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

test

Dump question but did you adjust the rears up until they scraped a little?

I did indeed...

I am befuddled.

Of note, through all of this I've replaced both rear wheel cylinders (one defective, and one because I needed a later style one to go with my AL master cylinder (bran new for an 89 Diplomat) and the RF caliper after I broke the bleeder screw off.

I've pumped probably 2 gallons of fluid through the system when bleeding and after the 2nd to the last bleed, I got some nasty fluid out. On the last bleed, the fluid was foggy, but not as bad as the previous bleed.

Could that caliper be hanging up some how?

put a block of wood under the pedal to limit its travel to the normal height (anytime, when checking or bleeding). clarify about the pedal stopping halfway down (which it would do if the brakes were functioning normally), more details please

Gotcha on the block of wood.

The pedal is stopping halfway down (which indicates normal operation) however no matter how hard I stand on the pedal, no lockup and longer stopping distance. The initial bite is as it should be. The car stops just fine in traffic situations, but when jumping on the pedal at ~30 MPH, nothing locks up and the car comes to a stop with no drama, albeit in much more distance than it should.

Pedal doesn't not pump up

Pedal "bottoms out"(better description than "stops halfway down") in all braking situations

Adj prop valve fully open (full flow to rear)

I've got to think there is more air in there, but I've bled bled bled and pumping the pedal doesn't change the system behavior.

this is power discs/drums right? (1) recheck the round pushrod nub clearance (2) take the line off of the MC front port (for the rear brakes) & cap the MC with the brass inverted flare male plug fitting & drive it & see how it acts with us isolating the front discs

Will do.

I also had one of the MC-Prop valve coiled lines with one coil above the MC. Rectified that and will bleed, test and recheck the pushrod clearance before isolating the front.

Might not get the opportunity until Monday though.

Allright, so here is the latest.

1st, I have NOT yet isolated the front brake channel and tested.

What I have done is re-bleed the brakes (using a 2.4 under the pedal) after re-routing both MC-prop valve lines such that all of the coils are below the level of the MC mounting. I also visually verified brake operation at all four corners.

The result is a HARD pedal that feels as it should, and normal braking is as it should be. That said, no matter how hard I stand on it at any speed, not even the rears lock up and it gently slows to a stop after a much longer distance than it should. The pedal does not pump up, and braking begins immediately upon pushing the pedal.

Could this symptom be caused by an MC mismatch? I replaced the stock replacement (Big A Auto no less!) MC with a KH unit from Rock Auto listed for an 89 Diplomat. It is listed as having the desired bore. Several aftermarket brake manufacturers list "Master cylinder bore size too small for the system volume requirements." in their troubleshooting guide for "Poor Brake Pedal" but the symptom is no more specific than that.

I had that real drawn out stopping distance once & it was a partly crimped front line (before the splitter so both fronts affected) on the stock car but people have reported that too large of MC bore dia will give an inodinately hard pedal to the point of literally having their a$$ up in the air stomping on the pedal to generate any force but that ain't been my exp with the 1&1/8 MC I used on my 65 dart (& I ain't that strong). what Bore is yours? I gotta lean toward a partial blockage of some sort & I would go ahead & isolate the halves again for a start

I'll double check the lines and isolate, I did re-flare 4 lines and the 3/32 jaw in the bar was a bit worn, so caused some frustration.

On the MC, it is a 1 1/32" (got sucked in by the price, $17.59). One wouldn't think 3/32" would make that big a difference, and wouldn't the line pressure be higher with the smaller bore? Could it be a matter of fluid volume? Could the stroke be less on the 1/32" MC?

Rear brake performance can be affected by wheel cylinder size as well.

Larger bore rear wheel cylinders put more force on the shoes than smaller bore.

You all may be focusing on the wrong end of the braking system.

The rear cylinders are new stock replacements. I considered doing the Ehrenberg small wheel cylinder trick, but as my Prop valve was hosed, I went with a Wilwood integrated distribution/prop valve, so stayed with stock replacements for the wheel cylinders.

At this point, it doesn't seem to be getting enough pressure to the front or rear. I am unable to get even the rears to lock with the prop valve wide open.

Stock for what though?

Cause you say this



And it's confusing.

Heck, that confused me on the re-read.

>> In the mid-1970s, Chrysler eliminated the rear brake residual pressure valve from the master cylinder. Its function was to prevent any air from sneaking into the system via the rear wheel cylinder cups. In its place, Chrysler substituted "expanders" in the rear wheel cylinders. (Expanders are dish-shaped steel inserts that exert outward pressure on the cups.) If you should decide to use a master cylinder from a 1975-up car, be sure you have the expanders in your rear wheel cylinders. For at least 20 years they have been universal in all replacement wheel cylinders and rebuild kits.

Lest I introduce more confusion, the car is a factory power brake, disk brake car. I'm not converting to disks per this article or anything like that.


The replacements are O'Riley house brand new cylinders for my car (73 Barracuda).

So, you have a mostly stock 73 Cuda disc brake car with a late model M/C?

