Sutck disc brake piston and no bike shop to fix it

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Sutck disc brake piston and no bike shop to fix it

Postby willsmother » Sun Apr 07, 2013 11:05 pm

Hoping for advice of a very basic nature, as I am stuck in East Timor and I think one of my rear caliper pistons is sticking (Shimano M485 on Giant Alias MTB) . When I press the lever it "catches " before continuing in and working the brake. When I look at the rotor, one side (the inside side closest to the wheel) doesnt seem to want to move like the outside one does. So the rotor moves a little bit each time. We have big hills so I would like my brakes to work. At this stage most advice would sensibly be take it to LBS, and that I would love to do but we don't have one in the country. I know how to change brake pads but not yet how to bleed brakes. Also I really do think the piston is sticking and that would make sense because we are just finishing the rainy season and there will surely be a great deal of crud in there even though I wash the bike regularly. I can't get neat isopropyl alcohol to clean pistons with but I do have alcohol wipes (the small ones for medical use). I do have brake mineral oil. I don't have a bike stand. Can get syringes and tubing, and have a good multi tool with a disc brake separator and a small shifting spanner and a Leatherman tool. I am a single woman and not very mechanical but have had to learn while here. I can order parts online but do't know if I need any. Could anyone please help me with advice as to how to fix this problem, bearing in mind that I would really appreciate technical information being simplified as I am pretty intimidated by the job ahead of me
Apologies for posting this in two places, I put it on the MTB forum first then realised this board was for technical issues
Thankyou
Helen
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by BNA » Sun Apr 07, 2013 11:08 pm

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Re: Stuck disc brake piston and no bike shop to fix it

Postby Nobody » Sun Apr 07, 2013 11:08 pm

Hopefully someone will be along to give you good advice. I don't have hydros but I have rebuild car hydro brake calipers and they were not very simple. Maybe watching some youtube videos on caliper overhaul and bleeding may help.

Another option to repair would be to order an Avid BB7 or similar cable disc brake, some V brake levers and MTB brake cable. That way you could convert the rear to cable disc and not have to worry about the hydro fix until you get back to AU. If you are there long term, then covert both brakes to cable disc to make servicing and repairs easier.
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Re: Stuck disc brake piston and no bike shop to fix it

Postby trailgumby » Sun Apr 07, 2013 11:33 pm

I had a sticky piston problem on my XTs awhile back. Prevention is the best cure - directing the hose (gentle spray) down through the brakes after a ride to wash accumulated dust off before it can harden in place has stopped it recurring.

Fixing it requires patience, a pack of cotton bud ear cleaners, and brake cleaner spray.

Basically it was a case of easing out the brake piston as far as you can without popping it out, one side at a time, and using the cotton bud and brake cleaner spray to clean the grunge off the piston wall all the way around. First one piston, ease back in, do the other. The idea is to unstick each side enough so they retract evenly. I use tyre levers to hold one side in place while easing the other out, and to push back into place to test the action.

If one side retracts better than the other, eventually one brake pad will move out and drag on your rotor and you get that really irritating "ee-ee" noise each wheel revolution. And of course your brake pad wears out prematurely.

Needless to say, take care not to get any brake fluid on our pads if you do make a slip and pop out a piston a little far. In which case a brake bleed is also required before using our brakes again.

I'd also suggest brake fluid replacement, as a lot of crud does get past teh piston seal and can affect teh action too.

Hope this helps.
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Re: Sutck disc brake piston and no bike shop to fix it

Postby jackthelad » Mon Apr 08, 2013 1:15 am

http://techdocs.shimano.com/techdocs/bl ... ID=jSAKTIc
heres the link u need
print out manual u need
good luck
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Re: Sutck disc brake piston and no bike shop to fix it

Postby RonK » Mon Apr 08, 2013 6:56 am

willsmother wrote: When I look at the rotor, one side (the inside side closest to the wheel) doesnt seem to want to move like the outside one does. So the rotor moves a little bit each time.

Helen, what you are describing sounds like fairly normal operation for a single-piston floating caliper brake.
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Re: Sutck disc brake piston and no bike shop to fix it

Postby MattyK » Mon Apr 08, 2013 9:41 am

RonK wrote:Helen, what you are describing sounds like fairly normal operation for a single-piston floating caliper brake.

