I have a 91 k1500, the caliper seized up on it and i replaced all the front brakes(rotors,hub,calipers,pads) the only calipers the local parts place sells if the "heavy duty" calipers which had a larger piston, didnt think this was a problem, everything bolted right up like it should bled the brakes. Had a good pedal that builds up pressure when you pump em when its off, turn the truck on pedal hits the floor. It seems like it has air but i bled the crap out of it and even ended up replacing the master cylinder and brake booster. still hits the floor when it fires up

When the pedal is all the way down when the trucks on the red brake light comes on. Im out of ideas, idk if its because of the larger caliper or because something is broken like abs? Any help would be great thanks guys

 

I have to ask this, but the bleeder on the caliper is up top correct.

I've seen many vehicles come in with calipers installed on the wrong side.

 

Yes calipers are one the correct side

 

The HD brakes have a different master cylinder for more pressure to the brakes. If you haven't changed the rubber hoses for stainless braided hoses....might want to do that.

ABS will not cause the issue on the front brakes as the ABS only does the rear.

 

Youve still got air in the lines. If you gravity bled, its not as quick as it seems. I did a rear disc brake conversion and a front caliper rebuild when i did a 3/4 ton axle swap on an 85 K10 and then i gravity bled it. I started with the caliper nearest the reservoir then worked my way one at a time in order to the one farthest until each caliper dripped clean fluid. Gave the pedal a press and it went to the floor and the brake light came on. Cant let your reservior go empty because you just put air back in the lines. I went back and cracked each bleeder one at a time in the same order and tapped the caliper and any lines near it that i could reach that were parallel or close to parallel to the ground with a small hammer. Tap, dont whack. For all 4 calipers, i had bubbles that were trapped in the lines and/or calipers (most likely the caliper) come out into the clear tube i had presses on the bleeder screw. I had to be patient but eventually the bubbles stopped. This time i had pedal but it was soft. I had to stop to cook dinner so i just tightened them all up. Next day i took it for a ride in a flat field next to the house. It stopped fine and eventually the pedal got firm. That was a year ago and it hasnt went to the floor once. Youve still got air in the system.

As someone else pointed out, the larger caliper will have more holding power than the old ones so your front vs rear stopping ratio may change without changing the proportional valve. I kept the same booster and valve and just check pad wear every so often. It stops fine and the rear doesnt lock up so i called it good.