Z32 Weird Power Brakes

Discussion in 'Technical' started by Neddey, Oct 20, 2020.

  1. Neddey

    Neddey Member

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    My 1993 2+2 TT auto has done a bit of hibernating over recent months, as have many of us. I run it every 3 or 4 weeks and give it some road exercise every month or so. Yesterday I took it out for some road work and the brakes acted very strangely. When I applied the brakes steadily just to slow down, the power unit applied them very hard then very slowly the pedal lifted back to normal. In the end I was helping the pedal back myself by putting my foot under it and lifting. Thirty minute drive, no change. All technically competent opinions on the cause, and the fix will be greatly appreciated.
     
  2. NI85

    NI85 Member

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    Whilst not the most technical opinion. If you have to lift the pedal up with your foot. It appears you have air in the system. Check your fluid level if you haven't already done so.
    Also as your car has been hibernating. It might be also good to flush and replace the brake fluid.
     
  3. beaver

    beaver southern zeds

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    Here's a simple test. With the motor not running apply the brakes 5 times and wait one
    minute. Then apply the brakes as normal holding your foot on the pedal. Now start the engine.
    If the booster is working properly, the brake pedal will sink a little as the booster applies extra
    pressure. Now turn the engine off. Your brake pedal should stay down. If your pedal slowly
    comes back, you have a vacuum leak. cut from power brakes south/au. check it out.
     
  4. Martin Williams

    Martin Williams Well-Known Member

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    I'm no expert but you should never have to use your foot to raise brake pedal it is spring assisted. In my opinion you have a problem in you brake master cylinder, probably needs needs reservoir cleaned out and new set of seals.
     
  5. zx299

    zx299 Well-Known Member

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    I agree with MW. The brake fluid is bleeding past the MC seals :eek: .... time for an overhaul :cool:

    I suggested putting a kit in your cylinder because the cost of a new MC from Nissan is prohibitively expensive :mad:
     
  6. Neddey

    Neddey Member

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    Thanks, tested as described and vacuum seems ok.
     
  7. Neddey

    Neddey Member

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    Where is most likely place to buy brake master cylinder kit?
     
  8. rob260

    rob260 Moderator Staff Member

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  9. Neddey

    Neddey Member

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    Hi Rob, long time no hear. I only want the kit and am having some trouble finding one. Do you know what the ID of the cylinder bore is or how you can tell from the letters / numbers on it, and also what other Nissan vehicles used the same cylinder (Skyline, Sylvia, etc)?
    cheers
    Terry
     
  10. IB

    IB ?????

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    Your master cylinder is most likely pitted causing the leak past the seals. If you want to rebuild it then getting it sleeved would be best.
    For the price of the one Rob linked to, it might be a better option.
     
  11. Neddey

    Neddey Member

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    While getting ready to remove the MS I moved one of the silicone hoses that are near the cylinder to get access and it (too easily) came loose in my hand so was either already broken or severely cracked. The hose connects vacuum from the balance tube to a device (see attached pic) on the drivers side of the engine bay, and almost certainly would have caused a vacuum leak. What is the purpose of that device and could the vacuum leak have caused the weird brake problem – I have already “sucked” the fluid from the reservoir and loosened the bolts and tubes so don’t feel like putting it back together if the broken tube has no effect.
     

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  12. NI85

    NI85 Member

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    That little box is the car's standard boost gauge sender unit
     
  13. Neddey

    Neddey Member

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    Thanks
     
  14. Martin Williams

    Martin Williams Well-Known Member

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    Will not give you the effect of brake pedal not returning.
     
  15. Neddey

    Neddey Member

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    Got the MS out and it has already been sleeved, so no pitting that I can see, but haven't got the front piston out yet (diff post). Source of problem fairly clear, small semi-soft lumps of gunk in the fluid coming out of the MS would easily have at least partially or temporarily blocked one of the cylinder outlet ports.
     
  16. beaver

    beaver southern zeds

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    The price to rebuild my master cylinder was $270 s/s sleeved. I remember thinking buy a new one this is a ripoff, and i should have listened tms, because its now weeping under the res.
     

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