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Discussion Starter #1
Hello all. I need some of your expert advice.

I have a 72 4 door Nova with a 307 and TH350. It came originally with a dual master non powered 4 wheel drums.

All brake components were in terrible shape.

I replaced everything with a Right Stuff Detailing front disc power brakes conversation kit. I also replaced all the lines and completely rebuilt the rear drums.

This is what I did.

the booster was installed and I set the clevis on the petal on the lower hole. I set the petal with 1/8 of play before engaging as instructed.

I used a measuring tool to set the booster to master rod length with 1/16 of play.

I bled the master properly.

I used the key that goes in place of the brake switch in the combination valve to keep the shuttle centered. I bleed all 4 sides in the proper order.

The shoes are in the correct locations. Larger to the rear, small to the front. I set the drums to slightly drag.

the problem is that with the pedal fully pressed, the rears engage, but I can turn them by hand. With the car in the air, rear tires off, drums secured with lug nuts, and the trans in gear (forward or reverse), I can get the rear drums to slow all the way down by pressing the brake hard but they still spin very slow.

I don’t know what else to check.

the rubber Brake hose from the body to the rear axle Is brand new. The combination valve is centered. I bled everything 3 times. The pedal seems a little soft the first inch then grabs hard.

last thing, the emergency brake does the same thing and the hydraulic brakes. With the E brake all the way in, the drums still spin very slow.

any ideas would be appreciated.

thank you in advance
 

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just a thought here ....................... could be that your rear drums ARE OUT to the 'max diameter' ...........

in other words ........... your rear drums (could be) / are worn - out ............... your rear brake shoes only 'expand so far' , then , that's not enough to completely . . engage your rear drums .
example : your rear wheel cyl only push your rear shoes , so far . I might check (or have u'r) rear drums
" " max diameter " " ..... checked ..... that dia. is / should be marked on each drum (usually along the 'outside edge' ) on each brake drum . . . (or any 'rotor' ) .
Your rear "still turning , when in gear " . . . . (hard too tell , with-out being there) . . . . could be "cable adjustment" ? . . . . . are the same thing = rear drums just worn too much .

just . . . . some idea's . . . . keep us posted .

jim
 

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Discussion Starter #3
Thanks Jim. Drums are brand new. Shoes, wheel cylinders, all springs and components, rear rubber line, steel line, combination valve, master, and booster all new.

the top half is a front drum to disc conversion kit.

what do you guy think about me maybe having been given the wrong combination valve or wrong master or even a bad master?
 

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10 - 4 . . . . . (I couldn't see that from here , lol ) . But, good too know . . . . . (new rear drums) .

OK ...... I did my 'front disc' brake up-grade (a few years back) ............ I had all new parts (well, rebuilt
brake booster . . . and, I rebuilt my front 'Delco' calipers (than, getting 'China parts' ) .
Also, I bought a new "combination valve" (from InLine Tube) ........... (to replace my old - 50 year -
junction-block & stock 'metering valve' ) . . . . on my 69 .
They (Inline Tube) , sent me (what I thought) was, the Wrong combination valve & S/S lines (to my m/c
..... and mounting bracket) .
So, I called them ............. then, sent them a picture ........... They then told me - OK - ............ but, also
said that they ALL used the same combination valve ( I took that to mean ; that the combo valve - fit all
models ........ just the "bent m/c lines & brackets " were different - between different makes ) .
( ....... they did sent out the correct parts ....... ) .

With that being said - - - - too me , would mean - - - - "All of their combination valves , work the same" ..................... and, you can't have the " " wrong " " combo valve .
He even said , just different 'brackets and m/c lines ; for different models' .

hey .............. if that's true ............. just , says = your combination valve should work (as for being
the "correct valve" (just sharing what I was told) .
having a "faulty valve" . . . . I don't know . . . . (does that make 'sense' ) .

Maybe , then consider something "else - in th' loop"

just trying too help - out ............. later , jim

 

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Discussion Starter #5
Thanks for the help Jim. I appreciate it.

this is my set up...

411078
7A91998C-6670-462C-A9D5-E31033F247AB.jpeg

411079
 

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I think they are just out of adjustment. Has it been driven since all that new work. Set the rear adjusters till you get a slight drag and let the rear automatic adjusters do their work by going in reverse a few times and quickly applying the brakes. I did the exact upgrade you did 100% new brake system. I'm not road ready yet but my rears are doing the same due to lack of adjustment. What sucks on my rears is it does not have the knockouts allowing me to adjust with the wheel mounted. I just tightened them up just enough so I could slide the drum on.
 

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Discussion Starter #7
Same here with everything you said. Not road ready. The car is up on jack stands. Waiting on front sway bar and front upper control arms. Rear end 10 bolt had just been rebuilt with 3.73’s a Detroit Trutrac, and Moser axles just prior to this brake upgrade.

