Proportioning Valve Depressor for ABS Brake Systems ABS Brake Proportioning Valve Depressor The proportioning valve depressor works on various GM utility vehicles, vans, and pickups fitted with Kelsey Hayes anti-lock brake systems. It also works on rear-wheel anti-lock brakes.. Two depressors work best for four-wheel anti-lock systems. No. 7853 – ABS brake proportioning valve depressor. 7853 No -