Not good enough brakes

[Dashman]

I'm having a few brake issues going on at the same time. I'm tired of thinking about it, and need a path forward towards good brakes.

The history of my Dad's '72 K10: In about 2000, I replaced the rear brakes in the 12 bolt. In hind sight, it was probably the front flexible hoses that were preventing the front brakes from fully working and a bad combination valve. Shortly after, I parked the truck when a number of issues with it piled on. When I started to rebuild it and removed the rear drums, the brakes were like the day I installed them. So I inspected the combination valve, for about 2 minutes and said to myself I have too much to do, and decided that I wanted to keep it so I sent it out for a rebuild. I also sent brake cleaner down the brake lines, blew them out with compressed air, and then sealed them with masking tape.

The rebuild: In 2019, I removed all the drivetrain, and started to rebuild a 14 bolt rear end, the NP205 transfer case, acquired a 700R4 core and sent it out for rebuild, acquired a 1994 roller cam 350 engine, and front end components to upgrade the Dana 44 front end. I bought the proper bracket to mount a 2005 GM hydro boost to the firewall, and added a JB7 master cylinder. I custom cut the rod to have a few thousandths of an inch gap, and drilled a new hole in the brake pedal lever. I placed it half the distance between rod up pedal up, and rod down pedal down. The rod enters the hydro boost nearly level throughout the stroke. So everything is new or rebuilt. I also bench bled the remanufactured Duralast JB7 master cylinder, twice (it lost fluid while the combination valve was leaking).

The startup: When I re-installed the combination valve, it leaked from the metering valve. I disassembled it and found a seal was placed backwards, leak fixed. When I went to bleed the rear the brakes no fluid would come out. That's when I fully took it a part and found broken pieces, so I swapped in a used brass combination valve from an '80s model. Problem solved, I had brake fluid to the rear brakes. During initial engine start up, I flushed the power steering pump with about 2 quarts of fluid. It wasn't coming out clear yet. Some time after, I flushed another 2 quarts. It was better, but not clear. I drove the truck, it braked, but it would nose dive and the braking was not good. I did some more brake bleeding all around, some air came out, and the brakes got a little better. I did find a leak or leaks from the brake lines after the combination valve to their respective tees. I swapped the gravel guards onto new lines, bent, and flared new lines. Currently, there are no brake leaks. I also removed one drum just to make sure that I didn't have a leaking brake cylinder or have the links cockeyed. Everything was fine.

I think I may have damaged the original 411 Bendix combination valve disassembling it, or when I slammed the brake pedal during start up because the transmission was accidently started in gear (it was instinctive). Tested the neutral safety start switch, and fixed that issue. The shift lever wasn't getting into park, and I thought it was in neutral.

Issue #1: The brake light stays on. I checked the switch by placing the body on the battery ground terminal, and applied a test light. No light. Then I used a pair of vise grips to hold the switch closed. Light. So I think the switch is good. I also tested it on the combination valve, and the test lamp lit. That tells me the differential valve is tripped one way. Probably towards the front. I found a method on here to trip the differential valve the other way. I connected a 3/16" vinyl tube from the left front bleeder up to the master cylinder. I left that front bleeder open while the rear bleeders were closed. I pumped brakes slowly, but the dash brake light never went out and the brakes never felt firm.

Issue #2: The rear brakes are not getting firm. I vacuum bled the rear brakes initially, and got a lot of bubbles out that way. I two man bled the brakes all around. Then I one man bleed the brakes again for the 3rd time. With each bleed, some air came out, but not much. I also placed the rear end on jack stands, and adjusted the rear star wheels to just get contact with a hand turned drum. With the engine on, the brakes were having a hard time stopping the rear wheels. ...too much brake effort. There are no leaks, except from the bleeder screws when I open them 1/4 turn.

Issue #3: With the engine on, the hydro boost brake pedal was pulsating when I would depress the pedal near the bottom of the stroke. I had the front end on jack stands, and turned the wheel back and forth while stopping to add steering fluid. When I drove it initially there was some pump whine, and difficulty turning. I would add some fluid, and the whine would go away. Currently, it's only whining when nearing full turn, on asphalt, at slow speed. Do the return lines in the pump reservoir need to be well below the fill line? One of mine return ports enters just about 1" below the fill line. I used JIC fittings to connect all of the steering and hydro boost hoses.

I'm thinking I should replace the combination valve, and maybe that fixes the brake light issue and rear brakes not getting firm issue. Like I said, it's a used combination valve. ...or could it be a bad master cylinder? I never pushed on the cylinder until it had brake fluid. Also, maybe I should replace the steering pump. It's also used, and of unknown condition. Is there anything more should do, before or after buying these components?