1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Caliper piston seal

Discussion in 'Brakes' started by georgecook, Sep 11, 2017.

  1. georgecook

    georgecook Member

    Am in the process of overhauling my rear callipers and would appreciate clarification regarding the correct fitting of the piston seals. My workshop manual states on page 39L of the Braking system section under the heading Rear Calliper Assemble paragraph 4 "Fit the new seal to the hydraulic piston, so that the smaller diameter of the seal is nearer the pointed end of the piston"
    By doing so, this would mean that the lip of the seal is at the opposite end to the fluid pressure and that both my original seals are fitted incorrectly. I must be missing something here.
  2. quattro

    quattro Well-Known Member

    Stand the piston up so the pointed bit is at the top, and fit the seal so its looks like a skirt, hem downwards.

    I hope that makes sense :)

    rear caliper overhaul

  3. harveyp6

    harveyp6 Well-Known Member

    That sounds right to me. The fluid comes into contact with the end of the piston that doesn't have the point, so the wider edge of the seal needs to be closest to the fluid.
  4. georgecook

    georgecook Member

    Sounds right to me too, and that is the way I will fit the seals. Would for some reason be happier if someone could back me up regarding the mistake in the manual. Could anyone check their manual please?
  5. thamesroverp6

    thamesroverp6 Member

    wouldn't surprise me if it was wrong.
    I'm no mechanic but realised one of my manuals had a diagram of the ht leads , one lead incorrect sequence, ha
  6. quattro

    quattro Well-Known Member

    I don't know if this is just me, but the manual is correct. The smaller diameter goes towards the top, i.e. the bit with the point on it, leaving the larger diameter downwards towards the pressure side.

  7. georgecook

    georgecook Member

    Maybe my replacement seals are non standard, but they are similar to the one's fitted and they have the smaller diameter towards the bottom.
    There may be some misunderstanding here( I wish I was capable of adding a photograph to this thread) the seals comprise of a normal seal shape but with an additional smaller diameter added to the end which I believe is the sealing lip.
  8. quattro

    quattro Well-Known Member

    The only picture I have is of an old one which doesn't show it too well. The seal will look like the little drawing above the piston, i.e. with the skirt facing downwards. There is like a double layer on the bottom of it which opens out when fluid pressure is applied to it forming a tighter seal.

    Piston skirt.JPG

    The Braking SYstem / Rear Caliper.jpg
  9. Vern Klukas

    Vern Klukas Member

    A rough sketch.


    Attached Files:

  10. georgecook

    georgecook Member

    Thanks fella's. Can't get clearer than that. Perhaps the manual is not wrong, but misleading.

Share This Page