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Recently I had an accident on my bike, and my front brake 11-speed, front brake GRX 600 shifter isn’t braking well anymore.

The shifter took a bit of damage in the fall. Initially it didn’t shift, and I had to bend the edge of the lever arm (under the “X” of the GRX logo) outwards to stop it fouling on the inner shift lever. Shifting is fine now 🥳, but there are problems with the hydraulic brake.

GRX shifter with damage after crash

The brake seemed fine. Pulling the lever it feels firm and brakes confidently. The problem is that the brake power fades and the longer you pull the lever the more it pulls in to the handlebar. Over a fairly short descent the lever can be pulled past the bar and the pads aren’t pressing on the disc anymore. Releasing the lever and squeezing again gives another firm/confident brake, which then eases off again.

My first thought was that this is a bleeding issue, so I picked up a bleed kit and gave it a go. This didn’t solve the problem, so I went through the bleed process again, to no avail.

There’s a good chance I’ve just failed to bleed it correctly. The handlebars are ridiculously aggressive gravel bars, so rotating the shifter to the correct position to “burp” it was a challenge. Also, I noticed a few tiny bubbles in the syringe of mineral oil (it was new).

Do the symptoms above sound like a bleed issue, or something else? All the advice I’ve found on the internet about air in the system and bleeding seems to suggest braking will be spongy but “pump up”. That’s not what I’m experiencing.

It’s seems impossible to get hold of Shimano GRX components at the moment, so I’m really keen to fix this even if it just holds me over until it can be replaced.

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    Is there an oil leak anywhere? Did the bleed improve the situation or make it worse? The only ways I can think of explaining this are 1: the seal in the master piston failed, or 2: there’s an oil leak.
    – MaplePanda
    Commented Mar 24, 2021 at 19:15
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    Sounds like the piston in the lever has a leaking seal.
    – Daniel R Hicks
    Commented Mar 24, 2021 at 21:15
  • Is the fade happening under braking that "should" be within the brake's capabilities or was fine before the crash?
    – Nathan Knutson
    Commented Mar 24, 2021 at 21:59
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    Also, pulling the lever when you're standing still, is there a "staged" feel to it where you squeeze it moderately and it seems okay, but then you squeeze it hard and the lever sinks to the bar with an almost springy, elastic feel?
    – Nathan Knutson
    Commented Mar 24, 2021 at 22:10
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    Piston seal leaking back into the reservoir would cause this with no oil leak. May have bent the shaft so its putting uneven pressure on the piston. Air in the system - which is why you bleed is different - lever is spongy and its travel does not change with time (but may change with pumping).
    – mattnz
    Commented Mar 25, 2021 at 2:20

2 Answers 2

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The symptoms you are describing seems to be a "Ghost Leak" - Rides of Japan terms it this way. It might actually just be a kink in the hydraulic hose.

His symptoms are similar. Squeezing the brake feels powerful, but holding on to it will eventually cause the hydraulic pressure to release. Once he lets go of the brake lever, and squeeze it again, he can feel the power again.

Definitely recommend you checking out Rides of Japan's recent video on this, it's quite in-depth as he shows why it happens.

In short, over a period of time, the points where the hydraulic hoses get kinked will wear out over time. Especially if there are accessories like handlebar bags there actually slightly re-route the hoses' entry into the frame/cable guide. As the hoses are under pressure from the hydraulic fluids, eventually the inner lining will disintegrate, causing a kink.

In your case, could it be that the hoses actually got hit in the accident? It might be ideal to replace the hoses too! If really there's a kink in the hose, it won't be apparent from the outside too.

Rides of Japan is quite thorough for this issue (for a home-mechanic at least), it's easy to understand from his documentation! Hopefully, this is the correct approach to your issue, good luck!

P.S. I mentioned Rides of Japan like 3 times, but damn it his videos are binge-able!

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    I understand many comments read that there might be a fault in the sealing. To me, if the seal faults, it won't be possible to regain the hydraulic pressure for you to be able to feel the pressure in the next squeeze. But who knows! Always worth to try everything :)
    – Yuxuan
    Commented Mar 25, 2021 at 2:45
  • That’s frickin’ genius, I never even thought of that!
    – MaplePanda
    Commented Mar 25, 2021 at 6:03
  • @Yuxuan it may be the system leaks only when a certain pressure threshold is released. So when you drop the pressure, releasing the lever, the system seals itself again, so for the next squeeze of the system, pressure ramps up, open the seal, the leakage starts ... repeat until enough hydraulic fluid leaked out of the system and no pressure can be applied.
    – EarlGrey
    Commented Mar 26, 2021 at 10:24
  • This is a great video, and thanks for the suggestion @Yuxuan 🙌. Those symptoms look similar, just a bit slower on my brakes. My hoses look pristine (they're only a couple of months old), but I'm going to test the theory by swapping the levers (only on the stand!). That'll tell me if it's the levers or the rest of the system. Thanks!
    – spikeheap
    Commented Mar 26, 2021 at 11:19
  • Cheers @spikeheap! That sounds like a great idea! Be sure to ensure the brakes are bled after the swap. Honestly it's hard to pinpoint any one root cause, due to the plethora of complexity that hydraulics bring, but please do give an update on your issue if you may. I definitely wish to learn more about this issue!
    – Yuxuan
    Commented Mar 29, 2021 at 3:52
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I experienced the same issue. What I found was the pistons don't extend and retract equally. Over time one pad wears more than the other which creates uneven spacing between the pads and rotor. Recenter the pads so the gap is equal. Also found the GRX brakes don't self-adjust so I insert a feeler gage that is thinner than the rotor and pump the levers to reduce the gap. Perform both actions and the issue goes away (until next time)

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