Overcomplicated brake bleeding

Discussion in 'Z32 Technical' started by Cliff, Feb 1, 2019.

  1. Cliff

    Cliff Member

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    So to overcomplicate a simple task, I have replaced my master cylinder and now need to bleed the brakes.

    Yes, i know the FSM states the order as:
    Left rear
    Right rear
    Left front
    Right front
    ABS front
    ABS rear

    I pretty much always follow fsm HOWEVER; when analyzing the brake line schematics in the FSM it seems like a no brainer that the ABS lines should be bled first to avoid pushing air from the master cylinder change through the entire system.

    Screenshot_20190131-120807_Drive.jpg

    For example:

    1. I now have air in between new BMC and ABS actuator.

    2. I will put in new fluid and bleed to remove air.

    3. Both front and rear lines from the BMC go directly to the ABS actuator, thus bleeding from ABS front and ABS rear would remove the air in line before going to all 4 wheels.

    I trust the thought and wisdom the Nissan engineers put into the Z so I've got to be missing something important here. I'd love to hear some other thoughts on the matter.

    FWIW I will still follow the fsm procedures this time around because God knows our Z's can be temperamental, but due to the quirkiness of what is typically a basic maintenance job, I wanted to draw on the thoughts of others.
     
  2. zx299

    zx299 Well-Known Member

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    Air bubbles rise in the brake fluid, so they will accumulate in the actuators (being a high point), that's why its left till last

    When you bleed each point, continue bleeding until you see fresh fluid. You want to get all the air out, but you also want to purge your system of ALL your old fluid :cool:
     
  3. Shane001

    Shane001 Well-Known Member

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    If you do ABS first you'll still need to do it last as well.

    With a new BMC I'd be repeating the cycle through a couple of times. Also again after having a good run.
     
  4. East Coast Z

    East Coast Z Well-Known Member

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    Did you bleed the Master Cylinder on the bench prior to installation?
    This practice would lessen the amount of air you would introduce into the system.
     
  5. KEZA

    KEZA Zed Fiend

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    Another option is to use a length of plastic tubing that will fit over the bleed nipples tightly, make sure you have enough length to run the other end of the tube to your Brake Master Cylinder, this is required to ensure all air is expelled
    from the system.
    Ensure that you clip the tube just above the BMC end, and just above the fluid level.
    Once the tube is in place, crack open the nipple and pump the Brake Pedal until all air is removed from the line.
    Repeat this process on all wheels and required sections according to the Manual Instructions.
    The only thing you have to watch is that you top up the BMC after each time you each bleed point or as required, this depends on how much air is in the system. Hope this helps.
    Cheers
    Keza
     
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  6. zx299

    zx299 Well-Known Member

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    Geez, talk about 'overcomplicating' brake bleeding :eek:

    3 metres of tubing to pump the sh@tty old brake fluid back into your master cylinder again :rolleyes:

    What's wrong with 40cms of clear tubing and a Vegemite jar ? This method has worked well ever since brakes went hydraulic ....... you purge the air out of the system AND you dump your crappy old brake fluid :cool:
     
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  7. Shane001

    Shane001 Well-Known Member

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    Also running a tube back to the BMC is essentially aerating all the fresh new fluid. Not a good idea. (Sorry Keza!)
     
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  8. beaver

    beaver southern zeds

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    As zx299 says dont dump the old fluid back into the bmc, Ive bleed the abs on my car plenty, taking the car out for a run in between bleedings is a the way to go, you want to cycle the abs to get all the air out. I used a long plastic tube from the abs to the ground out side the car and made sure the bottle I used had a screw on lid with a hole pocked through it, then put the plastic hose through the hole in the lid and added few inches of fluid. The tube should never be above the fluid in the bottle or its going to suck air.. skimmed keza's thread.. woops
     
  9. ADAMZX

    ADAMZX 2000spec Conversion

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    I'm soon to bleed my brake system on my car and I'm using a tool called a power bleeder

    [​IMG]

    basically you connect the power bleeder to the master cylinder and then hand pump the bleeder to 15 psi which will pressurise the brake system just like when you have depressed the brake pedal. All i need to do then is connect fluid catch bottles to each of the brake bleeder valves on each caliper in the proper order and the old brake fluid will be pushed out and replaced with new fluid from the power bladder.

    it will make all future brake bleeding jobs for me super easy and I can also check the brake hoses for leaks when the system is pressurised.
     
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  10. Shane001

    Shane001 Well-Known Member

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    ADAMZX I have one of those also, makes the job so much easier.

    Tip. If doing a full flush, don't push any fresh fluid in initially, just pressurise it and bleed out each nipple until you get air, then put in the fresh fluid. So bleed out all the old fluid first. Sometimes it's hard to tell when the old stuff has passed and the new stuff is now bleeding off.

    When bleeding with new fluid just make sure to keep an eye on the level in the MC and keep it topped up.
     
  11. KEZA

    KEZA Zed Fiend

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    One would expect that if you were bleeding the system after replacing the BMC, any sane person would be using New Fluid. But then we can't expect that everybody is sane, can we. :)
    I have not seen the device that Adamzx mentions, but it would be easier by all accounts I agree.
    Some of us Old Buggers don't keep up with new tech specs. :)
    The one thing I am pleased about, is the number of members that have answered this post.
    I was beginning to think that this had become a Ghost Site. :):):)
    Cheers
    Keza
     
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  12. KEZA

    KEZA Zed Fiend

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    Read what I stated again Shane. The tube is placed above the fluid level, thus not putting air back into the system. And after replacing the BMC, most sensible people would be using New Fluid.
    It's not Rocket Science. ;):):)
     
  13. Cliff

    Cliff Member

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    Wow, thanks for all the interest here guys!

    I did go ahead and follow the fsm procedures and the brakes are solid once again. I bench bled the master cylinder while it was installed on the car like so:

    1. Mount BMC on the 2 bolts coming from brake booster.
    2. Dont connect brake lines
    3. Screw in 2 bleeder screws ($8.99 for a various sizes set at auto store)
    4. Use 2 clear hoses to connect the new bleeder screws to the BMC reservoir.
    5. Fill reservoir with new fluid.
    6. Make sure the clear hoses are completely submerged in the new fluid.
    Pump brake until no more bubbles are present.

    I initially had a firm brake after bleeding but then I drove it around the block and it got squishy again. Went home and did another round of bleeding and all is well.
     
  14. ADAMZX

    ADAMZX 2000spec Conversion

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    Unfortunately my experience was the complete opposite. let the bmc run dry bleed the system 8 times over 1 and a half days period before giving up with a spongy brake pedal. my dad then informed me we needed to bench bleed the bmc which I had never done before or anticipated and so my dad spent another full day of bleeding the the whole brake system before it finally all the air was removed from the system.

    it was one of the worst weekends I've had working on the z in a while. I'm greatful it's finally over but one word of advice if your not removing the bmc don't ever ever let it run empty.
     
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