What I generally do on a caliper that doesn't want to get fluid, I have a second warm body, park them in the drivers seat, have them pump the pedal, while I crack the bleeder valve open a bit, and just hold my finger over the end of it, so it can't suck air. (if these are relatively new calipers, some teflon tape around the bleeder screw threads is a good idea. )

 

Just saying, I have a mityvac and think it sucks. ..... It never did work right for me and thought it was a waste of $$ .... then I pulled it out of the drawer to try to use it .... the back of the gauge was cracked as if it froze and cracked ...... I do not understand how brake fluid will freeze and crack ..... possibly it was always cracked and just got worse?

Anyways I have talked to others and they never had good luck with them either ..... I use my wife to work the pedal when it is time to bleed brakes .... she knows the routine, 3 pumps and hold it.

 

I had one of the cheap plastic versions, and used it for years. Worked pretty good, if I could get all my connections to seal up.

 

As far as vacuum it works great. I don't remember if the gauges is inches of water or mercury but I can pump that all the way around to max 25 or 30? soon as I crack the bleeder is drops to zero and I cant pull 5, tighten the bleeder it pumps up again. I don't think there's any issues with the mighty vac, its something in the system. What's funny is the first time I left the front cylinders loose and bled the rear axle, passenger then driver. Both front calipers were running fluid by gravity, I thought sure it would be a couple pumps to get the last bubble and close it up.

In this situation having the master loose is different for me. Just changing calipers by myself its never failed to gravity bleed the calipers if they're empty. Pump the pedal a few times myself and run around and crack, pump crack repeat, 2 or 3 repetitions of this on my own 100% success rate on bleeding brakes.