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Repeatable air in rear brake line

NPS

Cruisin' Guzzisti
GT Contributor
Joined
Dec 11, 2008
Messages
262
Location
Churchdown, Gloucester, UK
Breva 1100
I replaced the rear brake master 18 months ago. I have a recurring problem with the rear brake pedal going soft over a month. On bleeding, air always is there after about 6 pumps. Not initially. So Im thinking it is not the slave as the air would be ready to pop out on first bleed. I have no oil leaks. Im wondering if there new master could be faulty with damaged cylinder or seals.
Has anyone had something similar or have any ideas?
 
ABS? If not take caliper off & reroute to have lines go up caliper on a stool, bleed on top w/wrench between pads. Helps to tap on lines especially by elbows & joints. That way trapped air bubbles come loose & go up above where master & reservoir are located.
I use a power bleeder connected to air compressor on models w/side by side pistons cause passage holes are smaller than older Tonti models.
On your master make sure the piston comes all the way back at end of stroke, otherwise holes don't line up inside.
 
My '08 Norge does this too.

I haven't replaced anything yet, but I can't keep my rear brake working either, it goes soft and spongy after a month or so like you describe. it wasn't like this the first 2 years I owned it (I bought it used).
 
There should be a little bit of play on end of stroke with the linkage. It helps to tap on the lines and elbows when bleeding in case a bubble gets stuck.
 
I have a 2009 Norge with the dodgy soft spongy rear brake. When it gets soft and spongy I hang a dumbbell from the pedal overnight and it firms it up again. Don’t know why this works but it does for a while anyway.
 
I'm having much better luck this time around after re-bleeding my rear brake. it seems that i just needed to pull some more fluid out to get more air to come out. it's holding now so far and grabs right at the top of the pedal.
 
Fact not opinion here... Fluid life/condition likely plays in here on older machines. Air can be caused due to temperature variations and overheating the fluid. Change the fluid annually as a minimum. Most bikes we see in my shop have never been changed since new. Even with new fluid, bikes that get a lot of rear brake exercise need bled monthly in my personal use and experience.
 
That's kind of the funny thing about this, i had replaced the brake fluid myself and that is when I started having this issue.

I'm chalking it up to me probably doing it wrong the first time...
 
That's kind of the funny thing about this, i had replaced the brake fluid myself and that is when I started having this issue. I'm chalking it up to me probably doing it wrong the first time...
Possibly... and if you changed the fluid, I'll up those odds. ;)
 
The cause was overheating. I wrapped a short section of the exhast near the box with fibre glass tape. Not had a problem since. I think I have dot4 fluid. Dot5 or 5plus have higher boiling points so a further option.
 
The cause was overheating. I wrapped a short section of the exhast near the box with fibre glass tape. Not had a problem since. I think I have dot4 fluid. Dot5 or 5plus have higher boiling points so a further option.


The Brembo brake system is not compatible with DOT 5 as far as I know.
 
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