I can't lock any wheels when hard on the brakes on dry pavement. It's a 91' R7U with the PBRs. They will lock in lower traction situations. I just put new pbr's on it and they still won't lock. They grab really good and they almost lock but not quite. Car tracks straight, doesn't pull or or anything when on hard. Lots of feel/response in pedal. Had different pads still no dice. No fluid loss either system is tight and bled. Master Cylinder maybe?

 

both firebirds i have had have slid if you hit the brakes hard enough but maybe my ABS just didn't work in them...lol

 

Probably depends on the brake pads also. I still have the stock 10.5" front brakes on my 86 with a set of aggressive front race pads and can easily lock the fronts once they reach operating temps.