Shimano RS785 caliper

tincaman

I have been playing with the rear caliper trying to reduce the lever travel, but unfortunately made the onboard piston pop out too far which then started leaking from the piston. The trouble is that I can't get the piston to go back in far enough, I have drained the system down and taken the caliper off, stuck a tyre lever in there but it just won't go back in. The other piston goes in almost flush but this one sits out about 2mm, if you reinstall everything it works ok but now the caliper is off centre so I can't get it not to rub the disc. It's not the pads rubbing the disc, it actually the disc rubbing the caliper itself.
Any ideas how to get that piston back in properly?

tincaman

Well I took it all apart and here's why the piston wouldn't go back in:

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.

852Kompol

Did hear of the RS785 ceramic piston issues with Shimano before when BR reviewed it(Cracked) when it first came out, Try contact Shimano see if they can replace it for you I guess?

bikingjohn

I made mistakes in bleeding the RS785 and RS505.

I applied too much pressure during the bleeding, then the oil started to leak through the piston (the seals popped?), and it could be bled properly and keep leaking.

I tried to open the calipers but I got now vice and can't unscrew the star screws.

tincaman

Update:
Ordered and fitted the T675 caliper@£21 and it works really well, I actually have less lever travel than before which is all I ever wanted.
The differences are:
The pads are different to the front,
You have to take the wheel off to get the pads in,
The securing pin is just a split pin instead screwed in.

dgunthor

tincaman wrote:

Update:
Ordered and fitted the T675 caliper@£21 and it works really well, I actually have less lever travel than before which is all I ever wanted.
The differences are:
The pads are different to the front,
You have to take the wheel off to get the pads in,
The securing pin is just a split pin instead screwed in.

you can always use a tap to thread the hole then use a standard pin

tincaman

You know what, I'm going to do that!