I've replaced my old brake pads in SRAM Guide R brake set, and I've noticed that the old pads were sitting much closer to the rotor than the new ones (I've also definitely used all of the old pads). As a result, now the rotor is being squeezed by the new installed pads.

How can I adjust the pads to the desired (more space between them) position? Could I just release some brake fluid (while bleeding) to decrease the pressure in the system and hope that it would pull the pistons back? Or is it more likely that my system is contaminated and I should clean the pistons?

Looks like this:



1 Answer 1


You did push the pistons full back into the calipers before installing the new pads, right? That should provide enough room for the new pads.

There seems to be a widespread misunderstanding about how hydraulic brakes work which leads people to think that removing some fluid will make more space for pads or set the pads further apart.

You cannot reduce the amount of fluid in hydraulic brakes, because it is variable and has a reservoir in the lever units to draw from. Fluid is drawn in to compensate for brake pad wear and gradual advancement of the caliper pistons. Also, fluid can move back and forth as the temperature changes and the fluid expands or contracts.

The way this works is when the levers are at their 'at rest' position the reservoir is connected to the lever cylinders by a small hole which allows fluid to move in or out. The first part of the travel of the lever piston in the cylinder cuts off that hole to the reservoir and seals the system. Then, as the lever piston applies pressure the caliper pistons are pushed out to apply the pads against the rotor.

The small hole connecting the lever cylinder to the reservoir also allows you to push the caliper pistons back in to the calipers when replacing the pads.

  • The problem is that I can't push the pistons all the way back, they won't move. As a matter of fact, I probably have made things worse by pressing the lever while I had the pads off, which caused one piston to fall out and some fluid to drip. I managed to clean it and put the piston back in, but now it's stuck (all pistons are) and they're not moving either way when I pull on the lever. What would be the proper way to go about it in this case?
    – arunasm
    Commented Apr 18, 2020 at 16:08
  • 1
    @arunasm you probably have air bubbles in the system which is compressing when you pull the lever, and is the reason why the pistons do not move. I'm not sure what the exact proper procedure is here is but it's definitely going to involve a proper bleed process. Search this site for questions on what to do when you pop a piston out, if you don't find a good answer post a new question. Commented Apr 18, 2020 at 16:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.