[cleansquare]

I'm having the exact same issue. As far as I know the booster is not adjustable, at least not the one I bought.

My brake light has been on in my 85 for about 6 months. I didn't know it was indicative of q bigger problem, thought it was something electrical.

Finally checked the master cylinder, the front brakes were full but the rears were bone dry. Filled them up, bled them and eventually got fluid but no pressure.

Couldnt tell anywhere that the fluid could have gone. NOTHING was leaking, or wet. I bet that it had long since dried up.

Replaced the master cylinder and bench bled it, no change. While in the process figired out my old one had leaked and that's where the fluid went. Changed the booster, no change. Brake light on amd still no pressure to back.

Heard about the front combo valve. Also the rear proportioning valve. Removed rear and cleaned it, no change. Read up on the front one, apparently it has a valve that whej one system fails (rwar in my case) it blocks off that system and allows you to use the frobt still. So I've been running on front brakes only for months.

Tried all the methods to reset it, nothing worked so I removed it, ordered another one from online and got it in last night. Brake light went off, pressure came back to the rear, truck stops better, but still a soft pedal. Does like you are describing.

Bled the brakes till I'm blue in the face. No air...mc, boostet and prop valve all new. Adjusted rear brakes. Dont know what else to do. Stops better now, but still a soft pedal!