Brake piston not releasing?

[Red23]

Hey all

I just bought myself a 98 cb250 nighthawk, and when moving the bike I notice that the brakes aren't releasing on the front. Is this because the bike isn't running (flat battery so haven't had a chance to test that theory yet) or do the brakes need bleeding/backing off?

Cheers

Glenn

 

[Rich Ard]

Could be that the return valve on your master cylinder is clogged, or the piston is seized... Take it apart and find out!

 

[xb33bsa]

the square cross section sealing ring in the caliper is what returns the piston ,of course as said if the return hole is plugged that can be the issue
if you remove the res. cap and pry the caliper piston back into the caliper and see fluid returning then it is the piston seal all gunked up
you will need to take apart, clean everything and or replace seal ring

 

[titan5699]

Depending how old the fluid is, chances are you could use a fluid change.

Also make sure nothing is binding. I re-did my front brakes, new lines, cleaned caliper and new fluid but it still wouldn't release like it should. I took it apart and realized the new pad was slightly too big. The body of the pad, the plate behind the braking material, was rubbing on the caliper body, causing it to stick. A quick light sanding of the plate and the caliper body and all is well! Don't forget about the small less likely things, they always seem to pop up when you aren't thinking about them..

 

[Red23]

thanks for the replies.

I bled the system and put new fluid in and its still the same. I managed to fight the caliper off the disc and I can apply but not release even with screwdriver assistance.

I just cannot figure out how to pull it apart without draining all the fluid, and getting it in a vice. You guys familiar with disc brake front ends on the cb250? Is there a trick to it or should I just muscle my way in?

I am guessing it needs new ring seals considering I can apply but not release the brakes. I'll look into second hand calipers as well.

What is the likelyhood that the issue is in the master cylinder or the brake hose? I don't want to focus on the wrong component here.

Cheers

Glenn

 

[Rich Ard]

The likelihood is pretty good that it's the MC, which is why I suggested it :

Take the whole system apart and clean everything - it's your brakes!

 

[rockcitycafe]

to get it out, take the caliper off and keep pumping the master cylinder until the piston comes all the way out, then drain the fluid, rebuild the system

 

[titan5699]

to get it out, take the caliper off and keep pumping the master cylinder until the piston comes all the way out, then drain the fluid, rebuild the system

Agreed. That way is absolutely the easiest way to free out a stuck piston. And I would definitely not force in the piston, if that's what you were talkig about. It can damage the caliper and piston. Obviously something is not right. I would remove the piston and clean out the caliper. Lightly sand the caliper body, piston, brake pad body, any moving parts to make sure there are no hang ups. And yea, it's worth replacing the caliper seal.

Also, if everything looks fine, check the brake lines themselves. It is possible that the lines got bent and the inner steal lining got creased. It might look fine on the outside but if the inside is pinched the fluid won't be able to return. I've seen this same problem before on cars, since they basically are the same kind of hydraulic type of braking system it could have happened to one of your lines.

 

[xb33bsa]

heating up the caliper will also help free the piston ...heat gun, or a propane torch,use them carefully and get that sucker hot 250 degrees or so will really make a diff