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Thread: K24 problems

  1. #1
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    K24 problems

    Anyone have any service info for Oro calipers? I'd call Formula, but they're closed for the weekend and I'm hoping to ride.
    One of the pistons in my rear caliper is leaking fluid onto everything. I've got a couple of o ring and piston seal kits coming, but I'm not sure about the best disassembly and assembly procedures. I've got the tools and skills to do the job, but I'd rather make sure I'm doing it right than to guess and be wrong.
    Last edited by ric426; 05-15-2009 at 08:49 PM.

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    I'll be more specific. Once I'm ready to put the new piston seal back in, what surfaces, if any, should be lubed before reassembly and with what? I know the square seal is supposed to retract the piston when the pressure is released, which would lead me to think that there shouldn't be any lube between the piston and the seal, but I could be wrong. What about between the seal and the cylinder bore?

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    Getting the old pistons out is tricky. Some advocate using compressed air to force them out, which is probably quicker but I did the following.

    If the pistons are well and truly stuck you can rotate them with a 10mm allen key, although there is a risk you'll damage the piston. Hopefully you won't have to do this!

    I found it easiest to change the pistons one at a time. Hold one piston in place with a spanner/screwdriver etc and pump the lever to force the other piston out.

    Then take the caliper apart, replace the piston and seal, smear with the grease you get with the kit. Not too much but a smear over the seal and piston

    Then put the caliper back together, do a rough bleed, and force the other piston out the same way and replace.

    No need to grease anywhere else

    Once you've rebuilt, take the time to do a thorough bleed and wipe off any excess grease.

    DOT fluid isn't very nice stuff so I'm presuming you know to wear gloves.

    Took me 45mins to do the whole thing.

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    Thanks, you've confirmed what I suspected once I got the pistons out. I used compressed air to pop the pistons out, but it wasn't working at first because, until I got a rubber tip for it, I wasn't getting a good enough seal on the blow gun nozzle to get enough pressure. One thing I haven't seen mentioned in this forum is that you need to be careful about the mist of DOT4 fluid that forms from the high pressure air. I don't think you want to inhale any of that. I wrapped the caliper in a shop towel when I did mine and there was a good spray of fluid on it.
    My kit didn't come with any grease, but I bought a tube of silicone grease for the seals in a paint ball gun, which I suspect will be compatible. I coated the O.D. of the pistons and the inner surface of the seals with a thin film and the pistons went in smoothly with a little thumb pressure.
    I put it all back together but had to reuse the o ring that goes between the two caliper halves because the one supplied with the kit wasn't nearly thick enough to contact both halves, let alone form a seal. I spent the time to do a really thorough bleed with the system on the bench and left it in a vertical position overnight with the lever pulled and this morning it's nice and solid with no leaks (so far). Mounted back on the bike, the rear brake feels more solid than it ever has. I'll go on a ride later today and see how it holds up. As long as it doesn't leak I'll be a happy camper.

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    I bought the piston and seal kit, which does come with grease. Formula are bit tight if they don't send any grease with the seal kit!

    Good call with the inhalation though - I'd never have thought of that. I had a sore chest the last time I seated tubeless tyres because of inhaling all the washing up liquid vapour :-/

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    Quote Originally Posted by RicB
    Good call with the inhalation though - I'd never have thought of that. I had a sore chest the last time I seated tubeless tyres because of inhaling all the washing up liquid vapour :-/
    When I first tried popping the pistons with my other blow gun attachment there wasn't enough pressure to push the piston out, but there was enough to blow air past the seal and there was a puff of misted brake fluid because I hadn't covered the caliper with anything. I caught of a whiff of it and instantly knew it wasn't good. I had a nasty taste in my mouth for about an hour even after rinsing my mouth and gargling with water a few times. Hopefully there aren't any long term effects, but if I come down with some mysterious malady in 10 or 20 years I'll have something to blame it on.

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    Quote Originally Posted by ric426
    Mounted back on the bike, the rear brake feels more solid than it ever has. I'll go on a ride later today and see how it holds up. As long as it doesn't leak I'll be a happy camper.
    Well, I thought I had things fixed for good, but twice on a ride today the lever pulled all the way to the grip with no braking action on the first pull. Not a good feeling on a fast downhill. On the second pull, everything behaved as normal and felt solid. I doubt it was a heat issue because there just aren't any places on the trail requiring more than a few seconds of braking and both times I'd been on flat areas prior to the weirdness. Does this sound like a bleed issue? I thought I was pretty thorough last time and the system has felt more solid than it ever has, but there's still some sort of problem happening.

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