Andrec

Managed to let the fluid reservoir for the front brakes run dry while changing a hose. The car has the original master cylinder (1973) with two bleed screws on the side so I've bled those and started on the calipers.
I'm doing the drivers side and bleeding the front and rear calipers simultaneously to prevent the pressure warning switch from moving.
Trouble is, I've already used more fluid than the capacity of the front brake pipe and fluid reservoir combined, and yet the air bubbles still keep coming from the front caliper bleed screw.
Is there any way air can get back into the system while I'm bleeding the brakes, a faulty master cylinder for instance?
The bleed screws were only undone a quarter of a turn so I don't think air can get back in that way.

JB

I've had a lot of trouble with air getting by the threads on the bleeders, even when they're just barely cracked open enough to let the fluid flow. Other folks have put teflon pipe tape on the threads, but that's a pain & seems chancy to me, given how corrosive brake fluid is. I've gotten to where I don't even worry about bubbles, period--I just pump enough fluid through that I'm sure it's cleared (while tapping the caliper to loosen bubbles), and tighten down the fitting. Works just fine--I've got nice, firm brakes.

JB

Andrec

Thanks for that, I'll try what you say.