Hey guys and girls, referencing the subject...
Car is a 73 Barracuda with stock 10x2.5 drums on the rear.

Symptoms:
Spongy pedal (requires pumping, can't lock F or R brakes)
Clunk from LR on application and release of brakes
Slight fluid leak from both rear cylinders (driver's side cylinder replaced)

I replaced the LR wheel cylinder as pretty much the 1st step in troubleshooting when I discovered that the rear shoe had not returned properly and was outside of the e-brake expander. I un F'ed that, replaced the wheel cylinder, reassembled and adjusted per the manual. All appears in working order on both sides. E-brake works, though the cable is massively stretched.

Will the collective Moparts brain trust get me on track here? Thoughts on where to start?

While I haven't measured the drums, they do not appear out of round and the braking surfaces are in good shape. Pads appear in good order as well. MC pushrod clearance set to .020" using a depth gauge.

Relating to the combination valve, can those things leak internally?

Chris

first replace the leaks which I believe you have done then a visual to see if everything looks copacetic on all 4 corners (everything assembled correct/no damage) then spoon up the shoes then bleed the MC then bleed the corners. EDIT gotta find out what that "clunk" is

Thanks Rapid,

I have procured an detailed photo instead of the exploded view diagram I have, and am going to pull the drums and verify everything is connected/routed properly and double check the leaks. Hopefully, that will reveal the clunk.

The leaks as I observe them with the car on the ground now are likely residual fluid from the extensive bleeding efforts I have undertaken.

Thinking about it, I'll get a hardware kit and pull the whole thing apart and clean everything up.

It seems like an internal leak as well to me though. The MC is a bran-new KH (under warranty - doesn't mean it isn't bad), bench bled before installation. I flushed the fluid in the whole system and bled it with a mightyvac. Can the combination valve recirculate fluid?

the 2 halves (front discs or drums and rear drums are still hydraulically seperated even with a combo valve which likely includes a metering valve and a proportioning valve (I forget their exact functioning). I'd "keep it simple sam" & find/fix the clunk & confirm no leaks/spoon em up then bleed the MC then the corners

could the "clunks" be the shoes jumping around on the shoe contact pads on the backing plates having divots on them ? does there appear to be any pulling effect coming from either of the rear brakes ?

Well, I pulled the rear wheels off and inspected everything against a detailed photo. The lower retract spring on the driver's side had either not been properly attached or had somehow come loose. I put a hardware kit in both drums and all the springs I pulled off were noticeably wimpier than the new ones, clunk eliminated.

On to bleeding. Re-bled the master in place using the brake pedal. No fluid drop. Bled the RR with the mighty vac and sealed it. Attached mighty vac to the LR and could get no fluid. left the catch can hooked up and used the pedal, appeared to work. Went back to the RR, opened the bleeder, attached the catch can and gave it a couple of pumps, repeat once again for the LR. On to the front, the pedal goes to the floor both sides, properly bled.

So, the pedal would only go halfway down on the rears, and with the whole system sealed, the pedal only goes halfway down. I am befuddled. I think it either has to be a partial blockage in the rear channel or that 2yr only combo valve that I had replaced some of the seals in years ago. At any rate the situation is a bit improved, but more work required.

Any ideas here regarding the valve/blockage?

what I would do is get some brass male inverted flare plugs & cap the MC ports & if the MC is bled out and it is holding pressure the pedal will be rock hard with virtually no travel (eng idling-these are PB correct?). the fittings are 9/16-20 and 1/2-20 & your parts house would have em in the "Edelman" fittings cabinet. then onto the prop valve & I would unscrew the rear brake(s) "out" line & cap the prop valve female open port with a 3/8-24 similar male brass fitting & work on the fronts & see if you can get them bled out and have the same high and tight pedal that you have with the MC capped. that'd be a good start. I would put a block of wood under the pedal so it dont go to the floor but stays pretty close to its normal range of travel. holler back when you can

Got it, isolate and take it from there. Will report back

If you are still having trouble, post a photo of the problem side.
Also if the RR is getting fluid pressure and not the LR, both rears are fed from the T on the axle housing at the same time, any blockage would be from the t to the wheel cylinder.
If nothing visual, loosen the problem side from the T and try to get pressure there, work your way to the wheel cylinder.

Will do on the photo. They both got limited pressure from the pedal, but I was unable to use the mightyvac to bleed the LR, worked for the RR though. I'll check the T as well.

