Caliper Piston Removal

Discussion in 'Wheels' started by 90FXRS, Mar 12, 2016.

  1. 90FXRS

    90FXRS Junior Member Contributor

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    I'm needing to rebuild the rear caliper. Slowly leaking and not holding pressure. I got the kit and read through it. They mention a special tool, of course. Can this be bypassed by simply removing the caliper and pads, putting something between the pistons and slowly blowing air into the caliper to get the pistons to move to the point I can remove them by hand? Should I go ahead and separate the caliper and do each side separately? I'm thinking if this is the case then a bag might be in order. Put each half in the bag so pistons don't go flying and bouncing all over the garage. This is on a 2001 Softail, stock calipers.
     
  2. dolt

    dolt Senior Member Contributor

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    Not sure why you are rebuilding the caliper but I would be inclined to disassemble and thoroughly clean every part, polish up the new pistons and coat everything with the appropriate brake fluid when reassembling. Use a thin piece of wood with a shop rag wrapped around it to expose the pistons. The whole point of the direction is to keep the pistons coming out evenly and not turning into shrapnel as they can come out very quickly if you apply too much air pressure too quickly. Recommend you use the minimum amount of air pressure that you can get away with to gently push out the pistons. Once the pistons start coming out of their holes, quite often you can work them out the rest of the way with your fingers and avoid the flying object part of the operation
     
  3. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    Like dolt I use a piece of soft wood with a rag wrapped round it to stop the piston getting too far out with the air once the pistons are most of the way out it is fairly easy to pull all the way out by hand
    You can leave the bleeder slightly open to start with till you know how it is gong but too much pressure and a piston can easily be flying around the bike shed causing all kinds of damage

    Brian
     
  4. 90FXRS

    90FXRS Junior Member Contributor

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    The caliper is being rebuilt because the banjo washers and bleeder have been changed and it still has a leak. It's not a big leak but once it's bled and cleaned it slowly gets a film of fluid and dirt on it and becomes spongy again. The kit comes with a packet of piston lube and specifically says not to use brake fluid as a lubricant. As far as things flying around the garage, I kinda had a vision of Chris Farley with the oil can in the movie Tommy Boy.
     
  5. dolt

    dolt Senior Member Contributor

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    We all have our own way of doing things. I have used a 3M pad to clean using brake fluid as the cleaning agent. Wipe the parts down and reassemble. No issue with using the lubricant at all but if just replacing o-ring and sealing boot, that's how I do it. I think the lubricant tends to attract dirt, etc. but that's JMHO. Hope you get the leak stopped.;)
     
  6. Jack Klarich

    Jack Klarich Expert Member

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    You can use air pressure, but protect the piston, try not to remove too much from the piston it is a machined surface, better to hone the caliper, keep ALL parts clean of debris and use lots of lube on the O ring and piston, that is how I taught my brake class
    Wear safety glasses if you use air to blow out the piston
     
    HDDon likes this.
  7. 90FXRS

    90FXRS Junior Member Contributor

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    Done deal. Test ride tomorrow. I used 2 wooden shims to slowly expand the pistons. Blow a litte air into the caliper, thin the shim.....repeat until they were out. Cleaned everything in denatured alcohol and let dry. used the tube o' lube and it all went pretty easy. Since it is on a Softail and how the rear line routes over the swingarm, I hung the caliper with the pistons collapsed and wedges in place to let any air that went back into the line rise to the occasion. Bled it a few times, installed then came dinner. Test ride tomorrow.
     
    Jack Klarich likes this.