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Hydraulic brake power loss

pangolinpangolin Posts: 4,518
edited October 2018 in The workshop
Lost all power to my front brake the other morning, as soon as I set off and went down a hill. It came back after a little bit of squeezing the lever a few times, bumping around on the road etc. I remembered that since I'd last ridden the bike I had taken it in the car so it had been on its side, and I figured an air bubble had moved from the reservoir into the hose. Problem solved anyway.

Then yesterday I lost power again, over a week since it last happened and the bike hadn't been on it's side. Power came back again shortly afterwards.

Was my original diagnosis likely correct? Do I need to add some more oil? Do a full bleed? At work the bike is stored on its back wheel, front wheel in the air, on one of those hanging racks. But the reservoir is still the highest point in that situation.

They're 105 hydraulic road brakes.
Genesis Croix de Fer
Cube Attain

Posts

  • veronese68veronese68 Posts: 25,293 Lives Here
    When you are losing power how does the lever feel? If you have excessive movement and it feels squishy but you can pump it up by pulling it repeatedly it's a bit of air in the system and a bleed should fix it.
    If the lever still feels as firm as it does normally it's not air, but more likely contaminated or glazed pads.
  • KillerclownKillerclown Posts: 110
    edited October 2018
    pangolin wrote:
    Lost all power to my front brake the other morning, as soon as I set off and went down a hill. It came back after a little bit of squeezing the lever a few times, bumping around on the road etc. I remembered that since I'd last ridden the bike I had taken it in the car so it had been on its side, and I figured an air bubble had moved from the reservoir into the hose. Problem solved anyway.

    Then yesterday I lost power again, over a week since it last happened and the bike hadn't been on it's side. Power came back again shortly afterwards.

    Was my original diagnosis likely correct? Do I need to add some more oil? Do a full bleed? At work the bike is stored on its back wheel, front wheel in the air, on one of those hanging racks. But the reservoir is still the highest point in that situation.

    They're 105 hydraulic road brakes.
    It certainly can’t hurt to do a bleed. Certain brake fluids are more hygroscopic than others ( which is another different issue ) so the oil can need replacing if you ride a lot in damp rubbish conditions.
  • pangolinpangolin Posts: 4,518
    Veronese68 wrote:
    When you are losing power how does the lever feel? If you have excessive movement and it feels squishy but you can pump it up by pulling it repeatedly it's a bit of air in the system and a bleed should fix it.
    If the lever still feels as firm as it does normally it's not air, but more likely contaminated or glazed pads.

    It's very squishy. Almost like it's not connected to anything, as it the cable had snapped on a cable brake.
    Genesis Croix de Fer
    Cube Attain
  • pangolin wrote:
    Veronese68 wrote:
    When you are losing power how does the lever feel? If you have excessive movement and it feels squishy but you can pump it up by pulling it repeatedly it's a bit of air in the system and a bleed should fix it.
    If the lever still feels as firm as it does normally it's not air, but more likely contaminated or glazed pads.

    It's very squishy. Almost like it's not connected to anything, as it the cable had snapped on a cable brake.

    That sounds like air in the system, or a jamming valve, so the lever is moving without letting the fluid down.
  • veronese68veronese68 Posts: 25,293 Lives Here
    It certainly can’t hurt to do a bleed. Certain brake fluids are more hygroscopic than others ( which is another different issue ) so the oil can need replacing if you ride a lot in damp rubbish conditions.
    Shimano fluid is LHM which is not hygroscopic, DOT fluid used in SRAM systems is hygroscopic.
    Does sound like it needs a bleed, but it's not moisture related.
  • Veronese68 wrote:
    It certainly can’t hurt to do a bleed. Certain brake fluids are more hygroscopic than others ( which is another different issue ) so the oil can need replacing if you ride a lot in damp rubbish conditions.
    Shimano fluid is LHM which is not hygroscopic, DOT fluid used in SRAM systems is hygroscopic.
    Does sound like it needs a bleed, but it's not moisture related.

    I couldn’t remember off the top of my head, which fluid was in which system, but you’re correct the LHM isn’t hygroscopic.
  • How are the wheel bearings? If there's any play/wear movement then the pads can/will be pushed back from the disc making lots of pumping needed to squeeze them against the disc fully, will also make the lever feel soft spongy too.
  • pangolinpangolin Posts: 4,518
    cambiker71 wrote:
    How are the wheel bearings? If there's any play/wear movement then the pads can/will be pushed back from the disc making lots of pumping needed to squeeze them against the disc fully, will also make the lever feel soft spongy too.

    Hmm I'll check. I think they're fine but I'll have a good look. It's only done ~700 miles.

    Assuming they're OK I'll try bleeding. Thanks all.
    Genesis Croix de Fer
    Cube Attain
  • cambiker71 wrote:
    How are the wheel bearings? If there's any play/wear movement then the pads can/will be pushed back from the disc making lots of pumping needed to squeeze them against the disc fully, will also make the lever feel soft spongy too.

    Which is true of car wheel bearings as well. I’ve had a brake pedal go to the floor on a car because of a failed wheel bearing.
  • veronese68veronese68 Posts: 25,293 Lives Here
    cambiker71 wrote:
    How are the wheel bearings? If there's any play/wear movement then the pads can/will be pushed back from the disc making lots of pumping needed to squeeze them against the disc fully, will also make the lever feel soft spongy too.
    Which is true of car wheel bearings as well. I’ve had a brake pedal go to the floor on a car because of a failed wheel bearing.
    Once drove a supercharged MGB back from Birmingham that did that. The speedo didn't work and at motorway speeds it took two full length pushes of the pedal to get the brakes to work. Brakes on those aren't great when they work properly, I later worked out how fast I'd been going by revs and gear ratios. Never drove that car again. :shock:
  • Veronese68 wrote:
    cambiker71 wrote:
    How are the wheel bearings? If there's any play/wear movement then the pads can/will be pushed back from the disc making lots of pumping needed to squeeze them against the disc fully, will also make the lever feel soft spongy too.
    Which is true of car wheel bearings as well. I’ve had a brake pedal go to the floor on a car because of a failed wheel bearing.
    Once drove a supercharged MGB back from Birmingham that did that. The speedo didn't work and at motorway speeds it took two full length pushes of the pedal to get the brakes to work. Brakes on those aren't great when they work properly, I later worked out how fast I'd been going by revs and gear ratios. Never drove that car again. :shock:

    Scary stuff! i'm a garage foreman, seen it a few times, always makes for an interesting road test :roll:
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