Clutch weirdness...

Discussion in 'Technical' started by MaxxAction, Apr 1, 2016.

  1. MaxxAction

    MaxxAction New Member

    Hey everyone...

    I am having a clutch issue that I cannot pin down, and, as always, when I can't get an answer on the american boards, I look for input from my Aussie Z brothers.

    So I did the LS swap last year, very happy I did by the way, and I bought the solid fork and shortened pivot ball from Zspeed. Since then, the clutch has always engaged really close to the floor. A couple of weeks ago, out of the blue, the clutch got really inconsistent. Sometimes it felt normal, other times almost no pressure with the engine on, and having to pump the clutch to get it to disengage.

    This week I replaced the slave, and the master, flushed through with a litre of new fluid, bled it, correctly, and adjusted the clutch pedal out as far as it will go. It is better, and 19 out of 20 times I press the clutch, it will disengage fine, but that 20th one, I still have to pump the clutch a couple times to get enough movement to disengage it.

    The guy that sells the fork kit swears that the pivot ball being shorter doesn't matter, but I don't see how it can't. So I think that is part of the issue. Otherwise, I am stumped. Is there anything in the booster that can break, or wear down so motion is reduced? Anything else you guys can imagine that would cause such an issue? Thanks.
     
  2. rob260

    rob260 Administrator Staff Member

    The HD ball/fork combo isn't your issue; you need the shorter pivot being that the cast fork is thicker than the 300zx pressed fork.

    What you describe sounds like air in the line.
     
  3. Fists

    Fists Well-Known Member

    Did you ever adjust the free-play in the pedal? There isn't really anything in the booster than cause squishiness unless the front seal is busted applying vacuum to the master and pulling fluid out of it.

    Did you get a one piece clutch line too?
     
  4. MaxxAction

    MaxxAction New Member


    One piece clutch line is on the list. The pedal has to be all the way up to disengage the clutch, but there is a ton of play at the top of the pedal. With the engine off, about two inches, with the engine on, more. Like I said, weirdness.
     
  5. Fists

    Fists Well-Known Member

    You need to adjust the pedal so that there is way less free play, half your travel isn't even pressing on the master cylinder.
     
  6. Fists

    Fists Well-Known Member

    Or maybe the reaction disc managed to fall out of it's socket in the booster when you changed the master, if you have room to rotate the master out of the way without unhooking it again have a look at how the push rod sticks out of the booster at rest.
     
  7. MaxxAction

    MaxxAction New Member

    That's what I had heard about before but couldn't remember what it was. What is it made of? Does it wear out? Nothing fell out when I changed the master. at least I don't think so.
     
  8. Fists

    Fists Well-Known Member

    http://www.aus300zx.com/forum/showthread.php?t=329192 Picture 7, just a rubber spacer, don't think they wear or perish at any noticeable rate. They're only held in by being sandwiched in there between the rods and a bit of grease sticks it down, if the push rod got bumped moving the master cylinder it may have pulled it out of it's socket.
     
  9. MaxxAction

    MaxxAction New Member

    I have never read what the symptoms of a dislocated reaction disc, does anyone know?
     
  10. Fists

    Fists Well-Known Member

    It's just a spacer, symptom is you lose a bunch of effective pedal travel. There are measurements here http://www.300zx-twinturbo.com/cgi-bin/manual.cgi?list=cl&slide=12 for what the length of the input and output rods should be on the booster, if the output is sitting too far inside the booster or doesn't immediately move with the pedal then the disc fell out.
     
  11. MaxxAction

    MaxxAction New Member

    I did some reading about it all over the internet, and evidently it is more than just a spacer. It actually regulates when vacuum assist is applied. When it gets displaced, the booster is constantly applying vacuum to the mechanism, changing the throw by "pulling" the clutch pedal forwards more or less, and making the pedal feel mushy.

    I drove the car last night to go to a local car meet, and it worked fine all night, didn't grind in between shifts, felt perfectly normal. I don't get it. What can cause a clutch to work right sometimes, and not others?
     
  12. Fists

    Fists Well-Known Member

    Pretty sure that only applies to some double diaphragm units as found in brake systems, the clutch booster is simpler. If the reaction disc does any sealing in the clutch unit losing it would reduce assist not make it constant as it is between the two chambers it can't add pressure to the pedal side which is what generates assist. Unless it's absence allows something to overextend and open the control valve?

    If the pedal feel gets better with cold weather then it probably still needs to be bled better.
     
  13. rob260

    rob260 Administrator Staff Member

    I'm invisible lol... Bleed it again
     
  14. Fists

    Fists Well-Known Member

    You never said that, are you abusing your admin powers to look like you were right? :p

    I like to entertain the idea that it is bled, because sometimes, occasionally, it is lupus.
     
  15. MaxxAction

    MaxxAction New Member

    I did that Friday. I unbolted the slave, and pushed he plunger to try to displace any air upwards. Then I blocked the arm from moving and had the wife push the pedal til it stopped, and bled both points again like that, and got one little bubble out of the upper bleed point.
     
  16. For what it's worth I had a similar problem in my '92 2+0 TT
    Drove it to them mechanics when it finally went totally weird for 1.5kms with no clutch. That was interesting to say the least with a set of lights and 4 roundabouts!
    Was diagnosed as master cylinder - the slave had been replaced months earlier.
    Replaced the master and a week later back in the same hole. Went back inn thankfully with a misbehaving but usable clutch and it was discovered the problem was actually a leaking braided hydraulic hose. They were good and compensated for the cylinder that didn't need replacing.
    It might be worth carefully checking the lines.
    Best regards
    MGR

    Ron
     

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