So, I've been trying to get my brakes bled on my '68 142. The front calipers had some sticky pistons, so I replaced them with some recently rebuilt calipers without sticky pistons. The rears are fine, insofar as the pistons move.

(One of) the issue(s) is that the upper bleed port on the left front caliper will not bleed. In fact, I can pull the bleeder nipple all the way out while stepping on the brake pedal, and nothing happens. If I manually push on the pads to retract the upper pistons, fluid comes out of that upper bleeder. So it's not clogged at the bleed port, but it must be clogged somewhere upstream, right? I just can't figure how an obstruction would allow all four pistons to engage the pads, but not allow pressure to get from the MC to that one particular bleed port.

Any thoughts? The car is borderline undriveable, so I really want to get it figured out ASAP.

Thanks,

Tyler