Anyone know anything about disc brakes?

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  • My 105 R7020 levers from my Giant have always had a lot of travel to engage the brakes, to the point to having to pull the levers right up to the handlebars to fully engage. I've not ridden much the past year to really worry about it, but this past weekend in the wet going down Crystal Palace I was conscious I pulled the levers all the way to touching the bars and I was not getting the stopping power I do with my Tiagra RS505s.

    I figured I just needed to bleed this as normal to get any air out so I went through the steps I always do. Feed mineral oil through caliper to fill up reservoir at levers. Then have a tube and bag at open up caliper while pulling on lever to push out air. I did this four times, filling the cup to the top and getting it to 1/4 full before topping up and repeating. I tap along the whole system to move air around till the lever feels tight, the close everything up. Put the brake pads back in, put the red spacer in and press the caliper to get the spacing right. At this point, the lever goes back to all the way to the lever again.

    Is there something broken, or am I missing something?

  • Possibly leak?

    Another way to make sure to reduce bubble is to put the cup on the levers, fill it with a bit of oil and start squeezing the brakes (don't need to do proper bleed), small bubble should start appearing the more you do thi.

    Put the cover on the cup and you can shake the bike properly, bang a hammer on the bike stand to send vibration also.

    The biggest issues sometimes it's not the bleeding, it can simply be the calipers, I swapped calipers on customers and my bikes and it usually make a big difference.

  • New pads? If you're using the old pads, then bleed block width > pads + red spacer width. So the first few lever squeezes you'll just be pushing the pistons out to the correct place.

  • I'll give it a bash this evening after work, hopefully some gentle tapping will do the trick. Hopefully no need for new calipers

  • New pads, as that was my thinking as well. I bleed the put in new pads and it's just as bad as with old pads.

  • Silly question, but you put the yellow bleed block on right, and not doing this will pads still in?

  • I do, but more to prevent pads contamination.

  • Did as you recommended, saw one little bubble come up, and the level travel is much less with the block in. Put the top cap back on, bounced the bike up and down and taped the stand with bike back on. No more bubbles, but still the long lever pull when everything is put back together.

    One thing I noticed is one piston is moving further than the other, could this also be part of the problem?

  • Checked the rotor for wear?

  • Back off the pistons, center the brake. Shouldn't be a problem anyways unless one it's not moving

  • Right, I'm at my wit's end. A few weeks ago, my Di2 Hydro (R8050?) brakes had really long travel, as metioned above, but it got worse. Possibly caused by two train trips when the bikes were hung up for 3hrs by the front wheel.

    Rear has been a bit funny since I switched to a new bike in particular the lever not returning all the way back to the correct position after braking. To eliminate a kink in the hose, I replaced the hose, cleaned the caliper/pistons and tried to re bleed it. Oil will flow top to bottom, but I can't get it to flow from a syringe up to the shifter.
    It suddenly popped and oil flew out bleed cup, then filled normally. But as I proceeded with the bleed (gravity etc) the shifter wasn't getting firm. So I tried again and I can't get anything through the system with the syringe. If I pull the lever, it pushes oil out the caliper, so it goes one way.

    Is my very expensive and out of stock shifter F&*ked? Is there any way to try and flush out the lever to clear the blockage?

    Added a pic, the upper silver bar that I think connects to the master cyclinder doesn't go all the way to the right. It does on the other shifter.


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    • Screenshot 2021-07-02 at 15.48.09.jpg
  • but I can't get it to flow from a syringe up to the shifter.

    Have you tried with the lever pulled to the bar? with an elastic band or something

  • Just tried it. Still nothing getting through at all.

  • I'd check your connections to the lever and caliper, maybe you squished the olive funny when changing hose.

  • I'll check, but the issue with the lever not returning was happening before the hose change. I removed the old (3 months) one to check it. It was fine but I had to cut off the olive to get it through the frame so it was too short to re use.

    It seems like there is a return valve that it blocked or just gone. The free stroke adjustment screw doesn't seem to move the lever at all if that is a clue.

  • Shimano free stroke doesn't really do anything. Initial problem sounds like sticky pistons, especially if the not returning kinda feels like it "stacks" like the more you pump it the less it returns or it returns very slowly. Not returning at all consistently could be a problem in the lever, a seal blown or something, I've not stripped one down to repair but might be worth it if you're not paying someone workshop rates to try. Fluid not passing at all could be the same thing if it's a seal or something like the common problem with SRAM guides, or maybe a new problem introduced with the new hose, worth checking.

  • Can you hook it up to your other caliper to at least eliminate the caliper and hose being the issue?

  • When oil blew out of the bleed cup, did you see it come out of the cup? It sounds like the over pressure valve.

    Just to check, are you doing the bleed as per Shimano’s instructions? It’s late and I might be mistaken but I thibk the procedure if: bleeding bottom-up until no more bubbles, remove bleed cup, seal shifter, pull brake lever all the way and hold to the bar, gently repressurise with syringe while slowly allowing brake lever to release, do not add excess pressure with the syringe it should move the lever all the way out and feel firm and that’s all, seal calliper, test.

  • Interesting. Yeah it definitely came out the cup. After that I was initially able to feed liquid from the calliper to the lever. At the start there were loads of micro bubbles, frothy almost. Then it got better.

    I bled (or tried to) as per the shimano R8070 dealers manual. Fill from the bottom, gravity bleed to remove bubbles, depress lever and open/close valve on the calliper quickly. Oil in cup and pump lever, moving bike angle and tapping everything to get bubbles out.

    That wasn’t doing much so I started again and no oil would pass through the system.

    I have tried loads since and it looks like I can’t even gravity fill/bleed with a cup at the top. I even left it overnight with a full cup and the hose disconnected at the calliper. Nothing left the cup. But if you pull the lever, oil comes out the hose at the bottom.

  • Fluid can only flow between the reservoir/cup and the lever cylinder when the lever is in the fully relaxed position. If you push the lever away from the bar does the "blockage" disappear?

    Diagram here. The bleed cup hole is on top of the reservoir:
    https://en.wikipedia.org/wiki/Hydraulic_­brake#/media/File:Hydraulic_disc_brake_d­iagram.gif

  • I don't think so, but I will check. I think that is the basis of the problem though, even when I manually push the lever back, the piston it's attached to doesn't fully reset.

    On the attached pic, the good lever rests with the silver bar at A and moves to around B when using the brakes. On the bad lever it only ever goes back to B and moves to C when braking.
    I can't physically push it back any further.


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    • Screenshot 2021-07-04 at 10.29.49.jpg
  • I managed to force the oil through again and it kind of pushed the lever back a bit. Still wasn't gravity bleeding. I then took the lever off the bars altogether and the play in the lever went away. I was also able to gravity bleed with the lever off the bar. I let a load of liquid flow through and then clamped it back to the bar, then let a bit more flow through. Completed the bleed process and although it's not perfect, it does work and the lever returns all the way.

    Need to test it a bit before setting off to do the Badger Divide on Wed.

  • Just picked up some Magura brakes off of on here and I need to buy hoses for them.
    I don't want to pay £70 for Magura hoses particularly, they're £34 each or something and nothing special from what I can see.
    Can I just buy these fittings from Hope and use their hose?

  • lololololol

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Anyone know anything about disc brakes?

Posted by Avatar for Sanddancer @Sanddancer

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