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Brake bleeding issue - I need some help on this one...

Discussion in 'Technical and Troubleshooting Torque' started by Tim., May 26, 2011.

  1. I have a suzuki across I bought to teach my fiancé how to ride. It's a POS but runs well and seems to hold up Ok when she lets it fall over...

    The brakes on it are shot though, and I just can't seem to get them right. I have a fair bit of experience with Mechanics in general, modifying cars and bikes for the past 10 years or so, so something simple like this is really getting to me...

    It seems like there is air in the front system, and I can't get it out. It was like this when I bought it. Initially I thought the hoses were shot (which they were) so braided line. No difference. I flushed and bled the system again still nothing.

    I have tried bleeding from the top, bleeding it with pressure from the bottom, vacuum bleeding from the bottom, still no joy.

    I have disconnected the calliper and master cylinder and tried bleeding them at all different angles to dislodge any bubbles.

    Last night I did some troubleshooting.

    I blocked the master cylinder off at the banjo (just put a cut-down bolt in there) and tried the master. it was like a rock (as it should be!) no give at all.

    I then put the braided line on and blocked the calliper end banjo. I couldn't get a perfect seal, and bleeding it was tricky, but I got it pretty hard, definitely better than it is when connected to the calliper.

    SO I decided the issue was in the calliper, I pulled it down and cleaned the pistons and seals, it all looked fine inside. I tried to note anywhere were bubbles could get caught (so I could maneuver them out later). I put it all back together and bled it again and it was exactly the same as before.

    The lever pulls all the way to the bar. when riding any hard braking has the lever against the bar. If there's an emergency on this bike atm I would recommend avoiding the brakes and jumping off.

    AS I have been struggling with this for weeks, last night I had an epiphany, just put on a bigger MC! with a bigger bore I can just compress the damn air more and get decent braking force from the shitty air-filled system...

    After considering the issues I'm going to have with master/slave piston ratios I decided to have one last go at doing it properly, so, I ask you all, what else can I try??

  2. I've struck this before on some bikes. I've concluded that the pistons on some calipers don't' work properly when they are further down the bore. When the bike is new, the pads and discs are thick and it's not a problem. Eventually, due to disc wear, you get to the point where even new pads won't solve the problem.

    If the pads are good, measure the disc thickness and replace them if they are at the limit.

    A cheaper alternative is to rummage through the pad catalogue and find ones intended for a different model that are a little thicker. You may be lucky.
  3. If it is air, a guy at work told me a good trick.

    Pump the brakes till they get hard, then pull in the lever hand and wrap a bungie cord around it. Leave it overnight.

    Not sure if you can do that given that it comes back to the bar without getting hard...
  4. Do this, then, take the calipers off & push the pistons all the way back in, then go again.

    This should push any air back up through the mastercylinder.

    Good luck.
  5. Do you have a manual? Some bikes have a specific bleeding sequence to work through.

    Don't know the Across set up. Is it twin or single disk? If twin it can sometimes help to start bleeding at the junction where the line splits in two.

    +1 to tying brake on overnight sometimes helping.
  6. I like this idea to cycle through the pistons. I have tried keeping it under compression before, but I think this only helps get the little bubbles out that get caught in there if you are too aggressive during the bleeding process...

    I'll try to give it a go tonight before the thurs night ride.
  7. Worked for me when I changed brake lines, changing calipers soon, not looking forward to it.