Erratic idle when pumping brakes

Discussion in 'Technical' started by Hellsheep, Sep 3, 2016.

  1. East Coast Z

    East Coast Z Well-Known Member

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    "Could it be something else downstream of the booster however and not the booster itself?"
    Unlikely.
    Do you want to eliminate the brake booster as a possible source of vacuum leakage prior to removing/replacing it? :confused:
    Test it with a hand operated vacuum pump (Mityvac). ;)
     
  2. Hellsheep

    Hellsheep Administrator Staff Member

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    I'd love to do this; I'm assuming something basic like this would work: https://www.amazon.com/Mityvac-MV8000-Automotive-Test-Bleeding/dp/B00265M9SS

    I'd disconnect the vacuum hose and keep it connected to the booster, put pump on it and off I go?
     
  3. East Coast Z

    East Coast Z Well-Known Member

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    That's it!
    Yes, that's all you'd need to do.
    If the booster maintains vacuum, it's OK.
    If vacuum can't be achieved, or disappears quickly, you have a leak.
    Those vacuum hand pumps are a handy item to have in your toolkit.
    Some of the Mityvac's are a vacuum/pressure pump design.
     
  4. Hellsheep

    Hellsheep Administrator Staff Member

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    I completely agree it'd be useful! Especially for the brake bleeding capabilities of it also.

    I'll get one ordered and test it out when it arrives :) You are a legend and always a wealth of knowledge! Thanks
     
  5. SrAfciGeR

    SrAfciGeR Member

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    Well there is nothing downstream of the booster if you unplugged the line of the booster it self and plugged it there.

    Sorry to say but it looks like booster replacement jobie...
     
  6. rob260

    rob260 Moderator Staff Member

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    As above there's nothing downstream of the booster -the good news is they are not horrendously expensive nor too hard to change. You will probably find your brakes remarkably improved once you fit a new one, too.
     
  7. Hellsheep

    Hellsheep Administrator Staff Member

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    Cheers guys, good to know. Best place to get a booster if I end up needing one brand new?

    Also I need to get new rotors as it looks like the front two are factory, warped and probably well below the safe wear margins.

    I was looking at some DBA rotors, car is only used for street use, any idea what I can get? it's a 1990 NA with 26mm rotors (tested fitting my TT rotors but they are definitely too big that's how I know they're 26's not 30's like post 91's)
     
  8. CHILI

    CHILI Indestructable Target

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    Best value is DBA 4000 Series Discs...Like they say "If you have a $10 Head, buy a $10 Helmet".:zlove::br:
     
  9. Hellsheep

    Hellsheep Administrator Staff Member

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    I looked at these but the only ones I can find are 30mm thick which won't let me fit the NA calipers on the front.
     
  10. rob260

    rob260 Moderator Staff Member

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    Try contacting Brakes Direct http://www.brakesdirect.com.au about rotors; they are good supporters of the forum.

    I can supply a booster if you need.
     
  11. Hellsheep

    Hellsheep Administrator Staff Member

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    Sweet they were excellent. Ordered some rotors with them.

    I'll likely get a new booster down the track but since I still have a Zed sitting at home doing nothing im trying to take off its booster to throw it in as it looks fairly new so hoping it'll get me by until I can order one from you. However I've managed to unbolt it, disconnect from the pedal and removed the master cylinder from it, how do I get the darn thing out? There isn't enough room it seems to get the linkage Bar through the firewall.
     
  12. rob260

    rob260 Moderator Staff Member

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    It should fit -keep jiggling!
     
  13. Hellsheep

    Hellsheep Administrator Staff Member

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    Haha I'll have to pull a bunch of hoses and also move some wiring I think. There is custom hoses for some weird JDM thing the previous owner did. He made it so when you spray water on the windscreen it also sprays water on the intercoolers by using some hose and some t joins off the windscreen washer hoses running down to the side mounts with a little sprinkler head plugged in the end... Those hoses look like they are in the way as well as some wiring
     
  14. Hellsheep

    Hellsheep Administrator Staff Member

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    Well on the weekend I managed to swap the booster as a test with my 300zx, before bolting it all up I tested it and had the same issue when pumping at idle. Figured I'd wait for my mityvac but suspected both boosters are bad.

    Tested both boosters today with the mityvac, first I tested by blocking the rubber hose with my finger and the other side connected to the mityvac, good vacuum and it can maintain it so no leaks there. I was using good rubber hose as a test however. Found one of the boosters hoses is dodgy and leaks, so I'll replace that. The other hose is okay but is very hard and I suspect I may as well replace it as well.

    Upon testing both boosters with the mityvac it confirmed that no vacuum pressure was being maintained at all. I could slightly build up some by pumping over and over with one booster, the other booster however had no vacuum pressure at all. Time to order a new booster.
     
  15. Buckaroo Banzai

    Buckaroo Banzai New Member

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    If you haven't fixed the problem yet try replacing your battery with a new or known strong one. I know is sounds crazy but I had an issue with my Z that was similar. It would drive and stop fine but when coming to a slow stop the last foot of the stop or so the pedal would go to the floor. I replaced my brake master cylinder, bled the abs unit, bled the system multiple times and even paid a shop to bleed it and it still did it. Then I found a note in one of my manuals that said a low battery could cause a low speed issue with the abs module. I put a fresh battery in and it went away. Fixed my brakes with new battery, crazy.
     
  16. AndyZ32

    AndyZ32 Member

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    Would you not have had the ABS warning light showing? Not sure myself, just interested to know. In which case checking that the bulb and the ABS fuse are ok then running through the diagnostics in the FSM section BR page 38. But yeah thats one of the oddest things I've ever heard.:confused:
     
  17. Hellsheep

    Hellsheep Administrator Staff Member

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    Definitely quite an odd issue you had there, my battery is pretty well brand new so I don't think it's my issue and I've confirmed that the boosters I have can't keep vacuum pressure so likely a split diaphragm in both of them.
     
  18. Fists

    Fists Well-Known Member

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    Wow, you're pretty unlucky to get two busted boosters, don't hear of them failing too often in the Zs.
     
  19. Buckaroo Banzai

    Buckaroo Banzai New Member

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    I didn't have any warning lights. It was really bizarre. It stopped just fine when stopping hard, the only time it ever did it was at a slow stop with the engine at idle and in neutral if I let up on the brakes a little and reapplied them. Straight to the floor and then stopped after another foot or so. Anyhow, not to thread jack I just wanted to throw it out there in case that was the issue. It took me so long to finally sort it. I actually registered specifically to share in case there was someone on the other side of the globe banging their head against a wall like I was.
     
  20. Buckaroo Banzai

    Buckaroo Banzai New Member

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    Just thought I would throw it out there since it was so bizarre it might not get checked. If it persists after the booster replacement you may want to check your alternator output as well. Mine went shortly after the whole ordeal and I wouldn't be surprised if an old batter in conjunction with an alternator barely charging caused the problem when at idle. Hope you get it sorted.
     

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