Vingleik Vaagal

Had an issue with my Ultegra hydraulic breaks when installing new break pads. Tried to push the pistons back to make room for the new pads, and pressure must have been too high and fluid came out from the chamber on top of the lever. Re-bleed the breaks, and they currently work but bubbles are coming out by one of the bolts. Anyone experienced the same? Possible to stop the leak without replacing the lever?

TimothyH

What bolt is leaking? Is it the filler screw at the top of the lever?

Is the little O-ring still on the screw? It is easy to loose track of.

Vingleik Vaagal

TThe far left of the mineral oil chamber ones.

TimothyH

Oh, then I don't know.

Maybe blew out a seal, but I really don't know. I'm staying tuned to hear the final resolution though.


-Tim-

Bill Kapaun

It may simply be a case that you displaced more fluid then the reservoir could hold when you pushed the pistons back. It has to go somewhere.
I don't do discs on bicycles, but have ran into that in the automotive realm.

fietsbob

non specific ( I only own Magura brakes) tightening the fittings compresses 'olives;, metal rings that grip the hose.

I have had no hose leaks ..





..

Metaluna

Yeah it sounds like something is seriously wrong. The bleed screw isn't even visible in the photo the OP posted (well it is, but just barely). If fluid or air bubbles are coming out from around one of the bolts pictured, then there must be an internal leak somewhere. I don't know anything about what the reservoir looks like internally, but maybe tightening those bolts might seal it up again. Here is the exploded view:

https://si.shimano.com/pdfs/ev/EV-ST-R8020-4245A.pdf

About the only places where you have a shot at fixing an oil leak would be the area around #4 or #9 (where the hose joins to the lever), because these parts are replaceable. Unless Shimano has a secret, dealer-only parts manual for their levers, everything else appears to be non-serviceable.

Vingleik Vaagal

Took it to my local bikeshop. Apparently it’s like a fail safe thing on the levers. Fluid will come out of pressure is too high. He inspected the chamber, sealed it back it (which I thought I’ve did), and it’s back up and running. Without a leak.

TimothyH

I am skeptical of that explanation.

Pressure when depressing the levers are as high, if not higher than anyone could ever exert when pushing the pistons back.

Maybe there is something I don't know about Shimano levers that explains it and I'd be interested to hear.

Either way, please proceed with caution and test really hard braking under controlled conditions before you descend down the side of a mountain.



-Tim-

Metaluna

When you depress the brake lever, the master cylinder closes itself off from the fluid reservoir before pressurizing the system. So the reservoir never sees the full pressure (over 1000 PSI, from what I've read) of the hydraulic lines, and doesn't need to be sealed against extreme pressure. In fact, you could leave the bleed screw off entirely and the reservoir wide open to the air, and the brakes would still work (for a while anyway, until enough air got in or fluid leaked out). Shimano's funnel-based bleed procedure wouldn't work at all if pulling the brake lever caused the reservoir to pressurize, for example.

When you reset the pistons, however, you aren't pulling on the levers, so the system is fully open and fluid can flow freely between the reservoir, master cylinder, hoses, and calipers. So I suppose it would be possible, if you push the pistons in far enough, to force enough fluid back up into the reservoir to over-pressure it. I guess it's plausible Shimano could have designed in some kind of relief valve to prevent damage to the reservoir seals if that happens. Or possibly some fluid just leaked past one of the seals, but didn't permanently damage it, so it just closed back up once the pressure was removed.

Totally agree!

tayguer

Shimano reservoir seals are not very strong and over pressurization will easily cause what is described here. Try using a syringe at the lever (not recommended) and you'll see what I mean. As noted, the reservoir is closed off during braking action. Great explanation above.

I could see this happening if one were to bleed the brakes without resetting the Pistons. The system would have too much oil volume for the Pistons to retract all the way.

TimothyH

I stand educated and am in your debt.

Just like an automobile. Pushing back the pistons on an auto caliper and I'd expect the cap to blow off the reservoir if it had not already been removed.

Very good. Thank you.

Disregard post number 9.


