Topic: Where is the air in my rear caliper coming from?

[endobendo]

Hey everybody, I have a 76 CB750F.  I just love the rear brake, but sometimes it tries to make me rearend the car in front of me.  I replaced the line with a stainless one and have new banjo bolts and copper washers.  I also never loose any fluid; there are no visible leaks.  The brake can be tight as ever for a week or more, but other times it is full of air.  I can bleed it till it is fine, then a day later it has just as much air in the line.  Where is the air coming from?  I got a new kit for the master cylinder, but the problem seemed to go away when the parts showed up.  Now it keeps coming back.

I'd appreciate any ideas.

[Alan F.]

I think I'd check out that o-ring on the caliper piston, air could be coming in around it if it's old and worn, failing that..how badly pitted is the piston?  Also be sure to use NEW brake fluid from a previously unopened container (it's said that brake fluid will absorb moisture and become less effective after sitting a while)

[bike54]

hi all
little tip for saving a opened can of brake fluid if its in a plastic bottle fit a peice of cling film over the top before refitting the top and squeze the bottle to get the air out so it looks full then fit the screw top

merv   

[Bodi]

I've had fricking nightmares about bleeding those brakes, it's very hard to get all the air out because the brake line is nearly horizontal and gravity doesn' help work the bubbles to either end. If you can dismount the caliper or the master cylinder and hang it so the line goes up towards one end along its entire length, then let it sit like that for a few hours... the bubbles should all go up to the top and then you can bleed it again using the bleed screw at the caliper or pressing the caliper piston in to force the air out the caliper bypass hole.