How hard is it to replace brake line front or back both please

You will need to bleed the brake system. I would start with the rear brakes lines and work towards the front.You must have key off engine off when bleeding brakes, apply pressure on brake pedal 10 times and hold. The brake line is now ready to be open. Open and let the stream of fluid come out and close the line tight. Then release brake pedal once bleeder screw is close. This procedure must be repeated twice front and back. After, brakes have been bleed pump the brake pedal before putting in drive.
Note: Don't let the resevoir run low on brake fluid. This will cause air bubbles to accumulate on the brake system. Always top off before opening bleeder screw.

check your master cylinder

Hi, if you plug the port, the plunger will not be able to build pressure in the front lines as the back brake section of the master will hold the plunger back. The proportioning valve will also not let you do this, as it is trying to strike a balance between the front and rear brake pressure. I'm afraid you need to repair the rear brake lines. This is not hard work, but it does require a brake line tool for cutting and flaring the lines. You may be able to borrow the tool, or check to see how much a brake place would actually charge to replace the lines. The supplies are cheap, and the labor isn't really very long--maybe a couple hours.

check for front brake calipers dragging, if the are replace calipers and front brake hoses, if calipers ok replace master cylinder, This is how to check calipers, jack up front of truck have some one apply brakes and release as soon as they release the brake peddle the wheels should spin freely if not brake the brake line lose at master cylinder if wheels spin free with line loose replace master cylinder, if not replace calipers and hoses.....HOPE THIS HELPS

It has to be your proportioning valve, and it is probably jammed and blocking flow to the rear. You can either replace the valve or try to reset it. To reset, you need a way to put pressure into the rear brake exit port. If the valve has bleeder screws on it, try opening the front bleeder and pumping the pedal. If there is no bleeder on the valve, I have also heard of people opening the front caliper bleeders and pumping the brake to see if a little pressure in the rear will slide the piston open. No harm in trying these ideas before buying a new one, eh.

ok sometimes a cylinder can be turned try this open bleeder cap on front left side then slam on the brake pedal as hard and fast as you can this will sometimes turn it back the right way. if brake fuild comes fling out it worked. when you bleed then use a hose to go on the end of the cap and the other end in a bottle of brake fuild so it cant get air back in the line. good luck

You need to replace the round Ball (accumulator ball). It's not holding pressure. You have front brake only. Is the pedal hard as a rock, the red brake light stays on, abs light stays on?
Check out this sight. http://www.albeedigital.com/supercoupe/articles/abs-system.html

Brake fluid is highly corrosive. If you can't get the line loose on the frame side then I would suggest replacing the hard line as well coming from the master cylinder. Or if you have a flaring tool you could cut the hard line just behind the rubber and put a new fitting on it. Pretty easy if you have the tool. Essentially you will wind up kinking or breaking the hard line anyway if the fitting won't come loose easy.

Check out this link & read about combination valve & how to center it when bleeding.

http://www.autozone.com/addVehicleId,1321403/initialAction,repairGuide/shopping/repairGuide.htm?pageId=0900c1528007a632

Itcould be that the brakes installed on your car were not the Original Manufaturers (OEM) recommended pads and/or shoes on the back and front. Or only two of the brakes were replaced. when installing breaks install the OEM's or original breaks for your Corsica.
If a given set of replacement linings are more aggressive than the original, the brakes may feel grabby or upset front-to-rear brake balance increasing the risk of the front or rear brakes locking up on wet or slick roads especially if the more aggressive linings end up on the back brakes. On the other hand, if the replacement linings are less aggressive than the original linings or have less fade resistance, the vehicle may require increased pedal effort and take longer to stop than before. And if these linings end up on the front brakes, they may increase the risk of rear wheel lockup, too.