THanks

OK, Isolated the master - Good
Blocked rear output at the combo valve - 1\2 pedal
Rear hard lines, flex line and y-block - clean and clear

I pulled the combo valve, disassembled it as much as possible, cleaned and soaked with penetrating oil. I then used a small screwdriver to move the shuttle valve, but was unable to move it back non-destructively (even with compressed air). It looked like it was stuck open, so there would be flow to the rear. I thoroughly cleaned and reassembled the valve, installed it and bled the brakes. No more air, the pedal is rock hard, but only goes down half way. I'm thinking it is hydraulic lock in the combo valve. The slider must be disadvantageously stuck and when the valve opens the rear channel, no flow.

Any other ideas or avenues to explore? I'm almost ready to get one of those Wilwood adjustable combo valves and plumb it in...

blocked off the MC & was high and tight & rehooked things up and capped output to rear & pedal goes down 1/2 way? does the travel seem excessive or OK? does it pump up?

No pump up, not enough travel. Pedal is high and tight though, just feels like it has a stop about 1\2 way down.

I just finished a couple of tests. First I put the rear up on stands and had my wifehelper hold the pedal down with the engine running. I could spin both rears.

Next, I installed an MC bench bleeder on the rear channel(front MC output) with the tube in the MC, started and the pedal feels as it should. Standing on it, the pedal goes down maybe 2/3 of travel and feels like pads on a rotor. No hard stop.

see if I am reading this right, you unhooked the forward (closest to radiator) line in the MC (for rear brakes) & hooked the short bleeder line to it (the MC port) & run it back into the MC bowl (just like you are bench bleeding (that half) of the MC) & the system felt "normal" as far as the front pads engageing? If all good on that & the other half (for rear brakes) of the MC is bled out then there has to be a blockage from that half rearward as you said. if we're thinking the prop valve is fubared I'd almost wanna go back to your parts house & get a short length of prefabbed 3/16 brake line with the male inverted flare ends and a double female inverted flare union and a 3/8-24 male inverted flare plug to cap the hole in the prop valve that the rear line was in that you took out, to bypass it COMPLETELY & see if the prob is there or further downstream. it'd be some work but that is my 2 cents worth at the moment

I actually picked everything up to put in a combo valve, including the union and prefabbed line you discuss, and I happen to have a plug. I'll try this before I get to work splicing the Wilwood combo valve in. Luckily I resisted the temptation to open the pretty, shiny part before I was fully satisfied that the combo valve is the issue.

I'll give it a shot and report back.

yeah on a toughie if the MC (& booster if PB) is high and tight when capped then we wanna move outward downstream till we find the issue

OK, so I bypassed the prop valve completely on the rear channel as you suggested Rapid, and the rears work!

I've replaced the flare nuts going to and from the new valve and rough-routed the lines, but haven't mocked up a mounting or done a final line fitting yet.

Thanks for getting me going in the right direction!

anytime bro, can the prop valve be dissassembled to see what is stuck. might be an easy fix. then you can sell the wilwood valve plus no brake line fabbing would be needed for the wilwood

Got my project interrupted by a little vacation!

On the factory prop valve, on more than one occasion I have removed, disassembled, cleaned and reassembled it. It is one of the oddball 73-74 B&E body valves, as far as I know. No reman available. Problem is, it is iron and the little brass flare disks can not be removed non-destructively, at least without proper tooling.

This time, I was unable to free up the shuttle which is contained by the flare disks. Previously, I pushed it to one end of its travel with a small screwdriver and soaked the inside with penetrating oil. I would then be able to push the valve back with a piece of coat hanger through the flare disk. Repeating this process three or four times would get it moving again. Not this time though, I got it stuck at one end and couldn't push it back with a hanger. I left it soaking in penetrating oil for a couple of days, same deal. Couldn't even move it with compressed air.

I've finally got the Wilwood spliced in (and am going to purchase a 3/16 flaring tool instead of the bar for lines on the car in future) and am now on to the bleed. Good times!

WIll report back.

All up and running! Brakes seem to work great but... when I was attempting to dial in the adjustable prop valve, I'm unable to make the brakes lock up. I did get one chirp from the RR, but otherwise it just comes to a stop without drama. I tried several times. I've bled and bled the system, starting with a mighty vac and going back to the old fashioned way.

Strange though, the pedal goes to the floor when bleeding, but seems to stop part way down with the bleeder screws closed, feels like there is a physical stop.

I'm thinking I need to do another round of bleeding, but any ideas on the pedal behavior?

Thanks