Topic: front brake caliper piston stuck?

[jaannaktin]

 

I got a new tire mounted on the front and tried to replace the wheel. The brake caliper would not allow the disk as somehow the space between the pads was too narrow. (No, I never squeezed the lever while the wheel was off.

I disassembled the front brake caliper to look for the problem. I had to take the whole assembly to the local shop to get the allen bolts out, by the way -- they were very friendly and loosened them for free.

I found the piston to be seated very firmly and could only be coaxed out by first tapping it IN with a small block of wood and a rubber mallet. Once I was sure it would move at all, I grasped the rim with a long nosed vise grip and it was a b!@$h to get out.

The inside looked smooth and clean, and the rubber o-ring seemed to be in good shape. I lubed the whole thing up, but the piston would not slide freely with the o-ring in position. It seemed to fit very nicely without the o-ring in place. I assume it is supposed to slide pretty freely so it can "retract" back into position when the brake lever is released?

I am not sure how freely the piston is supposed to move normally, and posted this as a long winded question as to what to do next?

I ordered a new o-ring, but am stumped how else to proceed. I don't want to rebuild the caliper if it won't function like that.

Thanks!

Jaan

[Jonesy]

Did you check the groove the O-ring sits in? Usually they are full of junk and corrosion. Carefully clean out the groove, taking care not to scratch the surfaces. I find a dremel tool with a tiny wire wheel works well. With everything clean and lubed with brake fluid, the piston should push into the caliper (O-ring in place) with little effort.

[TwoTired]

Something that works well for me is brake parts assembly lube.  Very slippery, keeps metals from corroding and compatible with brake fluid.  You really should be able to push the caliper piston in with your thumbs.
Cheers,

[kaceyf2]

The groove that your piston seal sits in is the culprit allright,  getting at it to clean all the #$%*e out is awkward, use a dremmal wire wheel but MAKE SURE THE WHEEL IS A BRASS ONE AND NOT, I repeat NOT stainless!!!!
The brass one will not hurt the alluminium,,,,
If you want to cut down on the crud that builds up use silicone brake fluid, benefits are great especially that it dont hurt paintwork!!!!
regards,
kaceyf2