Brake callipers sticking ,changed callipers and fluid and there still sticking ,back brakes feel fine.

A grinding sound usually suggests metal to metal contact but, as you say, you have changed the pads and disks.

What springs to mind is that that the brake backing plate - the metal disk on the inboard side - are being touched by the spinning disk, or the noise is being caused by a driveshaft or bearing.

However, there are other possibilities. Are there any shims in your braking system? Shims hold the pads in place and stop squeal/rattle.

It also could be that the pads are not being fully released from the disk when the brake pedal is pressed. Depending on your calliper set up it may be something as simple as a slide that is sticking and needs cleaning.

Brake pads are released from the disk by what is nothing more than the spinning of the disk 'knocking' things back. Assisted by rubber sleeves on 'slide pins'. Something may be sticking and need cleaning and a smear of copper grease added.

It would be too easy to say that you have a vacuum leak (or internal seal) problem in the brake servo. A servo problem usually results in a 'hard' brake pedal at all speeds. You don't have this problem.

It may well be that your brakes feel 'spongy' at low speeds because the pads are not being shoved back from the disk because of sticking slides (depending on your system).

It also may be that the pistons in your calliper are sticking.

You obviously can work on cars and use tools - consider overhauling your brake callipers (look on Ebay for overhaul kits) but bear in mind that doing this also means you have to bleed the brakes.

check for fluid leaks at hoses , pipes and brake callipers and cylinder units. Pull the vacuum hose off the booster and check for brake fluid in the hose. (wet). Repair the fault-replace calliper leaks, replace wheel cylinders , replace brake lines and replace the brake booster.

Fill with brake fluid and bleed out starting at the longest line first and finishing at the shortest.

indicates that the calliper slide pins ( the pins that are bolted to the frame that bolts to the axle mount) are rusted up
the purpose of these pins is to allow centralization of the calliper on the rotor on brake application and allow centralization again when the brakes are released with out this action the pad on the outside of the rotor stay in hard contact and makes the brakes drag
next check is the brake master cylinder has a blocked compensation port and that is keeping the brakes applied as the fluid cannot return to the reservoir after the brake application
take it to a brake specialist shop for a proper diagnosis and quote

are you talking about both front brakes sticking.by lines i assume you mean the brake flex hoses.have you checked to make sure that the sliding surfaces are smooth and free of damaged surfaces and the brake pad clips are in the proper places.if so and all this is good that you have done then you could have a master cylinder that is not releasing pressure for the front brakes,or you could have a defective flex hose(if they are not twisted) that is blocking the fluid from releasing the calipers.

for front pads jack and support car remove wheels remove bolts holding calliper [2]remove spring clip pull calliper off remove pads clean housing fit outer pad slowley push calliper piston in using large grips fit inner pad to piston refitcalliper fit bolts refit spring clip can be awkward pump brake pedal until firm check fluid level rear ones are the same but special tool needed to wind calliper pistons back in note make sure brake discs are in good condition first

with car on stands use punch to remove pad retaining pins pull out pads can be tight remove 2 calliper retaining bolts move calliper away from disc remove disc retaining bolts remove disc check hand brake shoes and clean look for adjuster between shoes if it has one back it of some models just have hand brake cabel adjustment clean and fit new disc secure adjust hand brake shoes using screw driver through wheel bolt hole clean refit calliper slowley push back calliper pistons fit new pads refit retaining pins do other side pump up brake pedal check and adjust handbrake if neededcheck brake fluid level

i would try the perportioning valve

hi it sounds to me to be a sticking brake. my advice is to jack up each wheel and check if it rotates. it could be a sticking calliper on the ftont or rear. if it is the back wheel it could be a sticking handbrake cable. try wrigling the cable but make sure the car is secure before going under it.

Do you mean back brake pads or the back brake callipers?
To change pads you need to use a rear brake pads changing tool to screw in the calliper piston or if you are experienced enough you could screw in the calliper with a two mm thick piece of metal sheeting that fits into the grove of the piston.
If you need to replace the whole calliper remove the hand brake cable first and clamp the flexible brake hose remove brake hose, remove the callier with cylinder and then remove the calliper holder. fit new holder pads and locks and the calliper with the piston and the brake hose and the hand brake cable. Bleed the brakes. Mike

it may be that the flexi brake hose is perrished on the inside and not letting the fluid back up the system. try pushing the piston back with the bleed screw out, if this works then a collapsed flexi hose is favourite. if this is a rear calliper then they may be the screw in type, does the calliper have a lever on it for the parking brake.