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Dude where's my bubble

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
Where's my bubble dude?

I'm trying to bleed my Shimano XT M775 brakes and am struggling. I typically do the motorcycle bleed, top down, but I tried the bottom up method today. My front was done in a single shot and it's beautiful. My rear brake is continuously struggling with a bubble somewhere in the brake. I tried bottom up, I tried top down, I've checked the fittings, I've tapped the caliper and MC. Every time I seal the brake back up, I get squishiness. What am I doing wrong? Where could this bubble be? How can I get it out?

FWIW, before I started messing with it, the brake was OK but a little soft. Now it clearly has a bubble in the line.
 

Westy

the teste
Nov 22, 2002
54,241
20,022
Sleazattle
Are you bleeding via pressure or vacuum?

If you can pull on a syringe and create a vacuum any bubbles will get bigger and move faster.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
Are you bleeding via pressure or vacuum?

If you can pull on a syringe and create a vacuum any bubbles will get bigger and move faster.
okay this might be it- when I pulled I was getting some gnarly bubbles- I thought it might be a leak in the system that I was using. When I pushed everything was looking clean.


what kind of beer did you have while working on your bike?
None, I was in an HR session at work about personality "color"- so I fucked right off and installed a new axle and cassette on my onyx hub then bled my brakes.
 

Nick

My name is Nick
Sep 21, 2001
23,928
14,450
where the trails are
Don't trust suction unless you're positive you have an airtight syringe fitting.

How many bends do you have in your rear brake line? Never hurts to remove the caliper and let it hang so air bubbles have a straight path to escape out of the top.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
Not many? It's a hybrid bike- it's pretty straightforward. I can still try though. I figured air was getting in through the bleed screw. Pinkbike recommends the moto bleed, which I tried but maybe not enough? I'm just so confused, this is like a HUGE bubble, not a "hypersensitive bro on the internet" bubble. A few pumps at the lever and it seems OK, again suggesting air in the lines.