It sounds like your mechanic may not be retracting the rear caliper pistons properly. The best way to do that is by using the adjusting screw at the back. Some have done it by twisting the piston from the inside end but I've never had any luck with that . You take off the nut then adjustment lever, seals and turn the shaft by hand and the piston will retract into the bore. If you try to use the brake piston compression tool you will damage the caliper internally. IMO, the Fiero rear breaking system leaves quite a bit to be desired but you can get it to work with a bit of fiddling
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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "