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  1. #1
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    Brand new SRAM Guide RSC pistons slow to return?

    I just mounted two brand new sets of SRAM Guide RSC brakes to my cross-country bike. These are the latest version (with the Bleeding Edge port on the calipers). I trimmed the lines and bled them with the Sram Pro kit.

    I'm using Shimano Icetech rotors (180 F, 160 R) with the Shimano adapters. I checked the rotor/pad spacing and after some re-spacing, the top of the pads seem to align with the top of the rotor.

    The rear brake is all good, but the front brake pads/pistons seem to return slowly. On the first ride today, the front brake would sometimes/intermittently make a scraping or turkey wobbly noise after releasing the lever, but this noise would go away on it's own after riding for 10-20 seconds or so.

    The power and lever feel in both brakes is really good. The levers are smooth and provide snappy return. And the rear brake doesn't have this problem.

    What do you think I should do to stop the intermittent short-term noise after releasing the front brake?

    Many thanks!

  2. #2
    WillWorkForTrail
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    Pull the front caliper and remove the pads. Work the pistons out, lube them, push them back in, and see if that helps.

  3. #3
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    First thing I'd do is make sure the rotor is true and the caliper is properly aligned with pads equally spaced from the rotor. Squeezing and holding the lever and tightening the caliper mtg bolts often works, but not always. Sometimes you have to eyeball it and manually adjust the caliper. What cotharyus suggests could help, but normally you don't need to do that on new brakes.

    Also, bleed with the bleed block to ensure there's not excess fluid in the system, which can cause brakes to drag, or drag when the heat up.
    Do the math.

  4. #4
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    Good advice, Cotharyus, thanks. I never thought I'd need to do this to new higher-end brakes!

  5. #5
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    Quote Originally Posted by Lone Rager View Post
    First thing I'd do is make sure the rotor is true and the caliper is properly aligned with pads equally spaced from the rotor. Squeezing and holding the lever and tightening the caliper mtg bolts often works, but not always. Sometimes you have to eyeball it and manually adjust the caliper. What cotharyus suggests could help, but normally you don't need to do that on new brakes.

    Also, bleed with the bleed block to ensure there's not excess fluid in the system, which can cause brakes to drag, or drag when the heat up.
    Thanks for the good advice Lone Ranger. I've done the caliper alignment, used the Hayes tool, business cards, extra shims, squeezed the lever, released a bit of fluid from the reservoir, all the usual tricks.

    When I squeeze the lever with the pads out, both the inboard pistons move out about 3 mm or so while both the outboard pistons only move out maybe 1 mm or not even. Is this normal?

  6. #6
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    And FWIW, Shimano rotors are thicker than SRAM rotors. Just sayin’...

  7. #7
    WillWorkForTrail
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    Quote Originally Posted by pktrain View Post

    When I squeeze the lever with the pads out, both the inboard pistons move out about 3 mm or so while both the outboard pistons only move out maybe 1 mm or not even. Is this normal?
    This is exactly the sort of thing my initial advice is meant to take care of. Unfortunately, it looks like some (all?) Guide brakes are being assembled without enough lube on the pistons to ensure that they all move at about the same amount of internal pressure when activated.

  8. #8
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    Quote Originally Posted by Cotharyus View Post
    Pull the front caliper and remove the pads. Work the pistons out, lube them, push them back in, and see if that helps.
    Quote Originally Posted by Cotharyus View Post
    This is exactly the sort of thing my initial advice is meant to take care of. Unfortunately, it looks like some (all?) Guide brakes are being assembled without enough lube on the pistons to ensure that they all move at about the same amount of internal pressure when activated.
    This. Just grab a q-tip and swab away with some iso, then lube it with brake fluid (ie. wet a q-tip swab around) and rinse repeat until the pistons move freely.

  9. #9
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    Quote Originally Posted by thesmokingman View Post
    This. Just grab a q-tip and swab away with some iso, then lube it with brake fluid (ie. wet a q-tip swab around) and rinse repeat until the pistons move freely.
    This sounds good, thanks!

  10. #10
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    Quote Originally Posted by farfromovin View Post
    And FWIW, Shimano rotors are thicker than SRAM rotors. Just sayin’...
    Good point. And my Icetech rotors are impossible to true, which from searching this forum seems to be a commong problem...

  11. #11
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    Quote Originally Posted by pktrain View Post
    Good point. And my Icetech rotors are impossible to true, which from searching this forum seems to be a commong problem...
    For example, every time I braked hard with my Saints and ice tech rotors they’d rub for 5-10s. However, the Saints never rubbed on my Centerlines. I believe it’s 1.8mm for Shimano and 1.7mm for SRAM.

  12. #12
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    Had this exact issue with Code R brakes, i know not the same as your's but close enough

    Did the brake fluid on pistons till they worked in and out smoothly with a tire lever, but when I threw them on the bike, the pistons wouldn't return.

    Took them to an LBS and LBS sent them back for warranty- something about the seal behind the piston not allowing them to move back

    Its been about 1.5 weeks, but hoping to get them back soon to see if a new brake has the same issue

  13. #13
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    Quote Originally Posted by farfromovin View Post
    For example, every time I braked hard with my Saints and ice tech rotors they’d rub for 5-10s. However, the Saints never rubbed on my Centerlines. I believe it’s 1.8mm for Shimano and 1.7mm for SRAM.
    Quote Originally Posted by ehfour View Post
    Had this exact issue with Code R brakes, i know not the same as your's but close enough

    Did the brake fluid on pistons till they worked in and out smoothly with a tire lever, but when I threw them on the bike, the pistons wouldn't return.

    Took them to an LBS and LBS sent them back for warranty- something about the seal behind the piston not allowing them to move back

    Its been about 1.5 weeks, but hoping to get them back soon to see if a new brake has the same issue
    Thanks for the good info here...

    I seemed to have (hopefully) solved my problem. I pulled the pads, squeezed the brake lever to expose 4-5 mm of piston, really doused them with DOT 5.1 fluid with a Q-tip, and pushed them in with a tire lever. I repeated this maybe 12-15 times for a good half hour until they improved. It took a while, just kept moving the pistons in and out and dripping DOT fluid on them each time.

    I also swapped out my Icetech rotors for Centerlines.

    I mounted everything, stand tested, then test rode down the driveway and everything appears to be working now with no problems. Hopefully it holds up on the trail.

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