hope mono 3 - stuck piston

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8mph

Veteran
Location
Devon
Hi, the piston is stuck in the calliper, pressing the lever does nothing. I would probably try blowing it out with a compressor if I had access to one. Anyone got any neat tricks?
I'm stumped.
The only thing I can think of is utterly daft and involves super glue and a stick. Please help me!
 
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fossyant

Ride It Like You Stole It!
Location
South Manchester
Can you strip the calliper - I.e. dis-assemble it. Don't try compressors etc....

This guy help ? I see the calliper is one piece !!!


View: https://www.youtube.com/watch?v=bDfpphvWjN4
 
OP
OP
8mph

8mph

Veteran
Location
Devon
Hey, thanks. I watched that video yesterday but it doesn't help much as there is no access from the outside of the calliper, nothing to screw off just two halves of solid aluminium.
I might be able to source new pistons, so wrecking the ones that I have could be an option. I'm thinking of buying a new ( second hand) calliper and selling
this one for parts just to be able to ride!
Thanks for taking the time to reply!
 
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Location
Loch side.
Take it to a garage and have someone blow it out with compressed air. Wrap it in a cloth first, because the piston comes out with force and a spray of brake fluid.

No need to concoct a connector, just hold the air blow nozzle against the bleed nipple. It will come out. If the other piston is already out, put it back and hold it in whilst this one is blasted out. There really is no other way.
 
OP
OP
8mph

8mph

Veteran
Location
Devon
Take it to a garage and have someone blow it out with compressed air. Wrap it in a cloth first, because the piston comes out with force and a spray of brake fluid.

No need to concoct a connector, just hold the air blow nozzle against the bleed nipple. It will come out. If the other piston is already out, put it back and hold it in whilst this one is blasted out. There really is no other way.


Thanks so much, I'll do that before I end up mangling them!
 
OP
OP
8mph

8mph

Veteran
Location
Devon
Considering the price of Hope callipers that's a bit crap really.
I bought a second hand bike with a disk break and rode it for ten months without bothering to find out how the thing works. My bad I think!
Hopefully, I'll have the thing apart soon.
 
OP
OP
8mph

8mph

Veteran
Location
Devon
Take it to a garage and have someone blow it out with compressed air. Wrap it in a cloth first, because the piston comes out with force and a spray of brake fluid.

No need to concoct a connector, just hold the air blow nozzle against the bleed nipple. It will come out. If the other piston is already out, put it back and hold it in whilst this one is blasted out. There really is no other way.

Done! Thank you for the tip. So glad that I didn't spend money on a new caliper. The garage were happy to help.

IMG_20190624_130543.jpg
 
For potential future readers, a grease gun can be used to push caliper pistons out.
 
OP
OP
8mph

8mph

Veteran
Location
Devon
I looks as if the seals need replacing and I've also managed to lose the o ring somehow so it's an ongoing job, but I'm hoping to get it restored to fully functioning with new pads, seals and a bleed . In the meantime, I have fitted a £14 Clarks mechanical brake which took quite some time to adjust but at least there was no mess.
Off for a ride now. Thank you all for your replies!
 

Globalti

Legendary Member
A Joe Blow track pump comes with a yellow plastic conical nozzle for inflating lilos and that can be screwed tight into the threaded hole, in which the bleed nipple fits. It cuts its own thread and stays in securely. Block the outlet with a finger, cover the piston with a cloth then push the pump hard for a long time. The piston will slowly ease out and come free with a loud pop.

Most people don't realise how tightly brake pistons fit into their seals; they think the piston slides in and out but in fact braking happens when hydraulic pressure deforms the seals and the piston only creeps through microscopically as the pads wear.
 
OP
OP
8mph

8mph

Veteran
Location
Devon
Most people don't realise how tightly brake pistons fit into their seals; they think the piston slides in and out but in fact braking happens when hydraulic pressure deforms the seals and the piston only creeps through microscopically as the pads wear.

Thanks for pointing that out, I was slightly perturbed that the piston felt so stiff inside the seal.
There is some corrosion on one of my pistons, the mechanic who helped me out said to give it a light rub with some wet and dry.
Bearing in mind what you have said, I'll not go overboard with the polishing.
 

Globalti

Legendary Member
I really wouldn't score or abrade the piston, the fluid pressures are high and even slight leakage will contaminate your pads and make the brake squawk and judder. If you must clean the pistons do it with a polish like Solvol Autosol or car polish.
 

JhnBssll

Veteran
Location
Suffolk
You can buy Acetal (tough plastic) pistons from Hope to replace the aluminium ones. I use these every time I rebuild an old caliper as they dont corrode. The newer hope calipers have acetal pistons from new
 
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