-Tim=

arctic84

I'm experiencing the exact same issue here, should have cracked open the caliper bleed valve when i was resetting the caliper. Pressed far too hard and heard a sound like a small plastic pop and hiss, to find fluid on the floor because my bike was also upside down since i was working on it. Pretty sad.. shimano doesn't seem to sell the seal either..

It's pretty clear when I press the lever that oil comes out through the crevice.

There's a large rubber seal covering the chamber. Not sure if it's really pressure relief or if I popped the seal but each time i checked back it still was spewing small bits of fluid out

bigredgrad01

I am having this exact issue after pushing in pistons when replacing the brake pads (as manual instructs to do).

"Use a flat-shaped tool to push the
pistons straight back in as far as they will
go, while being careful not to twist the
pistons.
Do not push the pistons with a sharp
tool.
The pistons may be damaged."

The way it manifested is that some time after changing pads, the lever went soft, and I noticed a drop of fluid under the cover. Lever would get hard after some pumping, but would go soft again.
Today I bled the brakes, and the lever was initially nice and firm, but then went soft again. I checked again under the hood and found this leak on the side of the lever, and also this bubbling when squeezing brake.
It looks like this video I found:
And is apparently a common failure. They should either build in some failsafe, or warn people to open bleed valve when pushing piston.
I bought my bike new less than 2 years ago, so hopefully Shimano warranty covers it, will be contacting them directly tomorrow.
Anyone deal with them directly on OEM parts pre-installed on bike? I don't want to go to the bike store due to COVID.

Troul 

the speed in which "pushing" in the piston is not fool proof. It has to be done not only carefully, but gradually. Once it is where it needs to be, it's time to reinstall or replace the pads & back over the rotor at a steady pace. Once the brake caliper is bolted in place, slowly & fully squeeze the handle & guide the hand back to rest at the same speed. With another like squeeze & release, note the feel. If it is continuously firm, try rolling the bicycle with your weight on it. If the brakes are able to hold you from moving, it should be ready for use. If the brakes enable movement, you may need to purge some air out.

Caretta

There is a rubber seal/bladder behind a plastic cover fastened with 3 T8 on "the inside" side of the lever. Probably this causing problem, it is possible to exchange to a new, done in 5 min.

Atlas Shrugged

Don’t worry about it happened to me about 5,000 km ago. If the reservoir is full and you push the pistons open you get some displacement.

Turkishadam

have you done this and where did you get the new bladder from? I have this problem. The rubber bladder is torn but shimano apparently do not sell this part as a spare.

Caretta

Did it on a 7020 shifter, had a broken shifter that served as a donor.
I think its sad that shimano doesnt carry it as a spare since its possible to replace, but as someone mentioned earlier, you might not need to replace it?

Turkishadam

defo need to replace, the bladder has split. Have now bought a new lever but am keeping my eyes open for a broken shifter to use for parts. Everything is few and far between at the moment though. It is bad that such an easily replaced part renders the shifter useless. Bad design in my thoughts.

Soussef24

I found a spare part catalog, where that part seems to be now listed as a "Diaphragm" with part numbers for Right Y0C678000 and LEFT Y0C578000.

The part is the same for a lot of models, Tiagra, 105, Ultegra, Dura-ACE, GRX... And the document is recent (June 2021). Unfortunately, I cannot post the link or a screenshot yet (I need to have 10 posts on the forum before).

But I still cannot find it anywhere online. Hope it'll be available soon...

Thanks.

Pacopukas

En AliExpre
Shimano-palanca de Control de diafragma de aceite, disco Dual, ST-

Pacopukas

Tengo el código completo para AliExpress pero no puedo añadir no me dejan el Foro

Pacopukas

Acabo de comprar en AliExpress. Yo tengo el mismo problema con el freno derecho

Pacopukas

¡Ayúdame a escoger!
€ 11,05 | Shimano-palanca de Control de diafragma de aceite, disco Dual, ST-4720/R7020/R7025/R8020/R8025/R9120, Y0C678000 Y0C578000 Y0C598030 Y0C698060

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