Why do my pistons need screwing?

Discussion in 'Car and Van Talk' started by Devil's Advocate, Sep 23, 2017.

  1. Isitreally

    Isitreally Active Member


    I give up.

    Please never do brake on anybody's vehicle.
     
  2. WillyEckerslike

    WillyEckerslike Active Member

    Don't be a kn#b. You said the handbrake adjusts the pistons. If that were the case you would use it to adjust the pistons after a refit. The hydraulics is a closed system so any retraction or expansion of the pistons would cause the fluid to move accordingly. I've said that I'll check at the garage when I get back which I will do but in the meantime your comment about me working on my cars is unwarranted and rude. Oh, I still haven't found a ratchet in a piston. Genuinely happy to be shown otherwise and want to learn more as I've also said so you don't need to be offensive about it.
     
    Devil's Advocate likes this.
  3. Isitreally

    Isitreally Active Member


    Sorry unwarranted remark by myself.

    Have a read of this, American I know but the same principle.

    http://techtalk.mpbrakes.com/how-to-series/rear-brake-caliper-adjustment
     
  4. WillyEckerslike

    WillyEckerslike Active Member

    Accepted, thank you. I'm away now and this is awkward on my phone. I will read it when I can and will pick this up when I get back.
     
  5. Devil's Advocate

    Devil's Advocate Well-Known Member

    That's another point I wondered about, and I'm sure you are right - the piston doesn't rotate even in teeny tiny increments in normal use. It doesn't make sense to me for it to be rotating against the back of the pad in use.
     
  6. Devil's Advocate

    Devil's Advocate Well-Known Member

    Not the case on my Cortina (kit) - it's the footbrake that moves the auto-adjuster. The hand brake just levers the shoes a bit closer when parked.

    I think that, even on modern systems, it's the foot brake that constantly adjusts to compensate for wear - the piston O rings have that amount of springiness in them to do this. But, in the case of 'our' parking callipers, the piston also pulls that insert out with it, and the insert spirals out on the threaded rod each time to maintain the correct spacing.

    The hand brake on the Citroen doesn't need 'adjusting' as such - yes it needs to be set at the right length so that it pulls on the calliper lever without any slack, but that's it. All it does from then on is to pull that calliper lever a quarter-turn (or so) to give that threaded rod that wee part-turn to push the piston out the necessary amount.

    As far as I understand, that threaded rod itself does not ever fully rotate, but 'oscillates' in these quarter-turn parking movements.

    Ergo, I think it's the foot brake that adjusts the brakes, and 'sets' them with newly fitted pads.
     

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