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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:/

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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.

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  • While I agree there's nothing wrong with the 2-man approach, I don't know it's "the best". It doesn't require any special equipment, however, using a vacuum source draws out most all (if not ALL) the bubbles, where the 2-man approach isn't nearly as quick, efficient, or complete. It does work, though, which makes it a valid approach.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Feb 7, 2022 at 11:51
  • @Paulster2. I don't disagree with you at all. I don't really know the best method. That's why I wrote "in my opinion". I think it's more pshycological for me. I've done 2 man for decades before I started using vacuum. I'll even do a short stint at the 2 man method after a vacuum bleed. Seems to give me some kind of assurance. I never want to lift a car for a second bleed.
    – Jupiter
    Commented Feb 7, 2022 at 16:12
  • Fair enough! :o) Depending on the vehicle, you can do the vacuum bleed without lifting the vehicle or removing the wheel ... again, definitely "vehicle dependent".
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Feb 7, 2022 at 16:32
  • Every brake master cylinder and power brake boost unit is adjusted at factory assembly for optimum brake pedal travel. Suggesting not depressing the brake pedal completely to the floor when flushing/bleeding brake fluid would imply the linkages between master cylinder to power boost and brake pedal was incorrectly adjusted by someone or a worn master. Two man flushing or bleeding - the brake pedal must be able to go to the floor otherwise something's wrong
    – F Dryer
    Commented Feb 8, 2022 at 18:44
  • Yes, in a high milage vehicle there can be something wrong. The piston traveling through a virgin territory in the cylinder can cause the piston to stick. As long as the piston travels in or close to the normal travel area there is no potential problem. And you are correct a newer master cylinder should never have this problem, and most of the time older ones won't either, but it does occasionally happen.
    – Jupiter
    Commented Feb 8, 2022 at 21:02
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I've never heard this and have used the "two man method" many times before acquiring a vacuum bleeder.

I suppose it's possible, somehow, to damage things but I don't see how routine bleeding could do so.

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