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I recently changed the brake pads on my Shimano 105 (ST-R7020), and when pushing the pistons back, I felt a "pop", and the pistons moved back with no resistance at all.

After using the bike for a couple of days, the brake now does not work anymore. It has become very "spongy" and does not maintain the pressure. I can pump it again, and then it keeps pressure for a while, but then soon loses pressure.

I have tried bleeding it again, without success. I fear that something is broken in the brake lever - something that would normally prevent the spring between the brake pads from pushing the oil back in the reservoir.

Since a new brake lever is expensive, I was hoping someone would know how to fix it? Or know where to get spare parts for the brake lever, instead of having to buy a completely new.

  • Brake pistons are brittle, what did you push them back with, could they be cracked? Are there any signs of oil leaking out either at the lever or the caliper end, or along the hose? If the brake has become spongey there must be air getting in, so you need to find out where the leak is located – Swifty Feb 5 at 11:02
  • Something obviously broke, but, when the brake lever is in its 'resting' position, there is actually nothing preventing fluid moving from the caliper to the reservoir. The initial movement of the brake lever piston is what cuts off the reservoir from the rest of the system. The resistance is just due to having to force fluid through narrow orifices. – Argenti Apparatus Feb 5 at 12:41
  • The brake pad spring is just there to stop the pads rattling around in the caliper, it is not strong enough to push the pistons through their seals even. I think if you check the pad position when the brakes are 'spongy' you will see they have not been moved away from the rotor. – Argenti Apparatus Feb 5 at 17:16
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I resolved the problem by changing the caliper. Now everything is working fine. Thanks for all the help, and details on how a brake system works.

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    Glad you solved the issue and that a new shifter unit was not required, Can you take the caliper apart and find out what failed? – Argenti Apparatus Feb 10 at 12:42
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    I took the caliper apart, but was not able to see any apparent causes for the error. – Bjm Feb 19 at 11:02

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