Brake bleeding help

[mike-evans]

right on my 01 yz 250 i bled my rear brake earlier, stinking fluid came out, nice new clean fluid in there, feels ok :) . Fitted brand new pads on the front, but disc needs replacing, it has worn a groove in the centre where the pads contact, so i attempted the front, and couldnt get it to feel solid, stil a litle spongey :( ...air in system? I noticed when i had a clear pipe on the bleed nipple going into a jar of fluid, when i pump the lever, hold the lever, open nipple, close nipple, release lever then i could see the fluid going back up the pipe as if its going back into the caliper...i also noticed when i look into the master cylinder with the top off it, the hole where the fluid goes through with the litle flap type seal if i squeeze the brake hard i would get a bubble up out of that hole, does that mean i need a caliper/master cylinder seal kit? No leaks at all on caliper or master cylinder, could the spongey be due to worn disc? Any ideas?

 

[Patman]

It's easy to get air trapped in the front brake system. Best to either use a vacuum pump to bleed it or pull it off and hang it up so the bubbles havee a nice easy path out (i.e. UP). Tap the hose and other parts a little and you go along to help dislodge the bubbles as they tend to stick to the walls of the hoses. It is possible you need to rebuild / replace the master but that's sort of an on-site determination. You might not have a good seal on your bleed hose, maybe the nipple is too lose, cracked, bad thread.... Start with the easy stuff and that's doing everything possible to bleed it properly.

 

[julien_d]

Pat's got it nailed. It's a real bear to completely bleed the front brakes. Air bubbles coming out the master would indicate air in the system. Taking the whole system off and hanging it up has worked for me. You might have to bleed it from the master afterward.

 

[sharky243]

I've had to use a vacuum pump to get all the air out. If that doesn't work, you may need to rebuild the master cylinder.

 

[mike-evans]

thanks for the replies guys. Another thing i am experiencing with the front brake is, after fitting brand new pads when i pump the lever to get the pads/piston in position there is alot of rubbing between the pads and disc, as if the pads/pistons are not returning? Could the pistons be corroded/seizing? They were not extremely tight to push back in to fit new pads tho...

 

[Patman]

Get the air issue resilved first then see if that's still an issue. One thing at a time.

 

[whenfoxforks-ruled]

Did you replace the front brake rotor? If the master seal is gone, it will not push pressure to the caliper. Neither end pushes much fluid, a little unnoticeable bubble in the stock hose will cause issues. A stainless replacement will get the solid feel back, and then some! Vintage Bob