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Master brake cylinder rebuild - 82 xj750 Maxim

Discussion in 'XJ Technical Chat' started by jonathancvb, Jul 30, 2021.

  1. jonathancvb

    jonathancvb New Member

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    Hey all.

    So I purchased a master cylinder rebuild kit from Len at xj4ever (amazing service by the way) and am currently in the process of disassembling the existing parts. I must say, I am quite pleased with myself. I was able to remove the snap-ring without purchasing the fancy 90 degree circlip pliers. Instead, I managed to grind and hand-file my own out of an old pair of needle-nose :D:D:D (see first photo)

    But now I am stuck. I cannot understand what the remaining black plastic part (2nd photo) or how to remove them. I figure they have something to do with the 'low fluid' sensor since I removed the float and they are connected by wires (3rd photo) that runs to the screen.

    Can anybody give me some direction here?

    Two other questions:
    1. how do I remove the rubber seal inside the plunger?
    2. clearly the reservoir is quite dirty. What would be the best stuff to soak in if I was to leave it overnight?

    Thanks in advance
     

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  2. Franz

    Franz Well-Known Member

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  3. jonathancvb

    jonathancvb New Member

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    Thank you for this Franz! Definitely helps.

    EDIT: Ignore my second question, I was able to answer it for myself.
     
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  4. Franz

    Franz Well-Known Member

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    I hope you can see the images of the rebuild l cannot.
     
  5. jonathancvb

    jonathancvb New Member

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    No, I wasn't able to either, however I have been able to figure out the correct configuration for the new parts.

    I am still looking to understand how to remove the sensor post or if I even need to at all. Also, Im looking for information the the pressure relief hole.
     
  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    When you get the master cylinder stripped out. You use a small wire clean up the pressure relief hole
     
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  7. jonathancvb

    jonathancvb New Member

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    Yes, I was aware of this.. So yesterday, after successfully disassembling the majority of the cylinder parts, I attempted to use the wire provided in the kit to clean the port. I could not get the wire through the port. I ended up taking a small drill bit (probably not nearly small enough) and tried to clean it by spinning it in the hole lightly by hand. I soon discovered that even though there was an area that had a tiny countersink in the aluminum body, there was in fact NO hole. My curiosity and impatience got the best of me and I continued to spin the bit until eventually I was able to make a hole into the cylinder bore. My dilemma now is that there is a small burr inside the bore and I'm concerned that the hole is too big than intended. I am also confused as to why there was no hole to begin with, unless I was looking at the wrong spot, but I am quite confident that's not the case. I have been looking online for an answer for hours and cannot seem to figure this out.
     
  8. Timbox

    Timbox Well-Known Member

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    Do you have a good pic of what you have done to the master now that you have that hole? That would help us out....thanks
     
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  9. jonathancvb

    jonathancvb New Member

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    See photos below. On the first one you can see the hole I drilled at the bottom of the reservoir. The second photo is difficult to see but there are two small reflections of light about halfway down the bore, the further and smaller one is the hole I made, which now has a burr that I will have to somehow file down



    y16.jpg y17.jpg
     
  10. XJ550H

    XJ550H Well-Known Member Premium Member

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    take a small dowel as close to the whole size as possible for the piston and tape a piece of wet dry sandpaper to it you should be able to remove the burr that way don't lean on it too hard
     
    Last edited: Aug 1, 2021
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  11. Mechanic1978

    Mechanic1978 Active Member

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    I would not take any abrasive to the inside of the piston bore. its aluminum, and the slightest scoring in there will likely render it useless. If them new seals dont get a perfectly clean and smooth bore to move in, it will likely not build and pressure, or pressure will fade. abrasives in there are not a good idea..

    Drilling the hole larger is also not a good idea, as those two holes are a speciffic size for a reason, they both function as the piston slides past them, now one will function faster, and may have a loss in pressure. the two holes are positioned in specific locations of the piston chambers for timing of the fluid flow, and now it has been altered.

    I have my fingers crossed for you that it still functions correctly....
     
  12. XJ550H

    XJ550H Well-Known Member Premium Member

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    if he is carful he should be able to remove burr.
    nothing to lose as he may need a new mc anyways.
     
  13. jonathancvb

    jonathancvb New Member

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    Thank you both for you input. I have spent hours and hours reading up on this and I realize the risk I took and the fact that I may need to replace the whole MC now. Anyway, I purchased an old and used bike to learn on, and learn I have. Today, hopefully I will have the whole thing properly cleaned up, then I can put it all back together!
    Exciting stuff!
     
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  14. Timbox

    Timbox Well-Known Member

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    It that a burr? Or is that just left over old dried brake fluid? I would get in there with a lot of parts cleaner or some B12 chemtool and get that area so clean it shines. Then I would see if that burr comes off or is it in the bore. To scratch that bore would have taken the spring to be compromised and scratch it when used over and over. Q tips, compressed air and rags, clean that up really good and see what you have.

    As far as the top little hole, I think it looks good and you did a good job on that. You still might be able to save the MC.
     
  15. jonathancvb

    jonathancvb New Member

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    Thanks for the tips,

    So.. I acutally had the MC sitting in parts cleaner for the last 24 hours. See pictures for the results....

    Can someone explain to me what I did wrong. Now I still have to clean the stupid thing and am at a bit of a loss with how to do it well.
     

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  16. Huntchuks

    Huntchuks Well-Known Member

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    You can use paint stripper and then repaint it. Sorry, but the first picture made me chuckle.
     
  17. XJ550H

    XJ550H Well-Known Member Premium Member

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    did not read directions?
    DIRECTIONS Note: Some surfaces such as aluminum alloys, plastic or painted surfaces are inherently sensitive to alkaline cleaners. Do not use on motorcycles or glass. Spot test on ALL surfaces before use. Do not inhale mist. Use with adequate ventilation. The use of safety glasses and protective gloves is recommended. These directions must be followed or damage may result. 1. Before degreasing, be sure that all surfaces are cool to the touc

    PX-0352C Front.ai (petroleumservicecompany.com)
     
  18. jonathancvb

    jonathancvb New Member

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    Haha! Good, it's pretty funny.

    Doesn't say that anywhere on the bottle I bought... o_O

    Im not concerned about the paint at this point. I just want to clean it properly so I can put it back together..
     

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