if you run the master cylinder dry, do you need to bench bleed?

Discussion in 'Suspension, Steering, Brake & Wheel Topics' started by 79rallysport, Jul 8, 2007.

  1. 79rallysport

    79rallysport Veteran Member

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    I was bleeding my brakes today and I ran the master cylinder dry. Do I need to bench bleed the MC now?
     
  2. tom3

    tom3 Veteran Member

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    Sometimes you can fill the cylinder, let it sit overnight, and any air will find its way up and out. Worth a try.
     
  3. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    Try gravity bleeding it....but you may be SOL.
     
  4. Knuckle Dragger

    Knuckle Dragger Administrator Staff Member Lifetime Gold Member

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    Good answer right there. Sometimes no and sometimes yes. If it was dry too long and moved too many times you could have damaged the seals. The only way to know is to try it.
     
  5. 1FstChevy

    1FstChevy Veteran Member

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    Excuse me not knowing this... but what do you mean by bench bleed? is this a fancy term for a rather common job? Also... you spoke of damaging seals if the MC is dry too long, how does this happen? and if I recently purchased a 4th Gen MC that I might be using for my new brake setup does it make a difference whether it has residual fluid in it or is completely dry?

    Thanks for the clarification...
     
  6. kik_start

    kik_start BANNED

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    From what I understand... the reason for "bench bleeding" in the first place is to get the MC level. If installed it tilts back and there are two small areas that can trap air and never get it all out.
    I would at least jack the car up high enough in the rear to get the MC level and bleed it. IMO
    I'm sure someone will tell us if I'm wrong...

    Here is an illistration where the air gets traped and can cause rust and a soft pedal.

    [​IMG]
     
    Last edited: Jul 8, 2007
  7. Knuckle Dragger

    Knuckle Dragger Administrator Staff Member Lifetime Gold Member

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    A bench bleed is just that, working the air out of the assembly on the bench. There are a couple of ways to do it. Put lines from the outputs up into the reservoir and manually activate the master until the air is gone. Or plug the ports and depress the plunger in and out until it's rock solid, or you no longer see tiny bubbles coming up from the bottom of the reservoir.

    As long as you haven't been pumping the in a feverish pace with the master dry the seals should be OK. If it's been sitting a long time of course you may have seal issues, they are just rubber.
     
  8. 1FstChevy

    1FstChevy Veteran Member

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    Alright that makes sense, perhaps people I know just don't use that term... and the master has only been removed from the T/A donor for approx. 2 months, and had brake fluid coming out of it when it was tilted at various angles, so it should be fine!

    So any particular procedures I should follow regarding the brake fluid once I have the new master and lines run?
     
  9. kik_start

    kik_start BANNED

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    Bench bleed, then bleed lines keeping the MC full at all times starting with the right rear wheel (farthest to closest).
     
  10. jayb53guy

    jayb53guy Veteran Member Gold Member

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    I have found that cracking open the line right off the master cylinder and giving it a few good pumps will get rid of some of the air that might be trapped in the MC. Then tighten them up and bleed it normally from the right rear working forward.

    Good luck--
     

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