Shimano RS785 hydraulic caliper

[Yellow Saddle]

Brakes are a safety item - what the OP was trying to do in the first place shows he didn't really know what he was doing ( no offence to him I might add) so I have to agree with what 'rustybearing' said

And? Do you think the OP is stupid enough to not test them before using them? Also, doesn't he have two brakes on his bike? C'mon, stop this inquisitiveness-is-dangerous nonsense. Next you'll ask him to wear a hi-viz jacket when washing his bike.

 

[Kajjal]

And? Do you think the OP is stupid enough to not test them before using them? Also, doesn't he have two brakes on his bike? C'mon, stop this inquisitiveness-is-dangerous nonsense. Next you'll ask him to wear a hi-viz jacket when washing his bike.

Having as an important component as a brake potentially being unreliable is a risk not worth taking.

 

[Tenacious Sloth]

Having as an important component as a brake potentially being unreliable is a risk not worth taking.

Let's get real about this. He's not going to test the brakes for the first time anywhere dangerous is he?

If mankind had developed with this attitude, we'd still be living in caves. Let him make his mistakes, learn, and then hopefully give future posters some advice based on experience.

Graham

 

[Kajjal]

Let's get real about this. He's not going to test the brakes for the first time anywhere dangerous is he?

If mankind had developed with this attitude, we'd still be living in caves. Let him make his mistakes, learn, and then hopefully give future posters some advice based on experience.

Graham

That's not my point, if the fault reoccurs when at high speed or in heavy traffic it could be a real issue. I have seen someone's brake fail to work and also suddenly jam full on, in both cases they were lucky.

 

[Tenacious Sloth]

That's not my point, if the fault reoccurs when at high speed or in heavy traffic it could be a real issue. I have seen someone's brake fail to work and also suddenly jam full on, in both cases they were lucky.

The OP didn't have a fault during use, apart from suspected excessive lever travel.

His problem is that the piston popped out during maintenance (a facepalm moment that most people who learn by "having a go" can probably sympathise with). I'm assuming that the wheel wasn't fitted at this time as the rotor would prevent the piston coming out past the seal?

It sounds as if the seal has moved and is preventing the piston from going back in fully.

I would have thought a process similar to the following will sort his problem:

1. Relocate the seal correctly (after checking the seal for possible damage)
2. Insert the piston carefully, ensuring it goes fully back.
3. Clean off any brake fluid to prevent contamination of pads/rotor.
4. Fit pads.
5. Refit the wheel so that rotor prevents Pistons travelling too far.
6. Bleed the calliper
7. Check for leaks.
8. Check lever travel.

Once he's ensured there are no leaks, and that the pads grip the rotor sufficiently to stop the wheel when the lever is squeezed - I'm struggling to see where the danger lies?

Graham

P.S. To the OP, good on you for having a go.

 

[goody]

There's danger around every corner - expect the unexpected.

 

[Yellow Saddle]

That's not my point, if the fault reoccurs when at high speed or in heavy traffic it could be a real issue. I have seen someone's brake fail to work and also suddenly jam full on, in both cases they were lucky.

If the sky falls then we're all in shoot too. Brakes just don't suddenly jam full on. That type of nonsense should be nipped in the bud. Perhaps if you were to tinker with stuff from time to time you would be able to predict a more plausible scenario for how a botched brake could fail. Sudden jamming it ain't.

 

[Yellow Saddle]

If the sky falls then we're all in shoot too. Brakes just don't suddenly jam full on. That type of nonsense should be nipped in the bud. Perhaps if you were to tinker with stuff from time to time you would be able to predict a more plausible scenario for how a botched brake could fail. Sudden jamming it ain't.

PS - I didn't say shoot. The system refuses to let me have free speech.

 

[tincaman]

Update:

Here's why the caliper wouldn't go back in, bearing in mind that originally I only pumped it out slightly, about 1mm, to try and reduce lever travel, it started leaking almost immediately.

 

[tincaman]

As its the rear I'm going to replace it with the 105 level RS505 caliper @ £32

 

[Tenacious Sloth]

Update:

Here's why the caliper wouldn't go back in, bearing in mind that originally I only pumped it out slightly, about 1mm, to try and reduce lever travel, it started leaking almost immediately.

Wow! I'm assuming the white gunk is the brake fluid contaminated by ingress of water?

The RS505 seems like a reasonable choice assuming it'll work properly with your existing levers?

I was thinking of upgrading the cable disc brakes on my CAADX with these but it's a lot of money with the 11 speed compatible levers.

Let us know how you get on.

Graham

 

[Yellow Saddle]

Wow! I'm assuming the white gunk is the brake fluid contaminated by ingress of water?

The RS505 seems like a reasonable choice assuming it'll work properly with your existing levers?

I was thinking of upgrading the cable disc brakes on my CAADX with these but it's a lot of money with the 11 speed compatible levers.

Let us know how you get on.

Graham

No, it is broken bits of ceramic. Those Shimano pistons are made from the stuff and not from resin like on the other brands. It seems that hard pressing at the wrong angle chipped the poor thing or it was just plain faulty.

Shimano systems don't use brake fluid (aka DOT fluid) but oil. Water ingress is clearly visible as, well, oil floating on water.

The ceramic piston is a response to Shimano's attempt to a) manage heat and b) reduce piston-scuff.

Keep on tinkering @tincaman .

 

[Levo-Lon]

Looks like poor poached egg effort..lol..fubared..
new brake is a good move..i dont think shimano sell parts piston and seal parts ...just new brakes

 

[tincaman]

Can't quite work out why it happened, there is no water in there, the seal is intact and undamaged. My fault for pumping it out slightly but it was not far enough to go past the seal. With all the meddling I did before I took it apart completely, it was reinstalled on the bike and working although out of position, I just wasn't happy with it. I was thinking next time I need new pads that they were never going to be able to be installed. I couldn't quite believe all the bits of ceramic when I took it apart.

 

[lpretro1]

And? Do you think the OP is stupid enough to not test them before using them? Also, doesn't he have two brakes on his bike? C'mon, stop this inquisitiveness-is-dangerous nonsense. Next you'll ask him to wear a hi-viz jacket when washing his bike.

The latter part of your comment is really stupid one to make my friend and singularly unhelpful. There is nothing wrong with inquisitiveness if you have some modicum of ability to deal with the consequences - the OP was asking for advice which was given with the sensible caveat 'if u know what you are doing' as I have no ideas what his mechanical abilities might be. My experience as a cycle technician trainer have shown that there are some people in this world who just do not have the ability to 'fettle' things and are just mechanically inept - I am not saying the OP is one of those of course as I do not know him Your constant digging at someone like myself it distracting from getting the guys brake fixed and I do not know what your motive might be but frankly it is irritating and unhelpful to the OP - if you want to have a dig at me do it as a PM