I did that when I converted my 65 Cuda to discs, Mushy pedal no matter what so I just went with a 4 bolt disc M/C.

Yes, stock but for the MC and aftermarket combo valve.

Lines inspected, no kinks or reduced line diameter anywhere where I monkeyed with them. I did not chase all the lines to the end of their route however.

Rear channel isolated, noticeably reduced braking performance, but still unable to lock the fronts. De-isolated the rear channel, bled and back to the former situation.

The 3/32" smaller than stock bore diameter is all I can think of that *may* cause this symptom at this point. This will teach me to cheap out. Anyone need a new 1 1/32 MC? I may have one available

Any other thoughts on troubleshooting avenues guys, before I part with more cash?

PS, I just noticed I failed to cite the Ehrenberg Disk-O-Tech article a couple of posts back. I poached that text right from the MA website.

I still think not enough psi is reaching the corners. I also dont think the 1&1/32 bore is a problem. a 2000 psi gauge hooked to the corners would ans that (I have one & it was cheap). you know what I would do, just me I would run some parts house prefabbed 3/16 line from the MC port next to the firewall to a brass inverted flare "T" then run both outlets to the front discs (with the other MC port capped). with it bled out if it wont lock em it'd have to be the calipers (one or both) or the MC. those lines are pretty reasonable as are the fittings & you have been comfortable with the fabbing you have done so far in diagnosing this

way back when i had a older (70's) winnabago motorhome come into my shop with back brakes completely burnt up,even cracked one drum,someone had replaced the master cyl about 300 miles back down the road,i replaced everything on the rear brakes,took it for a drive and it wouldnt stop well just slow down no matter how hard you pushed on the petal,after some head scratching i decided it had the wrong (to small) master on it)put the correct master on it for a 400 series truck and that fixed it,however the problem started when the owner left the other shop he forgot to release the parking brake,and drove it that way for around 300 miles without knowing it
hope this helps some
a true story!!

So a buddy/co-worker of mine moonlights at an Advance Parts that is attached to a warehouse. He arrived this AM with a 1 1/8" MC listed for an 89 D150 (a CarQuest one, no less and not their house brand, fruit of a merger). $27 and he'll take it back for me if it doesn't fix my problem.

Looks like I'm going Air Force Method for this step (throw parts at it until it works).

If this works, YAY! If not, I'll pick up a pressure gauge and continue in a diagnostic fashion.

I'll report back, and thanks for you input thus far everyone.

Chris

Update:

After the 1st MC being a dud, my buddy had his store deliver one that hadn't been opened and I swapped it out, setting the pushrod clearance and bench bleeding on the car. He also sent a loaner brake pressure gauge kit.

What I noticed, 1, the 1 1/32" cylinder is noticeably smaller in diameter and 2, the 1 1/8" cylinder holds roughly 1/2 again as much fluid and has a longer stroke. When I was complaining about the pedal only going half way down, it was the cylinder. It now goes to the same point it always has.

After bleeding the system yet again, way better initial bite and much more speed scrubbed off before the pedal bottomed out. I used the brake pressure gauge at all four corners and at each corner, the pressure spiked, then bled off as the pedal went to the stop.

On a hunch, I grabbed the flex line on the RF while wife helper pushed the pedal, the line swelled up in the middle like a snake that ate a rat. The LF and rear flex lines swelled as well, though not as dramatically. I have encountered this on other cars, but never on flex lines that "looked ok" on a cleaning and static visual inspection.

I think I found the problem. I've ordered up some flex lines, and I can't imagine they will not fix the problem.

I've had this car (3rd owner) since 1988, and it has done a lot of sitting (he fluid that I initially flushed was cloudy brown and full of little black chunks). That said, I've put about 80K on it over the years as it was my daily driver until 96. To my knowledge, only the shoes/pads have been changed until this summer when it got 2 wheel cylinders and one caliper, as well as an MC (the one I think is original puked out the rear and ruined the paint on the lower part of the booster) and the prop valve, which has given me fits since the Clinton administration. All of this started because I had to pump the pedal when braking and had no rear brakes.

I shall report back after the install and One More Bleed. I need to buy stock in Prestone.

(3) brake hoses were doing that, that is unbelieveable & could of been catastrophic. that sure explains where the psi was going!

No doubt! Particularly on the RF hose. They all look normal when not under pressure. I guess it is a testament to materials and engineering. I'm curious to see what they feel like when pinched with no fluid in them.

And, of course if I had followed THE axiom from my A&P days (always troubleshoot the likeliest failpoint 1st, I may have been done with this project weeks ago

I think the wife has earned (herself) a paid vacation (the grand canyon would be close)

She sure does! Thinking Albuquerque for the Baloon Fest next weekend.

Well, lines installed and the brakes worked great for about 50 miles, then then it started pulling hard the right. The sole unreplaced hydraulic part, the driver's side caliper, started leaking. Another $25 for an O'Rieley rebuilt. I checked the rotor thickness and runout and it was good, so put some new pads on as well.

