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?

[LNP]

The brake light cold be on because of the parking brake pedal switch which would be why no matter what you do the light stays on. Its not unusual for the brake pedal to push back when just sitting still idling. Are you sure the combination valve you have is correct for your application? You could also still have a issue with the master cylinder. When driving and then hitting the brakes hard its normal for the vehicle to nose down as that represnts a panic stop. They're not like todays ABS brakes. Is this a disc drum setup?

[Dashman]

Just to Update for any persons searching for remedies to their brake issues. What I've learned about combination valves, contrary to some, is that the differential valve does NOT shut off fluid to the front or rear in the event of a break in the brake line. The brake system is already split between front and rear brakes at the master cylinder. During a malfunction or leak, one side continues to operate normally, while the fluid is leaked out of the other side. The differential valve and brake warning light is what tells the driver something is wrong. The metering valve delays the front brakes, and the proportioning valve reduces the pressure to the rear brakes to keep them from locking up for the most gradual braking events. With all that said, the differential valve will reduce the flow of fluid through it, if it is tripped to that side.

I removed my master cylinder to verify that it wasn't leaking internally passed a bad seal. The seals were fine, and the bore was too. I reassembled and bench bled it again. This time I bent up 1/4" and 3/16" lines that I had left over with vinyl tubing to drop into the bowls. The tube nuts make it easy to switch to the actual lines or to plugs, rather than plastic adapters that will you will have to untwist the vinyl tubing as you're unthreading them.

I also rechecked the booster rod length. It had some clearance, but the end of the MC piston had 45 degree tapers. I had filleted the end of the rod, but not enough nor chamfered to match the taper of the piston. So the rod was in contact with the piston when at rest (no gap). I took 0.019" off the rod and chamfered the edges to 45 degrees for a gap of 0.024" (recommended gap is 0.020"). I had a cutting disk on my angle grinder and it was too aggressive causing material to come off too fast. A 200 grit sanding disk would have been better. I created the angle to match the piston on a stone grinding wheel with the angle marked on the resting tab. I checked the gap with 3 layers of aluminum foil, installed the master cylinder to the booster, removed it, and measured the thickness of the aluminum foil. It may have been rigid enough to depress the piston, but if the thickness is close to the gap the foil will compress slightly. I didn't have clay on hand, and I had already done the measurements and math with a Vernier caliper.

I bled the rear brakes with a helper, there was a jet stream of fluid, and the pedal got firm finally. The fronts didn't move fluid that well. The differential valve was still tripped and illuminating the brake warning light. I started the engine and pressed the pedal slowly until it bottomed out a few times. After like 3 or 4 times the light flickered, a couple more times and it turned off. I didn't have my helper, so I tried to vacuum bleed the fronts. I noticed the bleeder screws were loose, and the seats had grooves around them, and one had some damage to the hex head, so I replaced them. I was getting fluid leaking past the threads and vacuuming air past the threads. I switched to a one man gravity bleed apparatus, and saw steady fluid with no bubbles. I test drove it, the brake warning light stayed off, and the brakes felt much better.

I had purchased remanufactured calipers to save some money, I believe that the bleeder seats are no longer any good, and the threads have lost some material to corrosion. I would recommended new calipers for sure.

The brake pedal with hydro boost still whines when the pedal is depressed fully, but it doesn't pulsate as much. I believe it's time to replace the steering pump with a unit specifically for hydro boost and not just power steering. I think I bought this pump at a salvage yard thinking it may be good.

I found it very strange that only one member responded to me as if I wasn't worthy of advice. It's ok, I got it figured out at my own pace with what time I had available to work on it. I may be an amateur mechanic, but as an engineer I am still a problem solver. One member chose to degrade me in a private message rather than to respond to my post in an effort to help me as the professional mechanic and expert on brakes that he is.

[howzzzit]

I can't address all your problems, but maybe your rear brake issue. I just replaced the rear drum brakes on my 72 C10. Adjusted the shoes and put the drums on. Repeated until I thought I had sufficient drag. Went for a ride and not much rear braking. My parking brake went almost all the way down and it was solid before. It wouldn't stop forward motion with a little throttle. I ordered a brake gauge on Amazon and proceeded to put her on jack stands and remove the wheels and brake drums because I like to do it. Not. With the tool I measured the inside of the drum and locked it. Turned it over and measured the distance of the shoes. Quite a bit off. I don't know if the new brakes seated or what. Ran the adjuster out to where I couldn't get the drum on and then gave it some opposite direction for the proper drag. Went for a ride and brakes work great. Parking brake works like it should. How is your parking brake working? On your valve you can remove the brake light switch and look down in the hole. If it's centered you will see an indentation. Also, there is a tool you can buy to keep it centered while bleeding. Worked for me. Hope some of this rambling helps you. Anyway I thought something was up because of my parking brake and I was right for a change. Good luck.

[Dashman]

I did have the rear up on jack stands recently when I was adjusting the rear shoes. I turned the star wheel until I had just a bit of drag while rotating the wheel by hand. I will do it again to see how well the rear brakes are working, and see if I need to adjust the shoes a bit more.

I've seen the tool to hold the differential valve in place. It would have been nice to install that before trying to bleed brakes and thereby tripping the valve. At this point, I'm not seeing the warning light coming on, so I think the pressures have equaled out enough that the valve isn't going to trip again. I think they could be better, so I need my helper back to try to bleed the fronts again.

Part of my issue is that circa 2000 for my '81 K20, I replaced the vacuum booster, master cylinder, wheel cylinders, and calipers. My Dad helped me bleed the brakes, and everything went off without a hitch. They worked incredible, could lock up at 45 mph, skid straight, and release while still going 45 mph, hahaha. I think those were exceptional brakes. So this is my first experience encountering difficulties. Now I understand peoples frustrations.

Thanks for your response! I am going to adjust the rear shoes again.

[PbFut]

Remember, once relatively adjusted, the rear brakes will self adjust. You need to be moving the truck in reverse and on the brake moderately. When the truck stops, allow it to settle. That action will allow the self adjusters to ratchet the adjuster wheel. The brake components need to be in decent shape and not frozen with rust for the self adjusters to properly work. You should not need to manually adjust once initial adjustment is found.

[Dashman]

I did remember that, and did some reverse stops last evening. I didn't hear any clicking, and I didn't go for another test drive. They felt better, so I stopped thinking about it. I figured I needed my helper to bleed the fronts again since vacuum bleeding was pulling in air past the bled screw threads. It's behaving as expected now since replacing the Bendix 411 combination valve and grinding down the booster rod for proper gap. Thank you for your response!

[geezer#99]

I see you mentioned drilling a new hole in the brake pedal.
What pedal ratio do you have now?

[howzzzit]

PB is right about the self adjusters. Mine were off far enough it would take the self adjuster quite a while at one click at a time. Anyway concerning pulling air with your vacuum tool. Are they very small bubbles like a slight foam. Either leaking at the base of the bleeder or your hose connection. Guys on here have suggested putting a small blob of grease at those locations. Cures the leakage. If your like me you can't find a helper unless they want you to be the helper.