Rear master has gone wonky on me

Discussion in 'Mechanics Garage' started by jethro, Aug 12, 2021.

  1. jethro

    jethro New Member

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    I had the rear footpeg mount off and left the master hanging by the hose on my 93. At some point it ended up upside down. Needed to get it inspected once back together and found the rear brake did nothing except move through it's travel. Tried to bleed it and the master just wasn't moving any fluid. I found an oem rebuild kit here in town and installed it along with a Spiegler braided line and the pedal felt amazing. Got it inspected and then on the second ride I started having to push really hard to get any action out of the rear brake and then the 33rd time I rode it it was back to doing little of nothing. I hate to keep putting rebuild kits in and only have them work for a few rides. Any ideas?
     
  2. Darth Vader

    Darth Vader New Member

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    Almost certainly air in the system. Try tightening the banjo bolts again as air can suck in there past the copper washers.Not sure what the torque numbers are but its quite a lot.
     
  3. raYzerman

    raYzerman Member

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    If the pedal is going down easily, master may not be primed, loosen banjo at the MC and let gravity leak a little out then snug it back up. Once primed, it should pump... but I think you got air hiding somewhere...... when you're done bleeding, tie the pedal down for a few hours, air should consolidate or move to the reservoir, then another coupla squirts should get it.
     
  4. jethro

    jethro New Member

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    I went from a perfect high hard pedal to not moving any fluid to bleed. If it wasn't primed I wouldn't have been able to bleed the system in the first place, unless it lost prime which I don't know what would cause that.
     
  5. Simon Edwards

    Simon Edwards New Member

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    Those are 35lbft from memory. As you say that is pretty tight.

    When you fitted the repair kit did you carefully inspect the bore for scoring? A new seal would work for a while then fail on a score mark.

    Likewise the new seal could have caught a bit of grit that was dislodged during the re-assembling and bleeding process. The only way to check would be another strip-down.

    A bit of grit floating around would also have this pedal effect if it happened in the calliper. But if it goes there you would see the weeping of brake fluid around the pad and a drop in the fluid level. If its a seal on the master that is gone you won't see anything much happening anywhere.
     
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