When you pull up on the e-brake handle is there any tension at all or is it loose? If it's loose than you have a problem with the cable. Could be broken and needs replacement. If there is tension then it's probably the rear calipers. Brake pads might need replacing, or the calipers need attention or replacing.
2007 Torch Red Mustang GT, Parchment Leather, Saleen Supercharger, SCT X-Cal Programmer,brenspeed.com tunes, Tuned by X-Act Dyno (Tempe, Az) 425rwhp, 4:10 Gears, Axel-back MAC exhaust, Dashhawk OBD-II Computer Monitoring System, Sequential Tail Lights, Halo Driving Lights, Eagle Eye Headlights with 6000K HID's, Clear Turn Signal Lenses, Projector Switchback Bulbs, Painted White LeMans Style Stripes, CDC Aggressive chin spoiler, Billet hood pins, Pirelli P-Zero P255 40 ZR19 wheels mounted on 2014 Mustang GT Wheels