Front brake piston not retracting??

[antwan]

Hey y'all,

my front brake seized up on me a while ago and when i went to take it apart i realized that the bleeder screw was broken off in the caliper, I just bought the bike not to long ago and didn't realize when i bought it. On top of that the guy had tried to get it out with a screw extractor and had broken that off inside the bleeder screw so there was no chance of getting that thing out. So i bought a new caliper and a rebuild kit from eBay.

After installing it and bleeding the brake line, i noticed that the front wheel was locked up again. I guess the piston was retracting inside the caliper, so I figured I should rebuild the master cylinder, which I did.

Just finished putting it all back together and bleeding the line again.... same problem, brakes aren't retracting. When pulling the brake lever it is super stiff about half way through and almost impossible to bottom out.

Any thoughts??

 

[nrcb125]

Sounds like something on the caliper pistons are causing them to stick. Here's a thorough guide for cleaning/repairing a Ninja 250 brake caliper. It should be more or less the same for any brake caliper. Hope this helps!

http://faq.ninja250.org/wiki/Brake_caliper_rebuild

 

[Djfob]

Do the pads move smoothly inside the caliper?

 

[antwan]

Thanks nrcb but the caliper and brake pads are all brand new, no need for cleaning.

And yes Djfob, the brake pad slid right in the caliper no problem.

 

[nrcb125]

Hmmm. You could try putting the master cylinder onto another caliper which you know works and see if the same thing happens with another caliper. And pair the caliper to a master cylinder you know for sure is working. You'd be able to tell which part was the issue then. Is the brake line new and unclogged as well?

 

[ILoveThumpers]

Likely problems:

1) return port in brake master is blocked. I know you just rebuilt it, but did you clean all the passages?
2) piston seal is installed backwards. They aren't perfectly square. When installed, the low edge should be OUT. (High edge towards the back of the piston.
3) there is a rubber collar on one of the pins that connect the caliper to the mounting bracket. If it's swolen or pinched, the caliper and bracket can't slide freely.

When the brake sticks, what happens when you break the bleeder open? Do you get a jet of fluid out or just a drip? (Or none)

-Deek