Front brakes won't bleed

[Dell'Orto]

So finally got around to bleeding up my brakes today. Rears came up mint, but when I started on the fronts, they just don't want to play ball!
With a mityvac, I can pull fluid through to the caliper, but the pedal will not move any fluid at all. I didn't bench bleed the master cylinder when I rebuilt it, but I did disconnect the front pipe from the m/c and pulled fluid through with the vacuum bleeder.
Oddly, the pedal will go to the floor with either rear bleed nipple open, but as soon as they're closed the pedal goes hard again. Even with the front brake pipe undone from the m/c the pedal stays rock hard. Help?!?
Running all AE86 brake system

[sergei]

Have you installed the correct seals and right way?
What about lines, are you sure rear goes to rear vice-versa?

Front should be first circuit and rear should be second on RWD vehicle (although I am not 100% sure if it same for AE86)...

[Dell'Orto]

Yep followed the manual to a T. Yes the front line is fed by the line off the front of the m/c, and the rear from the second line closer to the reservoir. It actually says F and R on the m/c so I can't $&#$% it up

[Stott69]

Id try removing the lines from the caliper and eliminate weather theres crap in the lines

[fangsport]

is the forward piston assembly been reinstalled the correct way? dosn't affect the seal orientation, but does affect port alignment on some M/C's

[Adoom]

Id try removing the lines from the caliper and eliminate weather theres crap in the lines

This, or try remove the line from the master cylinder to the front brakes, does it pump fluid out of the master cylinder? Then work your way towards the callipers till you find the failure.

[Dell'Orto]

. Even with the front brake pipe undone from the m/c the pedal stays rock hard.

[Dell'Orto]

is the forward piston assembly been reinstalled the correct way? dosn't affect the seal orientation, but does affect port alignment on some M/C's

I'm fairly certain it was - I had 3 others to pull apart to compare...I may have to strip it down and recheck though.

[fangsport]

is the forward piston assembly been reinstalled the correct way? dosn't affect the seal orientation, but does affect port alignment on some M/C's

I'm fairly certain it was - I had 3 others to pull apart to compare...I may have to strip it down and recheck though.

done it on a mate's stockcar.......... not they need brakes with a bumper like that !!

[matt dunn]

can you swap the two outlets on the master cylinder to try,
probably wont solve the problem but will tell you if it is the MC or not,
as it should bleed the front and not the back then.

[Crucible]

Edit..

I just re read your post.

Do you have flow from both ports with pipes disconnected?

[Grrrrrrr!]

Did you put the little bolt on the side of the master cylinder that holds the front piston in before the front piston was far enough forward? try taking it out then pushing the pedal in a bit, then tightening it up.

When you bleed the rear circuit does the pedal go all the way to the floor or stop after not much travel?

[Quint]

Have you installed the correct seals and right way?

This.

[allencr]

MC is F'd up, assembled wrong.
Pedal wouldn't go the the floor if that little piston stop bolt was in the wrong position, so you've got a seal or piston in backwards, or if new pistons came in a kit, check against the old ones.

[Dell'Orto]

just re read your post.

Do you have flow from both ports with pipes disconnected?

Not really, maybe a dribble from the front with a geyser from the rear

Did you put the little bolt on the side of the master cylinder that holds the front piston in before the front piston was far enough forward? try taking it out then pushing the pedal in a bit, then tightening it up.

I did notice the day after installing it that it was leaking from the stopper bolt, and it was quite loose. Today at lunch I stripped it and reassembled, and with the piston assembly compressed right up, I reinstalled the bolt but it seems to have made no difference. Unless I wasn't compressing it as much as I though?

When you bleed the rear circuit does the pedal go all the way to the floor or stop after not much travel?

Hits the floor

MC is F'd up, assembled wrong.
Pedal wouldn't go the the floor if that little piston stop bolt was in the wrong position, so you've got a seal or piston in backwards, or if new pistons came in a kit, check against the old ones.

That's what I'm leaning toward...however I've got 4 identical m/cs to compare it to, and the seal orientation appears to be the same. Pistons are definitely in right. I do wonder if perhaps the seal kit is slighty different? I used a kit from BNT, perhaps I should get a genuine kit and see.

[crispy'86]

it won't take much if the seals are slightly larger in diameter, Measure the piston, the bore size. Seems like something is blocking off the outlet port for the front lines.

[Dell'Orto]

So not 100% sure how, but I've fixed it...I either had the springs the wrong way around (There is a long one and a short one) or this time when I reassembled it I paid close attention to how far the front piston assembly was down before I wound in the stop bolt.
Either, way brakes are mostly bled and we're good to go