c3024446
Likes Bikes and Dirt
My rear brake keeps developing a bubble in the calliper, and I don’t know what’s causing it. On the bike it looks similar to this (i.e. bleed screw facing down):
I’ve recently put a new shimano BH90 hose on the brake (brakeset is 3yo, old hose was leaking contaminating the pads, note this was not a Shimano hose). After installing the new hose, I bled the brake correctly, lever was solid. Put the bike back into the horizontal position. After a couple of hours, I go to squeeze the lever, and it’s squishy.
If I stand the bike up vertical, the lever becomes solid again. With it still vertical - I connected a bleed hose to the calliper bleed nipple, squeeze the lever, loosen nipple, a bubble comes out with some the fluid. Re bled the brake. Test lever in horizontal after waiting an hour – squishy again! The process keeps repeating! A bubble seems to form in there, then move to the bleed port with the bike vertical making the brake solid, and floats behind the pistons when horizontal.
So there is a leak in the calliper somewhere. I have ziptied the lever to pressurise the brake, ridden the bike a lot, but I can’t find the leak! It’s like it’s a one way leak where the calliper is absorbing air under vacuum or something?
How can I find the leak? – It has to be at the hose join to the calliper, at the bleed nipple, or the piston seals. It can't be at the lever end. I’m sure it isn’t the infamous leaking banjo issue since it is a brand new hose. Is a new calliper the only solution?
I’ve recently put a new shimano BH90 hose on the brake (brakeset is 3yo, old hose was leaking contaminating the pads, note this was not a Shimano hose). After installing the new hose, I bled the brake correctly, lever was solid. Put the bike back into the horizontal position. After a couple of hours, I go to squeeze the lever, and it’s squishy.
If I stand the bike up vertical, the lever becomes solid again. With it still vertical - I connected a bleed hose to the calliper bleed nipple, squeeze the lever, loosen nipple, a bubble comes out with some the fluid. Re bled the brake. Test lever in horizontal after waiting an hour – squishy again! The process keeps repeating! A bubble seems to form in there, then move to the bleed port with the bike vertical making the brake solid, and floats behind the pistons when horizontal.
So there is a leak in the calliper somewhere. I have ziptied the lever to pressurise the brake, ridden the bike a lot, but I can’t find the leak! It’s like it’s a one way leak where the calliper is absorbing air under vacuum or something?
How can I find the leak? – It has to be at the hose join to the calliper, at the bleed nipple, or the piston seals. It can't be at the lever end. I’m sure it isn’t the infamous leaking banjo issue since it is a brand new hose. Is a new calliper the only solution?
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