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I'm going to be taking apart a Clarks Skeletal Hydraulic Brake system to try and identify what's wrong with it (trying to remove/unstick a piston), so I was wondering does it matter whether I just disconnect all the fluid cables to the caliper and let them drain, and then do a bleed/refill later?

Most videos I've seen of doing a brake fluid bleed, the system is usually still quite full of fluid, and I can't think of any reason why not but I thought I'd ask whether there's any problems with just emptying the system out.

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  • There should not be a problem, because hydraulic brakes have to be filled when they are first installed. The difficulty may be finding instructions on how to do the initial fill properly. – Argenti Apparatus Feb 2 '19 at 12:51
  • Just be sure to do a really thorough bleed. – Daniel R Hicks Feb 2 '19 at 13:14
  • Verify that you have the correct fluid when you refill. It may be a brand specific fluid or something generic like mineral oil. The wrong fluid can lead to problems later on. If you bought the bike used there is the possibility that the wrong fluid was used and damaged the seals preventing the piston from returning. – mikes Feb 2 '19 at 23:35
  • Yeah the bike was brand new when I bought it, and I bought some Carol DOT4 brake fluid off of Amazon to refill it with. I also bought the Clarks bleed kit so I have all the tools. – Zooka Feb 4 '19 at 13:08
  • As Argenti said though, my biggest concern was about perhaps air messing something up if I had to get access inside the brake caliper. Will have to enquire with the manufacturer if there is initial fill instructions. – Zooka Feb 4 '19 at 13:09
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I think this is mostly a problem in the bottom of the calipers where a hose becomes a reservoir filled with fluid, and perhaps that can get air in there. What I have done in situations like this is to make sure a block is in the caliper and squeeze the brakes a few times before opening the ports to bleed. My theory is that will do it's best to fill the fluid into the air pockets and get the air to come to the top. Of course, it's hard to see inside the actual line so hard to know. Bleeding from the caliper then gets the air out of the line. It's worked for me and given non-squishy levers in the past.

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