I've been told that if you use the 2-man method for bleeding brakes (one man at the bleed valve with a PVC tube over the nipple, one pumping pedal) you can damage the seals as "the brake shaft goes further than it's intended". They went on to say you should never press the brake pedal all the way down to the floor when the bleed valve is open on one of the calipers using this method.
I don't know what they mean but has anyone heard this? They advise only ever use the vacuum method. Weird cos half of youtube is bleeding with 2 man method:/
In my opinion the 2 man method is the best. There is validity to the "shaft" concern. The shaft would be the master cylinder piston. It has a normal use area. If you press the pedal all the way down you are using the cylinder in an area that can cause friction possibly causing it to become stuck. The remedy for this is to put a piece of 2X4 wood block or something similar under the brake pedal. This will prevent the brake pedal man from putting the pedal all the way to the floor. It will keep the pedal approximately 1.5" from the floor when pushed in.