Should be great, right? On the test drive the booster gave it up and can't stand on it hard enough. I'm sure it was going all along, as at some indeterminate time in the last few years while the car was sitting, the rear seal puled out in the old 4 bolt MC and there was fluid dripping from it for a while. I should have approached this as a brake system overhaul and I would be a lot of time ahead!

I got a rebuilt O'Rieley booster yesterday afternoon and the paint is currently curing. Hopefully, I'll get it installed this afternoon.

Unbelieveable, Mr Murphy just ain't gonna let you go on this deal. I think I'd rather be up in that balloon than with those brakes (& I'm scared of heights!). In spite of the RF leak, if it is pulling to the right there there is a problem with the left side (it ain't doing its job).

Booster installed! It is still quite tight (high effort), but loosening up nicely. No pull or drama of any sort. I still have not dialed in the adjustable proportioning on the rear circuit though.

The LF caliper was the one leaking and causing the pull, so good there!

Thanks guys for all your assistance here, despite the final outcome of the project, it was most valuable and I've learned a lot.

One questions, so I still have the 1 1/8" MC on there. I still have (can't return) the 1 1/32" MC. It has a smaller casting, and from bleeding, I recall it has a shorter stroke from bleeding 87 or so times. Clearly a smaller volume of fluid displacement as well.

Any idea what going to the 1 1/32" would do for the pedal? Ideally, I would like a shorter stroke and lighter pedal effort (though without my new booster broken in, I don't know what it will be with my current setup). I think it would increase pressure, reducing the effort, and maybe have the shorter stroke.

Thanks again
Chris

I ain't did much MC swapping but general theory says going back to the 1&1/32" from the 1&1/8" would give (1) an easier pedal & (2) a longer stroke. I'm sure you're looking forward to swapping it & doing some more bleeding! Make sure the booster round nub clearance is correct

I am reading this diligently as I have 70 bronco with all wheel drums and now have a pull to the left. No leak showing and flex lines replaced.

I had a similar issue you did on my 67 Vette. Manual 4 wheel disc. I replaced all flex lines with braided lines and the pedal got much firmer than when all stock rubber lines were good..

check lining adjustment on the pass sides & if all good then open em up for a visual. EDIT probably wouldn't hurt to check/equalize the adjustments on all 4 corners

Thanks Robert. It has self adjuster star wheels. So get under there and turn until they hang up a little? I will start my own thread once I get going as I don't have the tool or knowledge yet to pull hubs.

get it up on stands on all 4 corners and spin the front wheels forward by hand & spoon it till at one point in the tires' revolution you can hear a slight "tick". On the rears idle it in gear in drive (wheels spinning) & have a helper hit the brakes to stop the wheels & you go a bit tighter then he lets go & repeat till you hear that same "tick". do both sides and safety first of course. if the shoes etc have been replaced/R&R'd & anything in there undone its a good idea to spoon em up till locked solid then go backwards which takes any possible slack out of the parts & that is alot of extra work working with the adjuster which is always a pain but I think you will be OK as is (without that step)

Thanks. It's a 3 speed so I will do the rears like the fronts since going backwards repeatedly is not cutting it.

To the op, is your car locking them up now?

What is spoon mean?

http://www.ebay.com/itm/like/231266122889?lpid=82&chn=ps&ul_noapp=true

One of those special drum tools..

P d'ro, I haven't had opportunity to test/dial in the prop valve yet, so unknown. That said, I can't imagine they won't. I just haven't been able to get to someplace appropriate to do the deed as of yet.

Yeah, I might leave that for when I'm bored or something, or try it next time I have to open the system. I'm going to do the C-barge rotor upgrade when my rotors give it up. They're both scored pretty good, but width and runout are in spec. I imagine I'll crack one in the next year or so, now that its all road worthy. I have tried to hasten the situation by swapping out the organic pads for semi-metalics.

Hey guys, final report on this debacle. Success!!

Some details, I think the O'Rielly Auto re-manufactured booster is weak. It helped to a large degree, but with the 1 1/8" MC installed, I could barely achieve rear lockup and the prop valve had to be set to max braking and I had really be standing on it.

I installed the 1 1/32" MC and low and behold, better braking than I've ever had in this car (I've had it since 1988). I got the prop valve dialed in from 30 MPH, which I could do on the weekend in a mostly empty stretch in a commercial area. Wasn't comfortable doing 50-0 braking on the block for safety reasons. The homeless folks hanging out in the yard the Rescue Mission cheered for me though. I'll get high speed braking dialed in when I get a chance to go to a buddy's house who has a long flat access road as the back way in to his neighborhood.

Once again, thanks RapidRobert and everyone else who helped me out here. I'm going to call this project good!

Chris

Better way to adjust your brakes is to tighten up your star adjusters all the way tight and then back off.. Seems to set the brakes into the drum better..
If you count the clicks, as you back off, you can do the same with the other side....

Will this raise the brake pedal at all?

with everything spooned up high and tight it would allow less pedal travel to actuate the brakes but for a higher at rest pedal (which I think is what you are asking), it would take an adjustable pushrod (manual brakes) or custom fabbing a longer rod if power brakes to raise the pedal