Shimano GRX bleeding issue- Mtbr.com
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  1. #1
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    Shimano GRX bleeding issue

    I can't seem to get a good bleed on my front grx 800 brake. The group came with a quasi quick connect in the middle which is not really a quick connect. I can get an initial good bleed with good stroke but after 24 hours it all goes to crap. I thought maybe that barrel adaptor in the middle of line has a leak but can't find it. Do I just need to get rid of the middle barrel adapter altogether and go full hose from end to end?

  2. #2
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    Did you make sure the oring was on the cap in the lever? How old are your pads?
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  3. #3
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    Quote Originally Posted by DDRP Anchorman View Post
    Did you make sure the oring was on the cap in the lever? How old are your pads?
    The whole group is brand new. It's the ones that come pre-bled from the factory but of course I had to shorten hoses. So I shortened the hose on the caliper to barrel connector side and left it alone on the sti to barrel side.

  4. #4
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    Quote Originally Posted by gus6464 View Post
    I can't seem to get a good bleed on my front grx 800 brake. The group came with a quasi quick connect in the middle which is not really a quick connect. I can get an initial good bleed with good stroke but after 24 hours it all goes to crap. I thought maybe that barrel adaptor in the middle of line has a leak but can't find it. Do I just need to get rid of the middle barrel adapter altogether and go full hose from end to end?
    I would personally go full hose (I've even always done that for derailleur housing). Can you post a pic of the barrel connector? Mine didn't some with such a creature...

  5. #5
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    I had similar issues on my RS405 brakes, the problem on my case is that I had not tipped the bike nose down during the bleed process so I still had some air in the system. Once I learned that the bike had to be tipped nose down I got all the air out and the brake were fine. I had/have the quick connector too. The conector was not the problem. Once I upgraded to GRX the process was the same.

  6. #6
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    If you follow Shimano’s bleeding procedure 100% you will get a good bleed.

  7. #7
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    I've had the same problem, but also don't think I've been doing nose down. Also, I'll cke out Shimano's bleeding procedure.

  8. #8
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    That's really weird, if it was good initially but not 24 hours later, it's gotta be a leak somewhere.

  9. #9
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    Quote Originally Posted by klatekin View Post
    That's really weird, if it was good initially but not 24 hours later, it's gotta be a leak somewhere.
    The good one moment, soft the next, usually is bubble(s) stuck in master and is more common on rear and usually manifests for me when bike gets inverted or really tilted and the bubble works its way out of master into the line.
    Do the Shimano method which involves tilting the lever/master up and down. And the lever flick is usually the fibal thing that gets it all out.

  10. #10
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    Word of warning with Shimano GRX brake bleeding: When removing or installing the bleed screw, be VERY careful. Being plastic, the threading on the housing strips VERY easily - resulting in an expensive replacement of the whole shifter. Very poorly engineered.

    (In the event a warranty claim isnt an option, I'm thinking a helicoil *might* work as a fix.)

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  11. #11
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    Well for an update turns out my bleeding procedure was not the culprit but instead there was an issue with both brakes.

    Over the past couple of months my bike was loosing pressure on both the front and rear brakes. Got tired of trying to re-bleed so ended up taking it to my shop.

    They had to take everything apart but found out that the rear caliper was leaking at the pistons and the front had a leak in the master cylinder at the shifter.

    To Shimano's credit though the shop called them and they had a brand new left shifter, caliper, and brake pad arrive the next day and got it all installed. Seems I got lucky that they even had the part because the US warehouse is empty with no restock until March 2021 they said. But I am running the GRX 800 left dropper post type shifter which is not that common so they had plenty of those.

    Also my shop said that the first batch of GRX800 stuff seems to have a leaking problem which is why Shimano replaced everything no questions asked.

    So everyone check your GRX 800 stuff for any leaks...

  12. #12
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    After about 9 months on my GRX800 setup, I just noticed my front brake had gone soft. Bleed was clean and easy, and I had that classic grey, cloudy fluid when I drained the system. Hoping it was just nasty, contaminated fluid and not a leak. I've dealt with leaky shimano mountain brakes, usually a leak at the caliper is obvious as it gradually contaminates pads and rotors.

  13. #13
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    I had a set of GRX calipers develop leaks both front and rear. Seems like there might have been a production issue on that early run. Replacements have been fine so far.


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  14. #14
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    Dangit. I'm glad I saw this thread because my rear/right kept getting soft, even after 3 full bleeds. Is it pretty obvious if the caliper is leaking?
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  15. #15
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    Quote Originally Posted by Drevil View Post
    Dangit. I'm glad I saw this thread because my rear/right kept getting soft, even after 3 full bleeds. Is it pretty obvious if the caliper is leaking?
    It's usually very slow leak. If it keeps getting soft it's most likely leaking at the piston.

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  16. #16
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    Quote Originally Posted by Drevil View Post
    Dangit. I'm glad I saw this thread because my rear/right kept getting soft, even after 3 full bleeds. Is it pretty obvious if the caliper is leaking?
    My rear failed suddenly and wouldn’t retract during a ride. Front was a slow leak that would contaminate pads over a a few rides.


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