very weak brakes

I'm new here and have been searching the threads for brake problems. I bought a 1999 cherokee sport last month. When I went to have new tires put on and the alignment done, I was told the front axle was bent. I checked it with a tape measure and sure enough, the passenger side axle tube was bent up a half inch at the knuckle compared to at the differential. Anyway, I scored a free axle off another xj, I believe 2000 or 2001. In the swap I also swapped calipers since the new axle had 44,000 miles on it and my 1999 has 140,000. Well I didn't find this site before I did the swap. When I compressed the piston I didn't open the bleed valve, I just took off the brake fluid resivoir cap. My problem is that I have very weak brakes, the pedal goes all the way to the floor and I get no build in presure by pumping the brakes. I gravity bleed all four wheels and had my wife pump the brake pedal as I bled each wheel, LR, RR, RF and LF. I did get air bubbles out while bleeding. But I can't get the pedal to firm up. Please Help!!!
Thanks, Tice.

More bleeding, I'm afraid.
Review your bleeding technique to insure your not chasing your tail. Have the wife pump 3 to 4 time SLOWLY, then hold pressure. You break the bleeder screw just for a a second--you don't want the pedal to go to the floor. So you tell (ask) your wife to short stroke it, but you can try to control what she does but not leaving the screw open long enough for the pedal to go to the metal. Why not, you ask? Well, an old MC can build up corrosion at the end of the bore, since the piston rarely goes there. If you move that piston all the way to the end, you stand a chance of destroying internal seals when they encounter the corrosion, rendering the MC ineffective herein after.

If the brake pedal has already been pushed to the floor and the seals in the m/c are destroyed, what would the symptoms be? I'm worried because I drove the jeep and pumping the brake pedal did not build any pressure, the pedal did not firm up when pumping. The check engine and brakes lights are both on in the dash. Is there a way to check for codes without a plug-in code reader?
Thanks, Tice

Not sure if it was a typo, but you need to start with the wheel farthest from the master cylinder. So - PR, DR, PF, DF. As to releasing the bleeder screw, I have only done that once - on a S-10 Blazer with anti-lock brakes. With all the rest I have only opened the MC to press the pistons back in. Brake fluid has to go backwards into the MC at least a little or your brakes would stay locked after the first time you stepped on them. Also make sure that you or the person pumping is watching the MC level when bleeding - it's a PITA when you run it dry.

I don't know if it matters, but I know the rotors were different in 2000-2001. The diameter doesn't change, but the hat is composite and the dimensions are a little different. I would assume the calipers are a little different, but not sure that it would alter the pedal feel?

I've read that bleeding brakes on a vehickle equipped with anti-locks requires a different procedure.
I've never personally bled that type of break system, so I'd suggest searching for procedures associated with anti-lock systems.
If the internal seals (on the MC piston) are damaged, the brake fluid will leak past the piston instead of building pressure at the caliper.
The brake light on the dash tells you one circuit in the system has no pressure. There's a valve built into the combination valve that sets dead center if both circuits (front and rear) are exerting the correct pressure. If on circuit looses pressure, either from no fluid or from air in that circuit, the piston moves to one side, completing the electrical circuit that turns on the dash light.
If you only opened the front circuit, when you changed calipers, you probably do not need to bleed the rears, unless, while you were bleeding, you let the fluid level in the MC get too low; In that case, you have air in all circuits, and your job has just increased 4-fold.

I didn't see anyone mention it, you do have the calipers on the correct sides? The bleeders should be on top.

X2 Lawson. I know this from experience. Had someone else throw on the new calipers and pads while I was at work.
Couldn't get the system to bleed properly, even after doing an overnight gravity bleed.
About the time I was ready to put a wrench thru the windshield I thought. " let me try swapping calipers from from one side to the other, because I had noticed that the drivers side pumped more fluid when bleeding, lets see if it's the same on the pass. As soon as I put the pass. side on the drivers side I could see the diff. in the position of the bleeder. I knew right off that was the problem( bleeder was now higher so I could get all the air out). Bled the system again and have the best pedal of any XJ I've ever driven, about 1" of travel.

You guys are great! I love this forum, without your help I would still be going mad. It turns out that I am just an idiot. I had the calipers on the wrong sides. I swapped them around, gravity bled the system, I was alone, and voila! I have brakes! Again, thanks to you all!
Tice Umberger