no brake pedal what am i doing wrong?

[683/4farm]

68 3/4 ton gmc just did disc brake swap from 84 all new suspension parts,calipers,hoses,master with original booster that is holding great vacuum,new rear shoes,springs and cylinders,no air in the lines and im still getting no pedal,goes right to the floor,i dont know what im missing or doing wrong and hopefully someone can chime in please and thank you in advance.

[dwcsr]

Three things that you should look at
Was the master cylinder bench bleed? if not take it off at do it.
Is the Prop valve centered and was it centered and bleed using the prop tool.
Are the rears adjusted up properly

If these tree things are not done it will never bleed properly
you either have air trapped in the master ( bench Bleed it) or the prop valve has shifted and closed off the front or rear system( it should do this if its working) so you need to manually hold it in the center with the tool. The rear shoes not being adjusted contributes to bleeding issues.

[683/4farm]

The rears werent touched since before i did the disc swap so should still be adjusted from last summer,i did bench bleed,and prop valve ive heard of this recentering but dont see anywhere to do anything,only things i see on it are the electrical pin and the four holes for lines

[683/4farm]

I should also mention the proportioning valve is the one that th po had installed with the 71 c20 master booster before the swap,i didnt have the one from the 84 that everything else came from

[sprint_9]

Is the proportioning valve a disc/drum valve?

[683/4farm]

No idea how can you tell?

[Ta12sec]

Have you verified that the brake pedal actually pushes the master cylinder, I saw a swapped truck that had no brakes because the pushrods was too short and truck had no pedal.

[683/4farm]

it is pushing the fluid through the master

[683/4farm]

I had thought of that also so I pumped and watched the reservoir

[old Chevy guy]

Sounds stupid but make sure the calipers are on the right sides. It's not hard to do ,if you put them on the wrong side the bleeders are down instead of up and you can't bleed the air out. Sometimes it's just the simple things that trip you up. If the prop valve came from a 71 you should be good. Is it hanging just below the master with the wire connection up? I'll try and post a picture of mine in a few minutes.

[old Chevy guy]

Try screwing out the part under where the wire is plugged in

[683/4farm]

Im assuming from 71 but my wire connection comes from the bottom,has the two lines coming from the top going to the master and teo lines comint from the bottom,looks nothing like the one you have there

[683/4farm]

And they are on the correct side bleeders up

[683/4farm]

Here is mine I there right now

[frankslagoon]

I'm not an expert on this disc swap , so I won't try to explain what I don't totally understand, but the old drum drum set up blk valve is only there to shut off one side if there's a failure. The disc blk. does this also but it also feeds the frts. more fluid or pressure. The disc drum won't work correctly or at all with the old blk. looks like your using the drum/drum blk.

[683/4farm]

That would be great,i may try to pick one up this week if this is the case

[old Chevy guy]

I'm no expert either but I agree that does not look like the right proportion valve for the disk setup. Probably at least part of the problem. Start there and see what happens.

[Stocker]

I agree, that looks like a distribution block (drum/drum), not a proportioning valve (disc/drum). And it appears to be upside-down; I have only seen them with the wire on top. Not sure if that matters but why take the chance.....

[683/4farm]

Good to know

[Ta12sec]

The wrong valve may cause poor braking or locking up but shouldn't cause no pedal, the pedal feel is only related to an airless system, if you are sure the master is getting pushed, you have air in the lines.