Spongy lines? bleeding brakes.

I have the front end off a 83 xj750 on my 650. I rebuilt the calipers and cleaned out the lines and bought a new dual master cyclinder from partsnmore. I put it all together and bled the brakes. the lever was still very spongy (as in, I could pull it to the bar, but the bike would stop). I figured I didn't bleed them right so I took it to a shop where my buddy works and had him do it. Same thing. Still just as spongy. I though maybe partsnmore sent me the wrong master cylinder so I took it apart and measured. The piston is 16mm like I ordered. When I sqeeze the lever I can see the lines move just a little bit as they build pressure. It's not as if I can see them swell but they almost like twitch. Is it possible that the lines are so old and bad that they are swelling and that is what is causing my spongyness? Or after bleeding it three times (once at a shop with the right equipment and at least twice with my mitivac) and using about 85oz of brake fluid, could there still be air in the lines. I've tried everything I could think of. even tapping on the joints with a hammer. How much air would cause this? I'm probably going to order stainless lines either way but I just wanted these on until I get the SS lines. Thanks in advance for any help.

 

Soft, old rubber will expand, simple fact. Get them replaced w/S.S. and make sure you siphon fresh fluid out of the bleeders, keeping the master cylinder topped off while your at it.

 

I'm about 90% it's the lines. Just ordered new ones from http://www.cyclebrakes.com They should be here next week. I'll post when I get them on. Thanks

 

yep, I got rid of the sponginess by replacing my two piece lines with a single stainless line and new banjo bolts.

Worked like a charm.

 

Almost forgot about this post. I got the lines from cyclebrakes. They are just what I needed. I decided to go with two lines all the way to the master as suggested by Melissa over the phone. Top notch quality and make the bike look and stop great. I'll be order from them for my other bikes.