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GRX brake pressure issue

2351 Views 5 Replies 4 Participants Last post by JustScott, Feb 15, 2022

JustScott

Discussion Starter · Jan 17, 2022

Hi all - any idea what could cause this type of brake issue - I've tried multiple bleeds to no avail - the symptoms are that if I pull the lever normally/quickly, it works fine, but if I pull it slowly (or pull it half way and then pause and pull the rest of the way) - it goes all the way to the bars with no pressure. Since on a downhill I sometimes feather the brakes, this causes them to fail to work every few pulls - very annoying. I assume this is some sort of issue inside the lever or caliper where something works when pressure is applied quickly but not if applied slowly - but I don't know the ins and outs of hydraulic brake design so not sure if that's possible or what it would be. Gonna take it to the shop and see what they think, but in the meantime - any ideas?

Video demo of the issue:

Thanks,
Scott

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245044

· #2 · Jan 18, 2022

These levers have a more complicated bleed procedure than a lot of brakes out there. Not sure why, but Shimano has a detailed bleed procedure for the GRX/road levers which includes lever angle changes and pressure and gravity bleeding. Assuming you followed the correct procedure, sounds like maybe a lever issue.

Good luck.

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JustScott

Discussion Starter · #3 · Jan 18, 2022

mopartodd said:
These levers have a more complicated bleed procedure than a lot of brakes out there. Not sure why, but Shimano has a detailed bleed procedure for the GRX/road levers which includes lever angle changes and pressure and gravity bleeding. Assuming you followed the correct procedure, sounds like maybe a lever issue.

Good luck.

Thanks - yeah, unfortunately I have made numerous bleed attempts following the suggested procedure with all the angle changes, etc...

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bryanc

· #4 · Jan 19, 2022

Have heard reports of internal seal problems in the GRX brake levers. Contact Shimano CS and see what they have to say about it.

I had something similar happen to mine but a good bleed took care of it. Some people have had to replace the levers. The 815 levers are pretty hard to find right now, so getting a replacement may be difficult.

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Taroroot

· #5 · Jan 22, 2022

Yeah, I was going to say sounds like a seal issue where the lip of one of the pistons, the mc side in lever, is leaky. Pull rapidly and it pushes the lip out more and it seals, slowly and the lip doesn't seal.

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JustScott

Discussion Starter · #6 · Feb 15, 2022

Thanks for the suggestions about the brake lever seals - turns out that was the issue. I got a new brake lever (sent the old one back to Shimano for warranty claim) and it works fine.

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