cylinder resevoir with a float valve in it, as the level goes down it allows more fluid to drain out of the bottle and into the resevoir. The eastwood one has changed is is now pressurized, not sure whether I like that or not, you need an exra mastercylinder cap with a hole drilled thru it to put on a fitting.
My friend did a brake job on a ford aerostar that has ABS a couple of weeks ago. He put a new master in and had a heck of time getting all the air out. It took 7 bleeds with the bleed machine to get all the air out. Air was collecting in the high spots on the abs assembly, only a concerted continous bleed got it all out at what he swears was 'A bubble at a time it seemed like'... and this was doing all 4 corners at the same time....