I don’t have the star wheel access ports or even the knock outs. I adjusted them to where they were very tight where I could barely turn them. Hit the E brake to center things, then back off about 8 clicks. Now there is a light drag on the drums. I can spin the tire just under one spin with moderate force. I think I have them adjusted pretty well.

I’m worried the master is bad. It makes a low pitched howling sound when I press the pedal. The pedal is a little soft the first inch then gets real hard. The reads don’t even engage until The pedal reaches that hard point.
 

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Your master cylinder and associated parts are beautiful. You are doing nice work. The backing plates can be drilled to allow access to the adjustment wheels. The drill holes can then be filled with rubber grommets. I suggest you check the tension on the emergency brake cable as it is independent of the hydraulics. When you get the emergency brake working, bleed the system some more. The master cylinder is the best place to start, just to be sure. Then onto the lines. A pressure bleeder can eliminate the problems possible in other methods. If after re-bleeding everything, and the problem remains, go for another master cylinder. Stick with it. You will get her done
 

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Sounds like you have them adjusted then. How funny I did the exact rear end rebuild gears and all should have the drive shaft in a few days.
 

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Does your master cylinder have a residual pressure valve in the rear port?
If you pump the pedal does it firm up, and does it stop the rear wheels from rotating..!
 

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Discussion Starter #11
Your master cylinder and associated parts are beautiful. You are doing nice work. The backing plates can be drilled to allow access to the adjustment wheels. The drill holes can then be filled with rubber grommets. I suggest you check the tension on the emergency brake cable as it is independent of the hydraulics. When you get the emergency brake working, bleed the system some more. The master cylinder is the best place to start, just to be sure. Then onto the lines. A pressure bleeder can eliminate the problems possible in other methods. If after re-bleeding everything, and the problem remains, go for another master cylinder. Stick with it. You will get her done
Thanks man. Great idea about drilling out the backing plates and pressure bleeder.

Thanks for the advice about the emergency brake. I checked it again and the E brake also has trouble stopping the wheels. I have to push the E brake pedal hard as far as it can go just to slow the back drums to a stop. This is in the air in jacks with the tires off and drums on with a few lug nuts in drive. I can’t tell if it’s the master or the rear brakes. FYI both rear brakes act exactly the same. They work, but are very weak.
 

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Discussion Starter #12
Sounds like you have them adjusted then. How funny I did the exact rear end rebuild gears and all should have the drive shaft in a few days.
Sounds great Mark. I just hope I get these brakes working.
 

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Discussion Starter #13
Does your master cylinder have a residual pressure valve in the rear port?
If you pump the pedal does it firm up, and does it stop the rear wheels from rotating..!
I not sure, but pumping the brakes doesn’t change anything. I can’t get the wheels (drums) to stop rotating no matter how hard I press the pedal. I can only get them to turn very slowly.
 

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Discussion Starter #14 (Edited)
Where should this residual valve be?
From what I understand the combination valve in this kit is specifically designed for a disc/drum combo with the required three components all in one. Metering valve, proportioning valve, and pressure differential switch all built in. I’m not sure if a residual valve is another name for the proportioning valve the is located in the rear of the combination valve in line with the rear brakes. Unless they accidentally sent me a disc/disc combination valve that doesn’t have that part for the rear brakes.
 

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Discussion Starter #15
I always though a residual valve was for hot rods with the master cylinder mounted under the floor board real low.
 

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May or may not be material, but remember that brake shoes aren't arc-ed anymore (don't know how to spell that). Brake shops used to put shoes on a machine that would grind the friction material to the exact same radius of your brake drum. That process is actually illegal in some states and isn't done anymore. What they commonly do now is grind the surface of any new shoe you get to a slightly wavy pattern so that, when you first drive the car after a brake job, the slight peaks wear first and the shoes 'self arc'. Doesn't quite work as well as arcing, Either way, you'll have more shoe to drum contact as the shoes wear into the drum (especially if the drum has been turned),
 

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Discussion Starter #17
Thats great info. I hope that is the case. I re bled the master on the bench and re bled the entire system again paying close attention to the rears. Still the same.

cut up in the air on jacks, now wheels, drums on held on by lug nuts, and same thing.

In drive, I can get them to stop if I hold the pedal down with both feet as hard as I can. Then they start creeping slowly around. This is frustrating.

also, I think I forgot to mention that with the engine off (no booster) the first inch of pedal travel feels soft, then very hard after that where it should be. The rears don’t even engage during that first inch. The fronts do.
 

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I’m just thinking that there is either air still in the rear circuit or a problem somewhere in the rear circuit. Low mounted master cylinders are indeed one application where residual pressure valves are necessary but not the only application.
I always though a residual valve was for hot rods with the master cylinder mounted under the floor board real low.
 

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Discussion Starter #19
Feels like air, but I have bled the master many times then the rears over and over. Could this be as simple as needing to scuff up the shoes and drums?
 

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Discussion Starter #20
I feel the combination valve is wrong. Maybe a disc/disc unit in error was provided to me. Or the rear section of this master is defective.
 
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