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Shimano BR RS505 Bleed

markybainsmarkybains Posts: 37
edited August 2017 in Workshop
I have recently replaced the pads on the front calliper of the BR-RS505 set and this improved the braking significantly.

I checked the back and the pads had plenty of life in them so I refitted them. I concluded that the rear calliper needed bleeding and I have tried both ways i.e. (i) using a syringe and pushing fluid up so that it becomes collected in the Shimano oil funnel and (ii) filling the funnel and letting the fluid pass from the funnel to the calliper and out into a bag which is wrapped on a tube which is attached to the bleed nipple. Neither method gives me a feel quite like the front though and that is justy from a pulling on the lever whilst idle and not from a braking power point of view.



Does anyone have any tips? Whilst bleeding should I pull the lever (with a block in place etc)

Posts

  • buckmulliganbuckmulligan Posts: 1,031
    I have a bit of recent experience with Shimano hydraulic brakes, having cracked a piston in my BR-RS785 caliper 5 days before a big race and a mad-panic to switch it out.

    In my experience, the first thing to check is if both pistons are moving equally; "dominant pistons" are very common on Shimano setups and if one is stuck or more reluctant to move then you'll get more lever travel and find it difficult to set up properly. Secondly, you can try removing the wheel and giving one or two squeezes on the lever to advance the pads a tiny bit.

    If neither of these work, you can try bleeding again; I usually inject fluid from the caliper first, tapping the caliper and hose a lot to encourage any bubbles up to the lever/funnel. I'm never quite sure what the volume of one of these brake systems is, but for a rear brake with the longer hose run, I reckon it could be up to 50ml? Once you're convinced that you've filled the system and with a good amount of mineral oil in the funnel, open and close the bleed nipple a couple of times and then let the fluid flow back down the system, from the funnel and out through the caliper; again, tap the caliper to ensure any bubbles in there work their way out.

    That has been my method and its worked fine for me several times over the last few weeks! I suspect your issues aren't to do with bleeding though, but probably to do with the pistons; have a Google for Shimano sticky/dominant pistons.
  • markybainsmarkybains Posts: 37
    Thanks for considering my problem. When you say open and close the valve and let the fluid flow back down are you recommending that the lever is also pumped at this point?!
  • The RookieThe Rookie Posts: 27,756
    How did you conclude that the rear needed bleeding? I see many people come to that conclusion when in actually fact it's clear that bleeding is certainly not needed, so what was happening that made you come to that conclusion?
  • kajjalkajjal Posts: 3,380
    A lack of braking power can be contaminated pads or rotors. Bleeding is usually when too much air gets in the system.

    Also the front brake has more braking force in general compared to the rear but they should feel / sound similar.
  • buckmulliganbuckmulligan Posts: 1,031
    markybains wrote:
    Thanks for considering my problem. When you say open and close the valve and let the fluid flow back down are you recommending that the lever is also pumped at this point?!

    No, there's no need to pump the brake lever then; the fluid should flow from the funnel to the caliper very readily just from gravity.

    After you do this step, close the nipple, remove the funnel and replace the sealing screw in the lever, THEN you can pump the lever to test the lever feel; with the bleeding block in the caliper it should feel almost rock solid.

    However, as others have said, I suspect it's not a bleeding issue per se; have you checked if both pistons are moving equally?
  • The RookieThe Rookie Posts: 27,756
    Kajjal wrote:
    Also the front brake has more braking force in general compared to the rear but they should feel / sound similar.
    Simply NO.
    The brakes develop the same force (unless the disc is smaller) its the available traction at the wheel that is different.
  • kajjalkajjal Posts: 3,380
    The Rookie wrote:
    Kajjal wrote:
    Also the front brake has more braking force in general compared to the rear but they should feel / sound similar.
    Simply NO.
    The brakes develop the same force (unless the disc is smaller) its the available traction at the wheel that is different.

    Obviously :roll:
  • pilot_petepilot_pete Posts: 2,120
    Hi Marky

    I am not familiar with the RS505 specifically, but have fitted and bled my RS785 set up a few times. So, things to check;

    1. Ensure the rear pads aren't contaminated and the rotor is clean.
    2. Download the Shimano dealer manual for your brake set up, which describes all the steps for correct set up.
    3. I have found that setting the bike in the stand tilted so that there is a rise from caliper to brake lever helps the air to travel up to the lever/ funnel. I don't just mean put the bike in the stand the correct way up, I mean tilt the rear end down further so that the brake hose from caliper along the rear stay has an uphill slope. This should mean the hose has an uphill slope all the way to the lever.
    4. Bleed following the instructions in the DM.
    5. Does the RS505 lever have adjustments for reach and free stroke like the RS785? If so, these could be causing your feel differences between front and rear brakes. Once I had bleed my brakes the reach needed adjusting on each lever to ensure the bar to lever distance was suitable for my hand size. Once this was done, each lever travelled a different amount before the brakes 'bit'. This necessitated free stroke adjustment of each lever so that the biting point was matched between front and rear brakes. Think of this adjustment as how much lever you pull before the brake is applied. You can move this point closer or further from the bars using the free stroke adjuster. I like 1/2" or so of lever movement before the brakes come on at all.
    6. If you still have a spongy feel I suspect there is still a little air in the system. You can follow other tips like tapping the caliper and pumping the lever a bit to expel that air. Even if, as others have alluded to, your initial issue was not a bleeding issue it may well be now that you have opened up the system.

    Good luck.

    PP
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