Hydraulic disc brake questions
Many bleeding procedures say to discard old fluid if its contaminated or discoloured. How can I drain the system before starting a bleed? I'd like to know 100% of the fluid in the system is good. Does this just involve pushing a small amount of fluid through in to an empty syringe?
Also, I like to clean up the pistons at the caliper. Many videos just force the cylinder out, clean it with DOT fluid (SRAM system) and then push it back in, all while saying "dont push it too far, you dont want the piston to come put of the seal"...but how do I know how far is too far?
Also, I like to clean up the pistons at the caliper. Many videos just force the cylinder out, clean it with DOT fluid (SRAM system) and then push it back in, all while saying "dont push it too far, you dont want the piston to come put of the seal"...but how do I know how far is too far?
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If your brakes are working OK do nothing.0
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They arent0
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Don’t empty the fluid first, just push new fluid through until what comes out is clean. You are more likely to get air in the system if you attempt to drain and refill.
Only allow the pistons to come out a tiny bit more than usual to clean if you must, you know it’s too far when the piston pops out and you get brake fluid everywhere.0 -
You might be better in the mountain bike section, they've been dealing with this stuff for years!
I'd suggest draining most of the fluid is probably good enough.. as for the bleeding my experience is that patience is key, put a funnel/syringe full of oil at the top of the system, wait... Jiggle the lever a bit, wait some more... Tap the hose... Move the bike into a different position, wait some more, jiggle some more.
Basically crack open a beer and let gravity do the work.
I tried mucking about with syringes at both ends and had a worse result with much more faff.0 -
Veronese68 wrote:Don’t empty the fluid first, just push new fluid through until what comes out is clean. You are more likely to get air in the system if you attempt to drain and refill.
Only allow the pistons to come out a tiny bit more than usual to clean if you must, you know it’s too far when the piston pops out and you get brake fluid everywhere.
This is what I am worried about, you know it's too far when...you've gone too far :P
Regarding the just push new fluid comment; don't you push the fluid from syringe to syringe while bleeding, so the old fluid will get pushed out but then back in. I guess we're probably talking pretty small quantities of 'old' fluid being pushed back but still, it'd be nice to avoid any if possible.0 -
Yes, I know it’s a bit daft. Unfortunately you can only find out the hard way.
Push more fluid through before you go back the other way to try to avoid putting old fluid back. If necessary remove the syringe and ditch the old fluid replacing with new. Making sure you don’t get any air into the system when you do so. Can’t remember quite how I did it but I have managed it. Being creative with the angle the bike was at helped.0 -
So had a go at the brakes yesterday. The fluid was heavily discolored and had bits in so have pushing through from the caliper to the lever I disconnected the lever syringe and refilled with fresh fluid.
However, when rebleeding the system it was dragging air in/leaking through the shifter hood. Dismantling the shifter hood revealed the bladder wasn't seated properly so put that back in correctly but it still didn't work. I don't know if this was the cause of the bad braking or happened while I was bleeding it. Either way, have ordered a new reservoir/bladder/backing plate kit so fingers crossed that'll fix the issue.0 -
