Soft brakes

I just replaced my master cylinder on my XJ and I still have a soft brake lever. I replaced it because the old one had leaky cap, piston seal was leaking (did the fountain geyser thing) and the switch was going bad. I bled the brakes and got a lot of air out of the lines, but no matter how much I bled them, the lever wasn't getting firm. Occasionally it would get really firm, then I'd let it sit and it would get soft again. One thing I did notice, was that if I let it sit for a bit then cracked open the caliper drain screw, a nice big bubble would come out of line.

Could it be the piston seal, or am I going in the wrong direction with this? If so, would a caliper rebuild kit solve my problem? I'm kind of upset that the new master cylinder didn't completely fix my front brakes, but at the same time, the bike really needed that master cylinder.

 

Is it a NEW master cylinder, or a "new-used" one from eBay or ?

It could certainly be an issue in the caliper, those seals were supposed to last for TWO years.

Either way, if you're getting bubbles, you still have air in the system. Did you replace the original lines as well? (Equally important; they had a four-year suggested life span.)

 

It's a brand spanking new master cylinder and the lines are were replaced since I bought the bike (Dec 2010). The reason I'm suspecting the seals on the pistons more than anything, is that if I pump the brakes, then crack it open, a nice big bubble is sitting right there.

 

Good deal. Sounds like a case of "weakest link" syndrome; if the calipers are the only thing you haven't rebuilt yet...