Which 7/8 master cylinder?
Is it possible Im introducing air back into the front(radiator side) primary port (front brakes on wilwood) after its bench bled by bleeding the back brake lines first? or is it even possible to get air back in the master after its bench bled while pumping to bleed the lines?
Yes it is
That is why the M/C usually comes with the little plastic fittings and cheapo rubber or plastic lines. The idea is to keep the lines submerged during the procedure, and if you see fluid going back up the lines, you have to pinch the line to prevent that, else you'll just be shuttling the air back and forth.
The compensating ports are at the rear ends of the chambers, so I drop the front down a hair while just tickling the pushrod. When the tiny bubbles stop coming out, then I elevate the front end and continue, until no more air comes out. I pinch the lines on every back stroke, to make sure the pistons have to suck in fresh fluid through those little tiny ports.
Once that's done and the m/c is mounted back up with the lines back on; then you still have a little pocket of air to get rid of right inside the outlet ports. I have a helper push down on the pedal while I crack the lines. As soon as the exiting air stops gurgling there, I quit, and;
Then I check for a high hard pedal.
If I don't get it, then I have to move on to the slaves. and then,
As soon as the pedal gets hard, and rests up against the stop, I quit bleeding.
As to which end first?
I always bleed the rear drums first, cuz they allow a longer stroke to purge the air which makes it go faster. Remember that you are pushing air downhill, and it's not always happy about that, so the longer strokes push the air further, and shortens the time for it to try and come back up hill.So you have a better chance of getting it down to below the floor line. Once down there, it's usually not a problem pushing it to the back; and once there, it's all uphill to the w/c's.
Theoretically, it shouldn't make a difference.
done.
