Troubleshooting Hydraulic Disc Brakes I replaced the fluid in my hydraulic disc brakes as they would not work within the first 10 minutes of cycling and would gradually sharpen up. I suspect they had air in the system.

They were sharp for about 2 weeks after replacing the fluid, but now my front brake has almost no stopping force.

How do I determine the cause of the issue?


Should I replace the fluid again?
Could there be a leak in the system?
Do I need to replace the tubing/screws?


Thanks
Tracking down issues with brakes can be difficult.  If the brakes are spongy feeling initialy and pumping them firms them up then you probably have air in the system. if that's the case then it will be a bad bleed or the seals or possibly the brake hose but working out which is often down to luck. If they just have no power it could be contaminated pads.

If it was me then I'd do the following, give the system are realy good clean and finish off with disc brake cleaner if you have some.  Next I'd re-bleed the brakes (having first pushed the pistons right back) and then fit new pads.  Use the brake somewhere safe and then inspect everything to see if you can spot any leaks at the levers, hoses or calipers, take the pads back out and check for contamination with brake fluid.

If you do have a leak then you'll need to replace the seals and/or hoses that have failed - this can be tricky if it the caliper seals that have gone. Getting hold of spares can also be an issue.

It may be easier and cheaper in the long run to replace the brakes. Shimano Deore are relatively cheap and very efective.