Bleeding Bubbles

Now, I'm not a professional mechanic, though I play one on TV, but this is a new one: '81 TD. Master cylinder replacement. Done more than my share of them
on other cars. Never had a problem. So, I put on the new cylinder after a bench bleed, stick the vac sucker on the rear, left wheel nip, suck until no bubbles. Do the same to the rear right. Move to right front: the bubbles do not stop. Remove and rebleed the MC. Reinstall. Bleed the back-no probs after about 2 cups of fluid. Bleed to the front right: nonstop bubbles. Pressurize the MC through the filler cap vent hole. Again the rears are great. Ran a whole quart of fluid through the front right and it never stopped bubbling. Removed the MC and re-bench bled. Noticed the rear, passenger side fitting was sputtering fluid during the bench bleed when the others were doing the fire hose thing. For the life of me (quite literally, since these are the brakes) I can't see where the air is getting in. My guess is the new MC is bad and is sucking it in through the back. Before I take the MC back I'm gonna get the good MC offa my wrecked '83 DT and see if it does the same thing. How'm I doin'? Any comments appreciated. Thanks.
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You get an "A" for effort!
Suggest you have an assistant help you bleed the brakes the old way - pump the pedal and hold while you bleed each wheel's caliper. I believe you'll soon find the leak for it will then be a fluid leak.
In addition to the "new" master cylinder, I'd pay close attention to the right front brake hose and caliper piston.
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Just to back that up Tom, I agree. Always do it the old fashioned way, and always put new pads in the slots. You need to get the pistons all the way home to make sure there is nowehere for air to lurk. Using one of those compressore gizzmos through the reservoir filler just compresses that trapped air against the back of the piston (if it is out a little) and you never get it out. The air can still remain trapped there even with the old fashioned way. New pads is the best answer. Alternatively If you don't want to fit new pads, I lever them back (both pads - got a nice flat cold chisel) and wedge them back with a screw driver whilst I bleed. A little bit of fun for you and the wifey. DOWN..... down........ UP...... up..... etc. Just make sure she sits still so it doesn't fall off the jack!
Cheers... Rob.

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Thanks for your responses. I'll try the old MC tomorrow and see how that goes. These brakes are still les of a pain than my old Harley banana callipers....
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