Abs is still on. i have new pads and master cylinder.

I was told by a dealership that the pedal fade is normal. GM products do it too. Replaced the master cylinder on a '93 GMC pickup owned by company owners son because of the pedal fade. The was told it's normal because the new one did the same. I still have that master cylinder in a box in the archives, because apparently it's still good. Ask the mechanics at a dealership about this situation and how you've changed things to no avail and see what they tell you. Good day.

Best case scenario bad vacuum pressure to the brake booster. Worst case bad abs control module or valve body/motor the abs system works by add and removing hydraulic pressure through valves and electric motor. Try using block off plugs at the master cylinder( remove lines plug outlets at master cylinder) check if brake pedal position and pressure is good(if there is no change problem is master cylinder or brake booster/ vacuum) if plugging at master cylinder solved issue repeat procedure at abs valve body after reinstalling lines from master cylinder if your problem returns your issue is in the abs valve body if plugging at the abs solves problem reconnect at the valve body bleed each line one by one testing between each line until you find the problem

Did you bench bleed the MC before installing it? If not, that's the problem. MUST be bench bled or you'll always have air. If brakes lights are on, the brake switch is out of adjustment OR (since you replaced the MC), the push rod is out of adjustment

Was kinda wondering what the ABS problem is. The Master cylinder should be pressure tested as a start. On some models the rod in the power brake booster is adjustable. If the Booster rod does not have some slack in it, your brakes will not be completely off. It is also possible that the Master cylinder is not returning to the Neutral position because the pistons inside the Master cylinder are hanging up.

When you pressure test a Master cylinder you will find the fluid pressure from each port in the Master cylinder. You will also see if there is zero pressure when the Brake pedal is not touched. So this clears the problem to the next testing area. The ABS unit. There are diagnostic plugs for the ABS which will describe a problem and it will be tested Electrically. The same problems about sticking pistons that can be in the Master cylinder, can also exist inside the ABS unit. You mechanic may want to pressure test each one of the ABS ports.

By this point you should have some idea how much pressure is going to the back and front brakes.
You will know if the back brakes are fully functional or not. The only thing left after this would be hanging Calipers that do not return to a neutral position. I am sure you know the feel of Warped Rotors. They can be a sign that the Pads are always dragging.

Front wheel bearings. Often overlooked for Brake wear, if the wheel bearings are too loose the Rotor will not run Perpendicular to the front spindle. The rotors can "canter" slightly and rub the pads.

Take a look at the NAPA rotors on their first line parts. Check the thickness of their cooling fins on their rotors and the amount of metal on the rotor surface Try to get Lifetime Warranty pads from whomever you use. These 2 things will save you money in the longrun.

I hope I have given you some new ideas to fixing your Van. Thanks for using Fixya.

more like the master brake cylinder which is a tandem type cylinder

There is a special tool required to bleed the brakes, it plugs into the ABS hydraulic control under the hood and holds the ABS valves open to remove the trapped air during bleeding, u will need to have the dealer bleed the brakes, they are most likely the only ones that will have this special too, but u can try an outside shop, I am sure Snap on tools makes this tool in the aftermarket tool catagory..

I would replace the MASTER CYLINDER. BLEED AIR from master cylinder BEFORE INSTALLATION. Hope this helps

Sounds like need new Calipers for front too. Maybe a new master cylinder may be need too. Sound like to Calipers or master cylinder are now letting to brake fluid go back to the master cylinder.

the master cyl must be filled and bled before install.after installing new bled master cyl,bleed all calipers.once you are sure there is no air left in system then you will need a scan tool to perform a abs service bleed.if you do perform the abs service bleed with a scan tool the brake pedal will be soft and start to fade.

You may have air in the brake system, bleed all 4 wheels in this order: RR,LR,LF,RF, check the brake fluid often when bleeding, do not let the master cylinder run out of fluid, if this doesn't cure the issue then your master cylinder maybe going out.