Soft brake pedal, not quite the same as other issues

[earl84]

Sorry this is so long, but I could use some assistance.
I have read many times about switching from manual to power brakes and the associated change in leverage from the old pedal and moving it down an inch or so, and also getting the pushrod correct length on the piece that pushes into the master cylinder. So I have done my research, and don't think I am asking the same question.
I have a 66 C20 that had power non-disc brakes up front and non-disc in the rear. I swapped the entire front crossmember from a '79 C20 and the non-disc 14 bolt from the same truck. Bought a new master cylinder and installed it onto the existing booster (which is pretty new and worked fine prior to the crossmember and associated disc brake swap). I have pressure bled the brakes and used my assistant (aka daughter) to do the two person method. No more air, I am quite confident. Did pretty meticulous work to get the pushrod that engages the master cylinder to the correct depth. I really don't think I need to move the pushrod on the brake pedal any lower, since I am using the same brake booster, only changed the master cylinder.
The brakes are soft and not very effective. Wanted to take out on the road for the first time in over a year, but didn't dare go over about 20 MPH. I did take it around the neighborhood, and it was awesome.
Can this be as simple a fix as lengthening the pushrod on the brake pedal? Gonna go try that, but does anyone have any other thoughts? Please read the above, I know it is long, but I have paid attention to the usual suspects already.

[64chevmn]

Does your brake pedal go all the way to the floor when you are heavily applying the brakes?? If you have a solid pedal and it is not bottoming out on the floor board, I think the push rod should be fine along as it is pushing straight in and not at a serious angle. With the brake pedal in the resting position, you want the push rod to have very slight contact with the booster/master cylinder so when you start pushing the pedal down you have instant pressure being applied to the master cylinder.

[earl84]

Pedal is soft, AND goes to the floor. I am going to extend the master cylinder pushrod a little and also the brake pedal pushrod a little.
Is a soft pedal only related to air in the system? I suppose its possible there is still air. When using the pressure bleeder, it didn't push as well as it has in the past, and it was amazing how well it worked then compared to now.
I'm sure I'll figure this out, there are only so many things it can be, just dying to actually drive this past 20 MPH in the neighborhood, and see how the 454 moves this thing down the road.

[Sharps40]

Pedal soft and goes to the floor = air in the system. Bench bleed master, purge lines/cylinders, adjust shoes.

[PGSigns]

First thing I would do is check the adjustment on the rear shoes and the next thing is ensure the master cylinder has the correct bore. The one you need should have an 1 1/4 bore for the big volume you need with the brakes you have. If the one you have has a smaller bore you will run out of pedal and have soft brakes. Not enough volume to work the system.
Jimmy

[64shortbox]

I had the exact same problem when I changed over from manual drum brakes to power discs. I had my wife pumping the pedal while I bled. That didn't work. I tried the gravity bleed trick - opening the bleeders overnight with a full master reservoir. That didn't work. I tried jacking up the front end as high as I could get with the bleeders open overnight then the same at the rear end and that didn't work.
I finally made myself a home pressure bleeder system and that worked. Pictures attached. I actually had to increase air pressure to 25 PSI to get all the air to bleed out of my system. Also did you center the proportioning valve and lock it centered before you started to bleed the brakes? If you are running a factory proportioning (combination valve) unscrew the plastic switch at the top of it (the switch that the brown wire goes to that trips the BRAKE light on the newer cars & trucks. Reach down with a small flat blade screwdriver and center the valve - once you see it you will know what I'm talking about. They make a little tool that screws in place of the switch to hold that toggle centered. It's plastic and runs about $10.00 on eBay. That's where I got mine. Since you are running Disc/Disc you might not have a proportioning valve - I don't know about Disc/Disc brake systems.
If you have a trusted place that can pressure bleed the brakes I'm sure if you took it to them and had them pressure bled your problems would be over.
Clear as mud? If you have any questions please ask.

[earl84]

Problem solved! Feel kinda silly actually.
Anyway, figured I would start with the easiest and adjust the rear brake shoes, even though I was sure I had done that when I replaced just about everything on the 14 bolt before sliding it in to replace the HO52. Guess what? Not even close to being adjusted correctly. Did the adjustment, had a hard brake pedal. Life is good!
Took it out on the highway, checked fluid levels, checked leaks (NONE!) and came back and took my daughter out for a quick ride, even let her drive. Good oil pressure, doesn't get hot, battery is charging, everything appears to be working right. First time on the road in well over a year
Now on other things since all the mechanicals are working properly for now (well, actually the Qjet choke isn't working quite right).

Want to thank everyone for their assistance with this. Love this forum.