• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

Caliper Piston stuck open

Whats_up_DOHC

CB750 Member
Messages
10
Reaction score
0
Points
1
Location
Canada
I have a 1980 cb750f.

Today I checked one of my 2 front calipers to see if the pads where worn out, turned out they're in pretty good shape.

The thing is, I depressed the brake lever several times ( I guess I wanted to see how it worked...) while the pads were out, so the piston got stuck in the open position ! Moreover, the piston is almost out of its housing, I even did see a bit of fluid coming out of the housing.

I tried to gently tap on it with a piece of wood, it did nothing.

I don't know what to do, if you guys have a clue to what I should do, I would be very happy!

Thanks folks !
 
Loosen the bleed screw and push the piston back in the housing. You need to push as straight as you can, not pry on one edge such as with a screwdriver because the piston could get in a bind while starting it in the housing.

Easiest way will likely be to take the caliper off and push it in with a C-clamp or maybe a woodworking type clamp if you have one deep enough. Even a vise if you have one that will open far enough. Just be sure to protect the surface of the caliper so you don't scratch it. You can put the pad or a piece of wood over the piston to keep even pressure around the OD of the piston.
 
Ok that makes sense, thanks for the info !

I still have one question : If I disconnect the caliper hose to take the caliper off, what will prevent the fluid to spill all over the place? Is there some way to prevent this?

Thanks again !
 
When you disconnect the hose from the caliper fluid will come out... not really fast, but it will come out. Squeeze a rag over the sides of the banjo fitting and you'll minimize the issue... just don't let it get on your painted surfaces. Keeping the hose as high as you can will help a bit too.

Your bigger chabce of significant fluid loss could be from the caliper if you've pumped the piston out enough that it's leaking. If it falls out, you'll have a bigger gush of fluid from the housing... keep the piston side upward in case that might happen.

You might get by without disconnecting the hose at all if you have any free play and will be using a c-clamp to push the piston in. That would also be the best to prevent the need to bleed the brakes. If you want to try that, be sure you haven't emptied the master cylinder and that there's sufficient fluid it it to not allow air to get into the system. If you don't end up with a nearly empty caliper housing, you can hopefully just push the piston back in and the fluid will come out the bleed screw... into a container you use to catch the fluid.

You'll want to at least go through the motions of bleeding the system anyway once you get it back together, but there may not be any air in the system if you're real lucky... you'll know quickly if you need to do some bleeding because the lever will have no resistance, be spongy,or requiring "pumping" to get brakes.
 
Back
Top