by matthewh » Tue Jan 27, 2015 3:04 pm
The valve at the front of the truck is the proportioning valve, you need to keep that. The ABS valve is the hunk of metal at the back or the truck, inside the drivers side frame rail. That's what usually causes rear brake issue with the trucks and that's what you want to bypass.
If the brake system itself has been poorly maintained, or run low on fluid enough for air to get in, its possible the proportioning valve is stuck, bypassing the rear brakes. If that's the case, you really need to start from the beginning and bleed the entire truck. May take couple tries to get it right.
Did you ever get a vacuum reading? I'd start at the pump itself and work back to the booster, checking every connection for leaks. Should be pulling close to 20lbs of vacuum and if the vacuum's low, the ABS and (P) light will be on, due to the vacuum sensor located on the drivers side inner fender
'93 W350 5spd Getrag, 4.10 gears, 83k miles and counting, Mods: LPPP AKA Ma Dually
'54 Dodge M37 6.2/700R4/205, 5.89 gears, WC rear axle