To release pressure from the cable, there is an equalization cable under the vehicle where one cable (from in vehicle) connects to two other cables (one for each side on the rear). There is an adjuster bolt that you loosen to release pressure from the cable.
I have to be honest, the nut on the adjuster is most likely rusted and will break if you force it. Make sure to take your time, take a wire brush to the threads on the bolt, and then spray it with a good penetrating fluid and allow it to soak.
One you loose that, you will be able to reattach the cable at the caliper.
Here are the directions for adjustment once you get it reattached:
1989 Buick Regal V6-173 2.8L
Disc Parking Brake
Vehicle Brakes and Traction Control Parking Brake System Adjustments Disc Parking Brake
DISC PARKING BRAKE
1. Lubricate parking brake cables at underbody rub points and at equalizer hooks and ensure free movement of all cables.
2. With parking brake fully released, jack up both rear wheels.
3. Remove slack from cable by holding brake cable stud and tightening equalizer nut. After tightening nut, check that caliper levers are against stops on caliper housing. If not, loosen cable until levers return to stops.
4. Actuate parking brake several times to check adjustment.
Let me know if this helps or if you have other questions.
Monday, March 2nd, 2020 AT 6:25 PM