Gravity brake bleed

Have a 78 vette.  recently replace calipers, flushed out the lines with denatured alcohol also replace all other parts that connected to brake lines. Doing a gravity bleed  of lines but only the front right and left brake are bleeding.

Any ideas why the back brakes are not bleeding.  

gravity bleed is usually not enough.........

take a look at this link...

http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-92474.html

most parts stores have brass bodied brake bleeder kits for about 25 to 35 bucks..


i have loosened one bleeder screw at a time...    grabbed the brake pedal.. and pumped it down and up with force... about an inch...  this pressurizes the master cylinder chamber...  just enough to push fluid out..  but not enough to create suction to pull air back in at the calipers...

there are also speed bleeders available..   they need to be just a tiny bit open..  i have seen them used with a single wrap of teflon tape.. just enough to seal the threads lightly to the caliper.. and ONLY on the threads about a quarter inch up from where the threads start...  electrical tape is what i would probably use..

you have to remove the tape before finishing the job...  you also have to make sure that NONE of the tape gets into the caliper... fluid does move back and forth between the calipers and the master when changing brake pads... it can really ruin your day...  and your front bumper ... if you get the IMPACT of what i am saying..

you can do the same job.. with 2 people and a finger over the bleeder screw opening... with the bleeder screw out..   have that person hold their finger tight.. while you pump...  usually with your hand..  the excess fluid will escape... when the pressure goes negative.. if they are holding their finger tight over the hole.. it will prevent the air from being pulled back in...

there are a LOT of ways to bleed the brakes...  the vacuum tool works really well.. and i use it for testing many other things...  i don't like the plastic versions of the hand vacuum pumps.. the brass.. are just far superior..

brake fluid will wash off with water.. except from friction materials..   so you might want to keep some bottles of warm water nearby..