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Hydraulic discs, can't get stiffness.

KnobblyShinsKnobblyShins Posts: 4
edited August 2011 in MTB workshop & tech
Hi,

Got my bike (2006 trek 8000, http://www.bikepedia.com/quickbike/Bike ... &Type=bike) out after winter months in the shed, brakes (Deore XT) seized up, pushed the pistons out and back a few times to loosen them up, one piston at the front stuck and the other side popped out quite far and ended up leaking fluid, there was also some leakage from the reservoir on the handlebars. Since tried to bleed with new fluid. The new fluid has comes through but no stiffness in the brakes, and can't seem to completely get rid of air. Anyone got any idea what I've done? Are we talking a new brake?

Cheers!

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  • nicklousenicklouse Posts: 81,520 Lives Here
    you need to bleed the brakes.

    sounds like you have a pile of air in there.
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  • cooldadcooldad Posts: 32,904
    Sounds like you tried, as opposed to succeeded.
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  • Fairly sure you won't have to write the brakes off and that is a beautiful bike.

    Can you describe the procedure you used to bleed the brakes? Any guides you followed etc.

    If you squeezed the brake lever repeatedly to bleed the fluid then some air will have entered it.

    Do the bleed again. I am not an expert, but if you have the syringes attached to both ends (lever and caliper) creating a vacuum on one side should draw all the air within the system to the syringe. You can then carry on with the process.

    I found a guide for Shimano brakes and back bleeding here: http://www.krankdirtwear.com/fix-your-b ... rkshop.pdf

    Hope it helps you out.
  • Hi,

    I used the Shimano manual for these, i.e. M585, brakes. You're supposed to "Loosen bleed nipple by 1/8 turn, pour oil into reservoir tank, gently operate brake lever to help prime system with oil". I got some (well, a lot) of air out, but eventually flow stopped with still no resistance in the brakes. There's no mention of using syringes in there. For lots of air in the system/no stiffness they suggest (i) tightening the nipple, waiting and operating the lever (bubbles then surface in reservoir, apparently) (ii) changing caliper position, shaking hose. To bleed the calipers pull the lever and quickly untighten/retighten nipple several times (but I guess this assumes having successfully primed the rest of the system). Thanks for the link - perhaps the calipers are just too full of air and back bleeding or using a syringe is the way to go.
  • Have a look at the pistons/brake pads. Do they move when you pull the levers? If you have movement, but no braking then you may not have enough fluid in the system to create enough hydraulic pressure to push the brake pads inwards far enough.

    Some brake levers also seem to have a pad contact point adjustment. These are for higher end brakes though. I'm assuming this is not the case for you as you've got no resistance in the brake lever at all?
  • madmolemadmole Posts: 466
    or, air in the system throughout winter means seal have gone hard and let air in constantly

    So you get fluid out the bottom nipple (when opened) and you squeeze the lever?

    The resevoir is full?
    Marin Mount Vision 2005. Fox RL100/RP3. Hope Pro 2/Mavic XC717/DT rev. Cinders 2.1, XTR, Lots of bling

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  • mister pmister p Posts: 405
    If the piston popped out enough to leak fluid it may be that the seal has stopped doing it's job properly and is letting air in.
  • jairajjairaj Posts: 3,009
    have a look at this video, its by Shimano and is pretty much the same as the manual but in video form.

    http://www.youtube.com/watch?v=YXmWziLAlBU
  • I think some of you've voiced some of my fears there! Thanks for the video link, very helpful. No movement at all on the pistons I think. I'm going to assume I just have lost so much fluid I have to start from scratch (as in the video) as though I've just installed the brake, and go from there, once my syringe arrives.
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