I cannot reset my caliper pistons. What now?
resetting position of brake caliper pistons with plastic tyre lever

 

If you're having difficulty resetting the position of your caliper pistons it is probably because your brake has been filled with too much brake fluid.

The brake system can become over-filled if a brake bleed is performed without resetting the pistons. The most obvious example of this is when a bleed is carried out with part worn brake pads in situ.

Shortcuts can be taken when it comes to brake bleeding. Not removing the wheel and brake pads prior to carrying out the work is one such shortcut. It only becomes a problem when fitting new brake pads and you are unable to create enough space between the pistons to accommodate the new pads.

 

Here's how to fix it.

The problem is easily fixed by removing the excess brake fluid from the brake system.

 

Always remove excess brake fluid from the highest point. If your bike is the correct way up this will be your brake lever's bleed port or reservoir top cap. Removing the caliper bleed port screw will result in air entering the system.

 

1. Remove the brake lever bleed port screw or reservoir top cap and rubber diaphragm.

 

Shimano Deore brake lever bleed port and o-ring removal

 

2. Now try to push back the caliper pistons with your flat blade screwdriver if your pads are in place or, if your pads have been removed, use a plastic tyre lever.

3. Be sure to catch the excess brake fluid with some paper towel. Then refit the master cylinder bleed port screw or rubber diaphragm and reservoir top cap.

 

Shimano Deore brake lever bleed port and o-ring installation

 

4. Wipe away any brake fluid from your lever assembly with a wet rag.

 

Shimano Deore brake caliper without pads in - reset pistons

 

Now you've successfully reset the position of the caliper pistons you can go ahead and insert your new brake pads or bleed block.


Alex Mansell Epic Bleed Solutions

Alex Mansell, Head honcho
Shares tips and advice on the dark-art of brake-bleeding. Rides bikes when time permits.
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  • Nov 04, 2019
  • Category: FAQ
  • Comments: 0
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