First, is the ABS light on? If yes by pass the fuse removal step, and lets not even go there it is out of the equation.
If the ABS light is OFF...before we replace more and more parts...that might still be in good condition and that might cost you money you don't have right now for the guessing game...pull the fuse to the ABS brakes, this will kill that system, once the ABS light displays on the dash, we have just eliminated it from the equation....what equation you ask....well what if the ABS was at fault and is the culprit...would't that lock up the wheel if it is sensing trouble, now it is disconnected try it if it works you can leave it alone or spend more money on the fix, when the ABS light is on on any car this means it no longer has that feature, which means the car will now be stopping with regular power brakes not ABS, I have a Mustang for years like this cause it just costs too much to fix it, and it is NOT part of any states inspection requirement.
OK so much for that, next check the axle bearings, raise rear off the ground both sides support on jack stands and turn the axles by hand..feel binding? How about up and down play on the axle hub? If you have bad axles or C.V. joints the rotor will shake and cause the ABS sensor to try to stop the wheel from turning, so any binding or excessive play have the bearing/c.v. joints replaced.
If all that is ok, now we go back to the brakes, check the condition of both rear neoprene rubber brake lines, if they are cracked and brittle(sorry looking) replace them, they have a tendency to collapse on the inside of the hose causing the fluid to lock up the calipers pistons, so check this .... it definately sounds like the brake hydraulic system is contaminated, and the flush was probably a right idea, however it did not complete the repair.
If I were you, I would pull the calipers from both rears and test them in a vise, put a 1/2 " piece of wood trim in between the brake pads(caliper bolted in vise, brake pads back in it, wood acts as the rotor for this test, get it?) If no wood the pistons will come out of there bore and the test is worthless...apply a low pressure regulation of compressed air to each caliper through the brake line port into the caliper...do the pistons apply pressure on the wood? Do they retract when you release the pressure, or are they stuck"frozen"...If so this is your problem...sticking calipers, inspect the rotors for overheating signs of hair line cracks/blueish coloration if they are over heated replace as they may have lost there temper and may have become too brittle.
Always replace brakes as an axle set ...two rotors...two calipers....two disc/drum brake pads.
Below is a laundry list of ABS brake bleeding proceedures to follow only if you replace items other then downstream of the ABS modules...things like wheel cylinders(calipers) brake lines etc...all get the normal brake bleeding.
Here is thearticle I found in sequence for ABS systems:
Anytime the a brake system is opened to replace components such as calipers, wheel cylinders, the master cylinder, or brake lines or hoses, air gets inside. The air has to be removed by bleeding the brakes
if you want a firm brake pedal. Air trapped in the lines, calipers or wheel cylinders will make the pedal feel soft and spongy. Air is compressible, so when the brakes are applied any air bubbles in the system must first be compressed before the hydraulic fluid will transmit pressure to apply the brakes.
As a rule, the brake circuits on most vehicles with anti-lock brakes can be bled in the usual manner, provided no air has gotten into the ABS modulator assembly. If the only components you replaced were downstream of the modulator (calipers, wheel cylinders
, brake hoses or lines), chances are normal bleeding procedures will clear the lines of any unwanted air.
Brakes can be bled manually, with a power bleeder, injector tool or vacuum bleeder. It does not make any difference which method you use as long as all the lines and components are flushed with enough fluid to remove any trapped air bubbles or air pockets.