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Thread: Rebuilding 84' 250r rear caliper and master cylinder

  1. #1
    Join Date
    May 2017
    Location
    Australia
    --
    98

    Rebuilding 84' 250r rear caliper and master cylinder

    So I'm rebuilding my rear caliper and brake master cylinder on my 250r.
    What is the best coating to do that will be resistant to brake fluid?
    Here are some pics of the parts



    Also if I were to powder coat one issue is the plastic insert that is stuck in the rear caliper as it will melt in the oven.



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  2. #2
    Join Date
    Mar 2010
    Location
    Slidell, LA
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    4,316
    That e-brake o-ring comes out. Use a 90 degree pic to remove. With the caliper rebuild kit you will get another one as a replacement. I would use black powder on both of those items.
    Feedback for yaegerb: Click Here

    Need something blasted or polished or both? Send me a PM

  3. #3
    Join Date
    May 2017
    Location
    Australia
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    98
    Quote Originally Posted by yaegerb View Post
    That e-brake o-ring comes out. Use a 90 degree pic to remove. With the caliper rebuild kit you will get another one as a replacement. I would use black powder on both of those items.
    Thanks mate, but I bought genuine seals and the plastic cup I couldn't find on partzilla when ordering. Hopefully I can remove it without damaging it. I'm going to run a park brake block off plate anyway also if that has any implications.
    Cheers


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  4. #4
    Join Date
    May 2009
    Location
    S.E. Michigan
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    1,117
    I vote satin black powder coat. I did that on my 350x and brother's 250r brakes and during bleeding I've made a crazy mess with brake fluid all over them. The powder holds up just fine.

    With regard to that o-ring: if the 84 is like the 350x and the 85/86 250R, there is a small metal cup retainer that holds the o-ring in the bore. I used a small punch from the outside to tap the o-ring and metal cup out. I'll try to locate the size, but I found an o-ring at the hardware store that was pretty much the exact size (just in case you have trouble getting the OEM one). If I can find the package and size, I'll post up here.

    When putting the metal retainer back in, make sure not to compress the o-ring too far. I did that and ruined one o-ring when attempting to reinsert the piston.

    You need to keep the o-ring in there even if you are getting rid of the parking brake. If not, the entire area between the caliper and parking brake bracket will be open to brake fluid, and worse, your caliper will be open to the air in that space.

    EDIT: I looked up in the parts diagrams and it looks like the same o-ring setup is used. The o-ring is a JIS (Japanese Industrial Standard) P8 size o-ring. Same one is called out for most of the rear calipers on the Honda ATC's. If you pull up whatever your favorite parts site is for OEM Honda parts, it is part number 34 on the diagram, Honda P/N: 91358-964-006.
    Last edited by wonderboy; 06-07-2018 at 09:21 AM.
    - Frank

    1984 200ES Big Red
    1985 350X (x2)
    1986 250SX
    1984 Auto-X
    1984 ATC70
    1985 ATC70

  5. #5
    Join Date
    May 2017
    Location
    Australia
    --
    98
    Quote Originally Posted by wonderboy View Post
    I vote satin black powder coat. I did that on my 350x and brother's 250r brakes and during bleeding I've made a crazy mess with brake fluid all over them. The powder holds up just fine.

    With regard to that o-ring: if the 84 is like the 350x and the 85/86 250R, there is a small metal cup retainer that holds the o-ring in the bore. I used a small punch from the outside to tap the o-ring and metal cup out. I'll try to locate the size, but I found an o-ring at the hardware store that was pretty much the exact size (just in case you have trouble getting the OEM one). If I can find the package and size, I'll post up here.

    When putting the metal retainer back in, make sure not to compress the o-ring too far. I did that and ruined one o-ring when attempting to reinsert the piston.

    You need to keep the o-ring in there even if you are getting rid of the parking brake. If not, the entire area between the caliper and parking brake bracket will be open to brake fluid, and worse, your caliper will be open to the air in that space.
    Thanks for your insight I appreciate it. Looks like powdercoat is the go if I can remove the black plastic cup. I was able to remove the o ring with a pick. But the metal cup you're talking about is plastic on this caliper and I'm scared I'll break it. If I break it, it will be game over or I'll have to machine one up on the lathe.


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  6. #6
    Join Date
    May 2009
    Location
    S.E. Michigan
    --
    1,117
    I'm really not trying to second guess you, but are you sure it's plastic? On my 350x and (85/86) 250r, it was definitely metal, and the setup looks almost identical in your picture. I guess regardless of material, I think you should be able to gently tap it out if you go from the outside with a relatively flat tool. I agree though, you don't want to break it! It would be a pain to have to make a new one. ABSOLUTE worst case scenario, if you found a junk 350x or (85/86) 250r caliper, you could harvest the metal one from those to use on yours. Given that the o-ring is the same size, the metal retainer from one of these should work.
    - Frank

    1984 200ES Big Red
    1985 350X (x2)
    1986 250SX
    1984 Auto-X
    1984 ATC70
    1985 ATC70

  7. #7
    Join Date
    Mar 2010
    Location
    Slidell, LA
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    4,316
    Quote Originally Posted by oldoo View Post
    Thanks mate, but I bought genuine seals and the plastic cup I couldn't find on partzilla when ordering. Hopefully I can remove it without damaging it. I'm going to run a park brake block off plate anyway also if that has any implications.
    Cheers


    Sent from my iPhone using Tapatalk
    Or just use this rebuild kit....

    https://m.ebay.com/itm/HONDA-ATC250R...kAAOSwttVaS-oR
    Feedback for yaegerb: Click Here

    Need something blasted or polished or both? Send me a PM

  8. #8
    Join Date
    May 2017
    Location
    Australia
    --
    98
    Ok guys so my guru mechanic neighbour popped out the tin cage for me. Happy days. Now to prep both the caliper and master cylinder for powder.



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