You changed the brake calipers on a 1993 Nissan pickup cannot bleed the air out of the system cannot find a load sensing valve or bleed valves on the master cylinder Any ideas?
One Other Thing, You May Have A Bad Master Cylinder. I`m Sorry I`m A Littled Mixed as To How You Are Doing This. Hope You Get It Done. You Bleed The System Through The Calipers. Fill The Master Cylinder. Go To The Passenger Side Caliper Loosen The Bleeder On Top Of The Caliper. And Bleed as Much Air Out Here As You Can. Go To The Other Caliper And Do The Same. If You Replaced The Calipers Both At The Same Time As You Removed Each One. You Will Need To Bleed The System A Couple Times Most Likely. This Should Do It. Answer If vehicle is fitted with a load sensing valve it may be the fact that it is restricting flow to the front brake calipers and preventing a full purge, most lsv's do not effect the front brakes but the japeneese seem very fond of it.
Either adjust the lsv to fully open position or try bleeding the brakes with the vehicle quite laden.
It is worth ensuring that the piston in the lsv is actually moving when the brake is applied as they often stick if the vehicle has been run at a constant weight.