Have a leak bleeding road hydraulics - Shimano RS785

[merlinmurph]

OK, so I decided to bleed my brakes for the first time on the Seven Evergreen, hoping that the lever would end up with less travel. Got a bleed kit, fluid, etc. and gave it a shot today.

Well, I barely got started when I hit issues.

After taking the pads out and putting a brake block in the calipers, I squeezed the lever and it bottomed out. Huh? Then, I saw fluid dripping off the caliper. I did this a few more times, trying to figure out where the leak was. It looked like that maybe, maybe, there was fluid coming out from around one of the pistons. Hard to tell. Is that possible? How?

The night before, I tested things out and found the brake block didn't fit, so I shaved it down a little. I put it in, squeezed the lever, and things worked great. Today, I have leaks.

Thanks,
Murph

[vqdriver]

i haven't worked on that specific set up, but i've bled mtb bikes plenty.
from my experience, if the block fit is tight (assuming it's a shimano block included with shimano brakes or bleed kit), i push the piston back with a plastic tire lever, not shave the block. fwiw, those pistons don't have to have a whole lot of travel, even a half mil or so on either side can be enough.

[merlinmurph]

if the block fit is tight (assuming it's a shimano block included with shimano brakes or bleed kit), i push the piston back with a plastic tire lever, not shave the block.

I actually tried that first - no luck.

[sales guy]

There are two different brake blocks for SHimano calipers. One slightly thicker than the other. They look identical tho.

As for a problem in leaking around the piston, yeah, it's totally possible. The piston is ceramic and they have had them crack before. It's not like a 1 in 10 number. But it has happened.

Drain the system completely and pull the piston. You might have a crack in it. If not, check the seals and see if there is dirt or debris causing a problem. But yeah, this is totally possible.

[tigoat]

No, how can the lever bottom with the block in the caliper? That is not possible, as the block should be a tight fit. Most of the time I have to kind of force the block into the caliper so there should be virtually zero travel. The fluid is leaking through the pistons, as once the travel pass a certain limit, it just opens up. I think no harm was done. Just push the pistons back in, drain the fluid completely and re-bleed the system.

[bigbill]

I've got 785's on my gravel bike. The block that came with the caliper just slid in and I needed the pin to keep it in place. I had to install the entire system then fill and bleed the brakes. The only way the lever could bottom out with the block installed is air in the system or a leak at the line connection which would also get air in the system. Do you have the threaded cup for filling the system? If so, push some fluid up from the caliper until you get a level in the cup and then bleed it back to get the air out. Should get the lever range of motion back.

FYI, the instructions said to set up with the lever "in" for short reach and then adjust outwards if needed. I set my bike up to ride in the drops so I kept the short reach to two finger brake and shift.

[merlinmurph]

Yes, the lever bottomed out with the block in the caliper, but that was when it started the leaking. The question is, why did it start leaking? The brakes were fine up to that point.

My guess is that I broke something, like caused the piston to crack, by trying to push the piston in. I kept playing with it, until finally all the fluid seemed to leak out.

Brought the bike into my LBS this AM with my tail between my legs.

Good thing it's 20 degrees out and windy right now.

Thanks for the input,
Murph

[crankles]

I had a similar issue. ...turns out mine had developed a small leak at the lever.
Shimano replaced it under warranty.

[livingminimal]

785s had an issue with pistons cracking prematurely and due to irregular use (pushing pistons back in with a tire lever for instance). Ive replaced a couple of calipers so far under warranty.

[crankles]

785s had an issue with pistons cracking prematurely and due to irregular use (pushing pistons back in with a tire lever for instance). Ive replaced a couple of calipers so far under warranty.

This was my riding buddies problem...forgot to mention that as a possibility too.

[Gummee]

Shimano replaced it under warranty.

this

M

[merlinmurph]

785s had an issue with pistons cracking prematurely and due to irregular use (pushing pistons back in with a tire lever for instance). Ive replaced a couple of calipers so far under warranty.

No kidding? That's the only thing I can think happened.

Thanks,
Murph

[CiclistiCliff]

Maybe you shaved the block unevenly, causing one or both of the pistons to contact at an angle and jam in the bore.

I've seen it happen with brakes whose pads were worn to the backing plate, yet Shimano has been generous enough to warranty.

[merlinmurph]

Maybe you shaved the block unevenly, causing one or both of the pistons to contact at an angle and jam in the bore.

I've seen it happen with brakes whose pads were worn to the backing plate, yet Shimano has been generous enough to warranty.

Yup, that's very possible - thanks!