RMX250 brake issues

[matrox02]

Hi Guys, I recently purchased a 1990 rmx 250 and to begin with the project I decided to rebuild the brakes as they where feeling tired and not stopping very well, so i pulled them to bits and overhauled them( rebuilt master cylinder and new caliper slide seals and new piston seals ), and bled the brakes.. over and over and over again, for what ever reason i cant seam to get the last bit of air out the lines, I first thought that i mucked something up so pulled apart and confirmed that all the seals were good so re assembled and they feel a little better, but still spongy and feel like it takes 5-6 pumps before it actually feels any good under the hand ( i dare not try it rolling yet , as i quite literally have the lever hit the bar and the wheel can still be pushed around with a bit of drag until i pump the brake a bit) I bought a vacuum bleeder and it seams like it doesn't get a steady stream of fluid so i though that the nipple may be bypassing air so replaced that and still no joy, I even tried a different master cylinder and line, only the calliper is the same and it still feels spongey, so am i right to assume that the caliper is likley harboring air in the piston valley?? Iv tried soooo many methods of bleeding it and have zero joy on the bike Im thinking i may have to bench bleed it and pull one of the pads out for further extension of the pistons to dislodge the air maybe??

so far iv tried gravity bleeding, pumping the brakes and then opening the nipple and then closing the nipple then release pump and repeat , and that vacuum pump method, also tried tapping the MC and the Caliper to dislodge air, but nothing ...

so yeah im at a loss, any tips would be good?

[eelracing]

any tips would be good?

It could be the actual lines themselves,when they degrade they get internal blockages and endlessy bleeding them gets you nowhere.
I had the same symptoms on my old Nortons rear brake and a full replacement fixed it.

[F5 Dave]

unlikely on std system but try pointing the calliper down a bit more & do some bleeds. So either pull the calliper off & get someone to hold it on another part of the disc, or just raise the rear considerably. This helps if there is a pocket above the bleed nipple in the casting, only has to be tiny, perhaps due to the stand raising the bike a bit?

Other thing is wrap a rag around the banjo bolt & open it while mate pulls brake lever, close, release. Then the top one.

[matrox02]

Ill probably pull the whole assembly off the bike when i have time and get a friend to help me with it, by the sounds of it ill have to remove the pads and pump them all the way out then force them back in to dislodge some air as some one else had mentioned to me, otherwise.. my next step is braided lines...

[pete-blen]

I just had that issue with my XT... couldn't get anything... I took the
master cylinder off lay it on the ground so it was below the caliper..
10/12 pumps/bleeds I had brakes..
Another trick I have found is if the bake line goes up higher than
the master cylinder "most do" air can sit in the line... tie it down so it's
lower than the master cylinder... any air at that point can bleed out though
the master cylinder...