Car is power brake disk drum, everything is new, brake pedal occationally will not return after applying brakes. When this happens brakes stay applyied until I reach down and manually pull brake pedal up with my foot. Any ideas why this happens? Thanks for any advise!

Pedal linkage to tight or binding?

booster/check valve prob but I would 1st split the booster/mc & check the pushrod clearance to the bottom of the piston recess, want ~1/8", maybe a bit less

unplug the vacuum line to the booster. try again.
if it still stays down then I would check for something binding.
if it doesn't then I would bet on the internal check valve.
had one suck the brakes to the floor while I was driving on the freeway.
gradually pulled them down and I kept applying power till I realized my gas pedal was on the floor and I was barely keeping up with traffic.

Thanks for the input guys! I'll look into those items this weekend and see what I come up with.

Well I know it's been a while since I asked about this brake issue, but I finally got to working on it and here is what I got. Replaced booster, mc, checked all linkage, etc.. After replacing booster pedal doesn't stick down, but now I hardly have any brakes. New mastercylinder went on at the same time which was bench bled and bled brakes at all 4 corners. Problem is as you pump up brakes they intially go to floor then will get hard mostly to top, but after stopping for a few seconds and pumping again they go striaght to floor again. They are actually worse than before with the exception the pedal hasn't stuck down yet. I am thinking I still has air trapped somewhere but no matter how much we bleed them I can't get any air out, in fact I only got air out of the left rear and that was the first crack of the bleeder then no more. Any ideas will be very appreciated! Thanks moparts!

I am not exactly sure what you are referring to on the proportioning valve? I have never messed with it during the bleeding process?

If your prop valve has it it'll b a little pin w a rubber boot. If so might need to pull/hold it out so the fronts will bleed

Pulled pin out (only came out app. 1/8") tried rebleeding all 4 corners but still no air and brakes are the same. Any other areas I could be overlooking?? Thanks again for any advise!

Make sure your calipers are not mounted upside down. The bleeder valve should be on top.

I'd start back at the beginning and get (2) brass inverted flare plugs from the Edelman" fittings cabinet at your parts house. They're cheap and the end will have an inverted flared "cone" a mirror image of the brass seat(s) in the M/C ports. Cap the M/C & if it good (& bled out) the pedal will b rock hard w virtually no travel. this'll elim the M/C & you can concentrate on the prob valve (blockage of some sort) or one of the 4 corners. "air"

Are the rear brake shoes adjusted properly?

Is the rod in the booster adjusted properly?Thats the first thing to check if you dont have air coming out of the bleeders.That and make sure the PP valve is centered.Rocky