Which would be great if the M485 wasn't a twin piston caliper...
http://techdocs.shimano.com/media/techd ... 648520.pdf
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Re: Sutck disc brake piston and no bike shop to fix it

Postby jules21 » Mon Apr 08, 2013 12:57 pm

Helen - there can be a few potential causes of piston binding. i'd recommend your first port-of-call is to clean the piston surface. to do this, remove the brake pad which is on the same side as the stuck piston (the one that lags behind the other in actuation). then apply the brakes - as the 'good' piston engages the disc rotor, the 'bad' one will be forced outwards. don't push it out too far - just enough that you can get access to it to clean. they don't move much - it's just a few mm. if you go too far, it will pop out, or break the seal and you'll need to bleed the system.

once you've got the piston in the position you want it, remove the rear wheel to get better access to the piston and clean it with whatever you can get. give the whole area around it a good clean. do not get anything on the pads - or they may become contaminated and useless (some substances are worse than others - to be safe, ensure you have removed the pads before cleaning the piston(s)).

if there is gunk in there, it may have been the cause of the piston binding and your problems may be solved by cleaning. I can't guarantee that - a worn piston seal could be another cause and you won't solve that by cleaning - you'd need to rebuild the caliper, which is not an option from what you're saying.

good luck.
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Re: Sutck disc brake piston and no bike shop to fix it

Postby willsmother » Mon Apr 08, 2013 10:08 pm

Thankyou to everyone who has replied so far. I am going to take a break from Dili for a few weeks (cycling on rented bikes in Europe, where maintenance is someone else's problem) . When I come back hopefully I will be refreshed and renewed and will have the energy to tackle this (to me) daunting problem. I like the idea of putting cable brakes on but not the thought of actually doing it....
How hard is it to put them on?? Would they fit on my existing rotors?
On my existing mounts?
Many thanks to all
Helen
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Re: Sutck disc brake piston and no bike shop to fix it

Postby Nobody » Mon Apr 08, 2013 10:17 pm

willsmother wrote:I like the idea of putting cable brakes on but not the thought of actually doing it....
How hard is it to put them on?? Would they fit on my existing rotors?
On my existing mounts?
Many thanks to all
Helen
If you can put standard rim brakes on, then you can do cable discs too.
BB7s come with a number of standard brackets from memory. They should fit your standard mounts and if you buy a brake for the same size rotor, then the rotor should fit too. Often you get the brake with a rotor anyway, so better to use the one it comes with.
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Re: Sutck disc brake piston and no bike shop to fix it

Postby willsmother » Mon May 06, 2013 1:36 am

Back from Europe (great road biking trip). jules21 you were right. My friend came round and did just what you described. Cleaning the gunk out and freeing up the stuck piston worked. We did the front one while we were at it. Put new brake pads on so brakes good as new. Will clean pistons most carefully at each pad change now. Lesson learnt.
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Re: Sutck disc brake piston and no bike shop to fix it

Postby nico3d » Tue May 07, 2013 12:58 am

This thread is a bit old and I just joined. I'm riding in Indonesia and I'm having a nightmare finding 36 holes rims. I am on the way to TImor Leste to get a new visa and I'm wondering if you guys dscussing here know a place in Dili where to find new rims. At this stage, I don't even care if they are cheap chinese ones as long as they can get me to a good bike store. The ones I'm using now are completely cracked and I have no clue how long more they are gonna go for.
Any help will do!

thanks!
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Re: Sutck disc brake piston and no bike shop to fix it

Postby nico3d » Tue May 07, 2013 1:06 am

Hi Helen,

I just joined in search for some help and for what i've read it seems you know Dili or even live there. I'm on the way there to get a second indonesian visa and I'm completely frustrated because both of my rims are completely cracked and in Indonesia it seems to be impossible to find rims that have 36 holes, everybody uses 32 here because everybody is on disc brakes, I'm not.
So, do you have any idea where in Dili I should be able to get a pair of rims? At least what stores I could visit? Even if they are cheap chinese ones that will get me somewhere should suffice for now.

Thanks for any help you can provide!
nico
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Re: Sutck disc brake piston and no bike shop to fix it

Postby willsmother » Tue May 07, 2013 10:06 pm

Hi Nico3D. There's a small bike shop here and they are really good at building wheels (not good at fixing hydraulic brakes though) I do live in Dili. They may well be able to help you. They are in any case the only shop. For taxi purposes, they are on the Comoro Road opposite the Presidential Palace, actually, one of the palaces, just up from Tiger Fuel. Not everyone here has disc brakes and you may be in luck, but on the other hand, most of their stock does come from Indonesia. WOrth a try anyway. When do you arrive??? If you want, I can go there tomorrow afternoon and have a quick look and let you know. It is close to where I live. You would need to spell out exactly what you want. Does it matter about the number of holes if they can build an entire wheel??
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Re: Sutck disc brake piston and no bike shop to fix it

Postby willsmother » Tue May 07, 2013 10:07 pm

And if you want a ride while you are here, there are a few of us ride regularly. Lots of hills.
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