I cant get the caliper to depress when im doing the rear disc brakes on a 1998 ford taurus

Question edited for clarity.

Did you fit a new shim kit? In reverse, the brake pads can tilt and jam. Do you have room to go forwards a bit? Apply brakes and reverse again.

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If it is a disc brake with the park brake connected to the brake caliper the piston in the caliper will need to be rotated back into the caliper bore. there are special; tools for this but sometimes a multi position wrench can be used. If when rotating the piston starts to move out of the caliper stop straight away and reverse rotation before the piston comes out causing loss of fluid and air entering .

Yes, there is a special tool. Rear Caliper Piston Adjuster T87P-2588-A.

The pistons in all calipers I have seen can be forced back into their seat to allow new brake pads to clear. If constructed as most, a C-clamp can be used to press the cylinder back in.

1. Raise and support the vehicle
2. Remove the desired wheel
3. Loosen/remove the two caliper retaining bolts.
4. Remove the caliper from the wheel
5. Using a C-clamp, depress the caliper piston until it's completely recessed.
6. Remove the old brake pads
7. Install the new brake bads on the caliper
8. Reinstall caliper on the disc
9. Reinstall/tighten the calpier bolts
10. Put the wheel back on
11. Lower the vehicle.

*** When you are getting set let the car roll a few revolutions of the wheel to keep the pads off the disc. It will make it easier to get the caliper off.

rubber brake hoses are collapsed

it could be two things: you have a bad check valve in the master cylinder or the calipers themselves are bad

206-04: Rear Disc Brake 2000 Explorer/Mountaineer Workshop Manual REMOVAL AND INSTALLATION Disc Removal

1. NOTE: When removing the rear brake disc (2C026) in this procedure it is not necessary to disconnect the hydraulic lines.
   Remove the rear disc brake caliper (2552). For additional information, refer to Caliper in this section.
2. Disconnect the brake hose.
3. Remove bolt.
4. Disconnect the rear wheel brake hose (2A442).
5. Remove the copper washers and plug the brake hose.

1. CAUTION: Do not remove the guide pins or guide pin boots unless a problem is suspected. The guide pins are meant to be sealed for life and are not repairable. Use Silicone Brake Caliper Grease and Dielectric Compound D7AZ-19A331-A (Motorcraft WA-10) or an equivalent silicone compound meeting Ford specification ESE-M1C171-A for re-lubing the caliper slide pins. Other greases can swell the guide pin boots, resulting in contamination and accelerated corrosion or wear of the caliper slide pin mechanism.
   Remove the rear disc brake caliper (2552).
   1. Remove the brake caliper bolts (2W303).
   1. Lift the rear disc brake caliper off the rear disc brake caliper anchor plate (2C220).

1. Inspect the rear disc brake caliper for leaks.
   • If leaks are found, disassembly is required. Refer to Caliper in this section.

1. NOTE: If the rear brake disc binds on the rear parking brake shoe and linings, remove the adjustment hole access plug and contract the parking brake shoe and lining.
   Remove the rear brake disc.

1. CAUTION: Use a hub-mount brake lathe if necessary to machine the rear brake disc.
   Measure the rear brake disc, and resurface as necessary. Install a new rear brake disc if beyond specification.

these rotors are known for rusting onto the vehicle. when you removed them you probably had to beat them off with a hammer. if this is the case then you may have a small amount of surface corrosion on the hub. this could cause your rotor to not sit evenly and cause a wobble. recommend removing the new rotor and cleaning the surface of the hub

Unfortunately, the lip seal which your caliper piston rides on is leaking. The only remedy for this problem is to replace the caliper.