Master cylinder bleeders: How much air pressure?

Discussion in 'Axles + Brakes' started by BigBadJohn, Oct 12, 2019.

  1. BigBadJohn

    BigBadJohn Newbie

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    How much air pressure should you apply to bleeders like this?

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  2. grampadirt

    grampadirt On MEDICARE Officially Old

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    I do mine about 15-17psi.
     
  3. Supercharged111

    Supercharged111 I'm Awesome

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    I do mine at 10psi. Instructions specify 20, but 10 seems to do the job.
     
  4. BigBadJohn

    BigBadJohn Newbie

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    So just hook them to a compressor with pressure regulator or do the bleeder units do something besides apply air pressure to the reservoir?
     
  5. grampadirt

    grampadirt On MEDICARE Officially Old

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    Pump the tank up to needed pressure and disconnect the air supply,when fluid stops coming out of the bleeder you're working on pump it up again.I suppose you could set your compressor at your desired pressure and leave it connected but that might be a chancy.Oh,you do have a pressure gauge on the new fluid resevoir,right?
     
  6. BigBadJohn

    BigBadJohn Newbie

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    I guess I could add an air pressure gauge right before the inlet of the bleeder cover. It wouldn’t be hard. I was thinking of doing a remote button connected to a 120v air solenoid. That way I could pressurize it only when I was loosening the bleeder screws while under the vehicle
     
  7. east302

    east302 I'm Awesome

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    Motive Products makes a bleeder for that master cylinder reservoir adapter using (essentially) a pump-up garden sprayer. I’ve seen where people make them from scratch. Check YouTube, but you could probably rig one together fairly easily and add a gauge to it.

    The hard part is probably going to be getting a good seal on the reservoir. 10-15 psi would probably get you by. GM’s spec is 20-25 for pressure bleeding.

    I’ve used one before and it makes flushing/bleeding so much easier. You don’t lose much pressure cracking the bleeders so there’s plenty of time before having to pump it up again.
     
  8. BigBadJohn

    BigBadJohn Newbie

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    If anyone’s interested I just bought one of these tonight. After 11% rebate and a $5 rebate they’re less than $4.

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  9. Schurkey

    Schurkey I'm Awesome

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    ABSOLUTELY NONE. You apply pressurized BRAKE FLUID to those adapters, NOT AIR.

    1. I get the sense that the original poster has never used a pressure bleeder before, and he thinks the master cylinder adapter IS the pressure bleeder.

    You pressurize the TANK that holds a BULK QUANTITY of brake fluid. The pressure in the tank forces brake fluid through the adapter into the master cylinder. You do NOT pump air through the adapter into the master.

    Some novices on "The Internet" think they can pressurize the master cylinder with air, using the fluid in the reservoir to bleed the brakes with. THIS DOES NOT WORK, and it's a great way to pump shitloads of air into the hydraulic system.

    2. Those garden-sprayer bleeders are junk. The fluid is contaminated with humidity (water) before it even gets to the master cylinder. REAL pressure bleeders use a rubber diaphragm to separate the fluid from the pressurized air. Humidity in the pressurized air never touches the fluid.

    3. A REAL pressure bleeder will accept a surprisingly high amount of pressure. I typically start with 10--15 psi, and I don't have problems until the pressure is less than 5 psi. Relieve the pressure at the master cylinder using the shut-off valve and then crack a bleeder open briefly, BEFORE removing the adapter, or it'll be messy.


    https://www.amazon.com/Pressure-Bra...keywords=Brake+bleeder&qid=1571697700&sr=8-10
    But be sure you're getting the adapters you're actually going to need. They've changed what's included with the pressure tank since I bought mine years ago.
     
    Last edited: Oct 21, 2019
  10. Supercharged111

    Supercharged111 I'm Awesome

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    I've been using a Motive garden sprayer type since 2014 at 10psi with flawless results. I only use the fluid in the reservoir because supposedly pumping fluid from the sprayer puts more air in the fluid. I'm a road racer, so I have to trust my brakes with my life and this has been doing the trick just fine.
     

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