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  1. #1
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    New question here. Hope Mini piston issues

    Hi. I picked up one of the original Hope Minis as part of my build. It appears to be in very good condition, but one of the pistons seemed stuck so thought id strip it down and see whats what. Iv stripped down Grimeca and Brembo calipers on motorbikes before so im not a total noob with brakes, just with the MTB setups

    The issue is around the pistons and bores. Looking at my caliper halves i initially thought i had small pistons running in machined bores that were pressed into the caliper body. strange.

    However, looking at pic number 11 on the rebuild thread (link below) they seem to have the pistons running straight in the caliper body, and dont have what apppear to be some kind of collars sat inside the pistons like i do? confused! anyone shed any light?

    http://steveukmtb.wordpress.com/hope...iper-overhaul/

    Ive attached 2 pics of my caliper, as split. Hopefully you can understand what i mean?

    Thanks! Paul
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    UK MTBer

  2. #2
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    So there's a sleeve inside of the piston? That doesn't sound right. Especially if you look here at the Hope CAD drawing of the Mini caliper:

  3. #3
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    Have you popped the pistons out yet? You can do that with a floor pump and your finger over the fluid hole. Make sure to put a rag over the piston so it doesn't go shooting across the room. Take a picture of the caliper and piston. I have an extra caliper and pistons out in the shop left over from when I ran the original Minis.

  4. #4
    ballbuster
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    I'm doing mine....

    Quote Originally Posted by santacruzflyer
    Have you popped the pistons out yet? You can do that with a floor pump and your finger over the fluid hole. Make sure to put a rag over the piston so it doesn't go shooting across the room. Take a picture of the caliper and piston. I have an extra caliper and pistons out in the shop left over from when I ran the original Minis.
    The floor pump trick worked great. I had to hook up the brake line to the caliper at one end with the banjo fitting. It just so happens that you can screw the lever fitting into a presta pump connector if there is enough of a rubber gasket in the pump head. The piston popped right out.

    More important that the piston shooting out, the fluid is going to spray a bit when it pops. Wear eye protection. You reeeaaally don't want DOT brake fluid in your eyes.

  5. #5
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    Sorry of no help to your issues. Just chiming in to let you know what an awesome choice you have made with the original minis. I have been running them since 02' without any problems. When I ever need another brake setup Hope would be my choice.
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    http://www.youtube.com/watch?v=qqpcBpSsj1A

  6. #6
    ballbuster
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    Just replaced the pistons in my caliper. Easy peasy. The hardest thing was re-inserting the pistons, and getting them started past the seals. Lubing them up with DOT 5.1fluid on a q-tip helped. I found it was easiest from the inside of the rotor slot to the outside, not through the bore cap like the diagram shows.

    BTW, I hope I put the new pistons in the right way. The diagram shows the older alu/stainless steel pistons. I couldn't find a reference online for how they went, so I guessed. The phenol pistons have one side that has 'A1' stamped into it, and a nicely finished dish on the other end. I put that dished end towards the pads, and the 'A1' side to the fluid side.

    Turns out my circlip pliers wouldn't fit in the lever body to get the clip out, so I had to buy another one from Harbor Freight. Gonna take a stab at the lever tonight.

    Dang, I wish I got pics of the caliper apart. When I do the other one, I'll be sure to snap a couple.



    Last edited by pimpbot; 05-14-2011 at 06:25 PM.

  7. #7
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    "The phenol pistons have one side that has 'A1' stamped into it, and a nicely finished dish on the other end. I put that dished end towards the pads, and the 'A1' side to the fluid side."
    Pimpbot, i'm almost certain that you have these pistons the wrong way around. I have rebuilt a TON of Hope calipers and levers.
    Cheers, Bob.

  8. #8
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    Replacement piston for Hope Disc Brake Calipers.The new hope piston is a phenolic resin which drops a few grams off the brake. This phenolic material also aids the heat dissipation of the brake.

    Correct orientation for fitting:

    There are two letters embossed on the piston - these should face towards the pads - ie out of the caliper. This is the same as the square edged recess facing out, the angled recess facing in.


    This from CRC web site.

  9. #9
    ballbuster
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    Oh, okay...

    Quote Originally Posted by MrBadger
    Replacement piston for Hope Disc Brake Calipers.The new hope piston is a phenolic resin which drops a few grams off the brake. This phenolic material also aids the heat dissipation of the brake.

    Correct orientation for fitting:

    There are two letters embossed on the piston - these should face towards the pads - ie out of the caliper. This is the same as the square edged recess facing out, the angled recess facing in.


    This from CRC web site.
    Thanks for finding that. I also found another reference that says the same thing.

  10. #10
    ballbuster
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    Oh, crap!!

    Quote Originally Posted by pimpbot
    Thanks for finding that. I also found another reference that says the same thing.
    Note to anybody out there... don't put the pistons in backwards or they get seriously stuck. I think I might have to actually fill them with brake fluid and eject the piston with lever pressure. I can't get enough pressure from a tire pump.

    I also found out that I put the lever seals in backwards. That is the downside of taking it apart one day, and putting it back together the next. I put it together the first time without a diagram, then looked at the diagram later that night. WUPS! Good think I don't work on anybody else's bike for money.

  11. #11
    ballbuster
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    Okay...

    Quote Originally Posted by pimpbot
    Note to anybody out there... don't put the pistons in backwards or they get seriously stuck. I think I might have to actually fill them with brake fluid and eject the piston with lever pressure. I can't get enough pressure from a tire pump.

    I also found out that I put the lever seals in backwards. That is the downside of taking it apart one day, and putting it back together the next. I put it together the first time without a diagram, then looked at the diagram later that night. WUPS! Good think I don't work on anybody else's bike for money.
    I managed to pop them out with the tire pump. I had to shove loads of grease in there, and try to work it into the seal. I took it all apart, did a Silkwood Scrub of everything to degrease it, lubed it up with brake fluid and got it back together the right way. I also fixed the seals on my lever.

    Now, new brake hoses and reinstall.

    I still have to rebuild my front. I'll try to remember to take more pics of that brake when I get it apart.

  12. #12
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    I'm not sure if it works the same on the mini, but when I stripped my Enduro levers I found it really hard to get the circlip out and back in again. Something that helped enormously was putting the brass bushing that screws onto the pushrod (the bit you screw in or out to adjust reach) onto the pushrod and then zip tying it down so that the pushrod and piston was pushed into the lever. Then it was a cinch getting the circlip back in.

    btw, if you think getting pistons out is hard, try doing a 4 piston caliper

  13. #13
    ballbuster
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    Yikes!

    Quote Originally Posted by mattthemuppet
    I'm not sure if it works the same on the mini, but when I stripped my Enduro levers I found it really hard to get the circlip out and back in again. Something that helped enormously was putting the brass bushing that screws onto the pushrod (the bit you screw in or out to adjust reach) onto the pushrod and then zip tying it down so that the pushrod and piston was pushed into the lever. Then it was a cinch getting the circlip back in.

    btw, if you think getting pistons out is hard, try doing a 4 piston caliper
    Yeah, I had a bit of a trick getting that lever circlip back in there. My pliers were too fat to fit, and the only other pliers I could find had multiple heads that bolt on to the handles. Those switchable head pliers were so flexy that the snap ring would spin around when I applied any squeeze to them. I got it, but it took a while.

    I also have a dental pick kinda tool set. I used the 90 degree pick in the piston pushrod allen hole, and pushed on that . That worked well.

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