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front brake / tire spin

Discussion in 'XJ Technical Chat' started by riponal, Jul 19, 2016.

  1. riponal

    riponal New Member

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    Just rebuilt the brake caliper, new pads and replaced the brake lines. My question is how much "free spin" should the front tire have once everything is back together? I used a mighty vac to bleed the brake line and it all went well. When I spin the tire it goes maybe a quarter turn before it stops. Took bike for a test ride, brake stops very well, but seems a bit hot (?) Realize the disc will get hot from friction.

    Your input is appreciated
     
    riponal, Jul 19, 2016
    #1
  2. mrdawson

    mrdawson Active Member

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    also rebuild master cylinder?
     
    mrdawson, Jul 19, 2016
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  3. cds1984

    cds1984 Well-Known Member

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    Don't forget that the pistons are basically getting pushed back in by the vibration of the disc spinning when you aren't applying hydraulic pressure via the brake lever.
    So... if you have a slight buckle/warp in the disc you end up with a cold grab if you spin it (like you are doing).

    The single sided calipers also rely on the sliding motion on a lubricated pin to move about so, if that is sticky then it will grab also.
    I wouldn't worry about the heat but if you feel a pulsing type of braking I'd check the slide pins before getting the discs ground to remove a warp/buckle.
     
    cds1984, Jul 19, 2016
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  4. riponal

    riponal New Member

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    no, did not do the master
     
    riponal, Jul 19, 2016
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  5. mrdawson

    mrdawson Active Member

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    as above. but could also be an issue with the MC, I'd rebuild that anyhow since you've already redone the calipers, lines. would make sense to do the MC as well.
     
    mrdawson, Jul 19, 2016
    #5
  6. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Agreed. Rebuild it all or don't even bother.
     
    k-moe, Jul 19, 2016
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    Jetfixer and mrdawson like this.
  7. cds1984

    cds1984 Well-Known Member

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    If you rebuild the Master Cylinder it will 'possibly' remove an issue with fluid being locked in the lines, which would also lock the pistons out and grab on the discs.
    It isn't a big deal to do the rebuild and is definitely recommended.
     
    cds1984, Jul 20, 2016
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  8. riponal

    riponal New Member

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    turns out I didn't have the piston all the way in, I took the caliper off and used a "c" clamp to push the piston in about a 1/32" ( if that much) could tell right away when I put the caliper back on there was more room. Thanks for the suggestions
     
    riponal, Jul 29, 2016
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  9. mrdawson

    mrdawson Active Member

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    as in it was stuck?
     
    mrdawson, Jul 29, 2016
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  10. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Keep an eye on it, and rebuild the master cylinder.
     
    k-moe, Jul 29, 2016
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  11. riponal

    riponal New Member

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    I work the brake lever, the piston came out and sucked back in ever so little, did this a half dozen times. Tried pushing in with both thumbs and wouldn't go in any further, that's when I took the c clamp and it went in just that little bit. Worked the brake lever, it moved in and out. Bolted back onto fork, spun wheel, stopped and released. Rode up and down the street (going pretty slow) and hit the brake, stopped, released. So?? I don't know why it would slide all the way home but a little extra from the clamp got it going
     
    riponal, Jul 29, 2016
    #11
  12. Polock

    Polock Well-Known Member

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    there's nothing to push the piston back except the flex in the seal
    the clamp pushed the piston back in the seal a bit, now the flex travel is farther back away from the disk and the disk spins freer. sooner or later it will be just like it was.
    spin your car tire, that brake will drag too (unless your rotor is warped)
     
    Polock, Jul 29, 2016
    #12

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