Did you ever get any resolution to this? I've posted with a reference to your post, but only one response.

I'm trying to figure out what going on with my front brake on a 2006 525 xc. I've replaced the piston in the hand brake, but I can't seem to get it to charge up. There is nothing there. Everything looks clear and the line looks good. I suspect the "Anti-foam" disc might be inhibiting flow to the cylinder, but I took it out and cleaned it. (Is there and orientation here?). Today, I'll pull the line and work my way down to the calipers. Any suggestions?

I'll start a new thread on this and see what shakes out.

 

hey i had the same issue on my 00 exc 300

it should be too different though your a more updated
i found it so much easier with 2 people

undo nipple one full turn
bleed it though till the no air in the line
tighten nipple on calliper
and pump for lever for a solid 4 to 5 mins
hold lever in and open and close nipple
continue this procedure until calliper is fully pumped up
never open the nipple without the lever pulled in or else it will suck air back in
and don't let the master cylinder empty it will draw air from the top
my front brakes are so good now i use too fingers and it ends

 

Couple of things that I've tried that have worked for me.

1. Back bleed the brakes. Get your hands on a large syringe,(can be purchased at a drug store) attach a rubber hose to the end, suck up some fresh brake fluid, attach the rubber tube to the brake nipple, open the nipple and slowly press on the syringe plunger to deliver the fluid to the brake.

Two things to note with this method, make sure you drain out some of the old fluid from the reservoir BEFORE back bleeding otherwise you will overflow the reservoir and the other is, if you have someone to help you rather then having them stand there and watch you get them to work the front brake lever this will allow the brake fluid to move past the plunger.

2. I made a small spacer that I put between the brake lever actuator screw and the reservoir plunger, most of the time the Brembo actuator screw is just a little too short to seat on the plunger which makes it feel like the brakes are not working correctly.

I had the same problems you've described, these little tricks worked for me.

 

I also had issues with a spongy brake lever. Initially, i had tried to bleed the brakes using gravity and a one-way motion pro valve which did not work that well (this method works awesome on my cars and also with the clutch on my KTM). So, then I tried what the previous poster suggested with back bleeding the brakes and it got a lot of air out of the system and was better but still not perfect. So, finally, i tried the zip-tie technique and that finally took all of the sponginess away and got all the air out of the system. Back bleeding can be a little messy so I wonder if the zip-tie technique would work by itself. The zip-tie technique is when you zip-tie the brake lever to the throttle so it's fully engaged and leave the cover to the reservoir open overnight.

 

On an older KTM we have, nothing would solve the problem (2 full rebuilds, bleeding, "zip tie" technique etc). We would get temporary relief, but problem would come back (spongy brake feel) very soon. So I bought a s/h Yamaha master cylinder. It has now been on the bike for 3 years and not once have I needed to air/bleed or rebuild the thing. Our 2016 KTM 125sx is starting to show similar symptoms so I will soon buy a Yamaha master cylinder for that one too.