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Shimano R8020 - Leak

Old 07-01-19, 01:03 PM
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Vingleik Vaagal
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Shimano R8020 - Leak

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?
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Old 07-01-19, 01:15 PM
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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.

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Old 07-01-19, 01:27 PM
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TThe far left of the mineral oil chamber ones.
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Old 07-01-19, 02:08 PM
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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.


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Old 07-01-19, 06:38 PM
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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.
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Old 07-01-19, 09:32 PM
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non specific ( I only own Magura brakes) tightening the fittings compresses 'olives;, metal rings that grip the hose.

I have had no hose leaks ..





..
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Old 07-02-19, 11:18 AM
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Originally Posted by TimothyH View Post
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.
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.
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Old 07-03-19, 05:26 AM
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Took it to my local bikeshop. Apparently itís 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 Iíve did), and itís back up and running. Without a leak.
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Old 07-03-19, 12:36 PM
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Originally Posted by Vingleik Vaagal View Post
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.
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.



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Old 07-03-19, 01:42 PM
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Originally Posted by TimothyH View Post
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.
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.

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

Last edited by Metaluna; 07-03-19 at 01:45 PM.
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Old 07-03-19, 02:37 PM
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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.

Last edited by tayguer; 07-03-19 at 02:43 PM.
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Old 07-03-19, 05:16 PM
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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=
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Old 06-30-20, 12:53 AM
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Same issue here

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

Last edited by arctic84; 06-30-20 at 01:00 AM.
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