Clarification on brake set-up

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evans68cuda

evans68cuda

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I've been doing lots of research on converting to front disc brakes on a 68 barracuda that originally had 4 wheel drums and drew a picture of what I think it should look like. I just turned 20 and don't have the experience most of you guys do so if there is somthing wrong, please let me know!!! I don't have the original 4 wheel drum master so I cannot take the RPV out of that and install it in the new master, hence the RPV being added into the brake line after the master but before the distribution block. I've heard you can and cannot use this 4 wheel drum distribution block with front discs so an answer for that would be awesome, as well as where to put the adjustable proprioning valve (I think after the distribution block) already installed the brakes , just not the master or the other valves. This is also the 73+ discs and 11x2 drums in the rear. thanks guys!

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Typically the residual valve is on the brake side of the block, not the master cylinder side. Holding the residual pressure through the distribution block could mess with the brake light switch.
 
Ok first, the Distribution block is actually a proportioning valve, needs to come out. Second the "Brake switch" is not. It is a brake system warning switch, in case of loss of pressure. Brake light switch is on the brake pedal.
 
72bluNblu said:
Typically the residual valve is on the brake side of the block, not the master cylinder side. Holding the residual pressure through the distribution block could mess with the brake light switch.
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Ok, reason I put it there is because the factory put them in the master, so it was before the distribution block. But that makes sense
 
Mopar Tim said:
Ok first, the Distribution block is actually a proportioning valve, needs to come out. Second the "Brake switch" is not. It is a brake system warning switch, in case of loss of pressure. Brake light switch is on the brake pedal.
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Im thinking the Prop. Valve might be ok to keep, with adj. Prop. Valve installed.
 
Your only 20 ? Your doing damn good. Keep asking quality questions. Thats how we all learned.
 
Mopar Tim said:
Im thinking the Prop. Valve might be ok to keep, with adj. Prop. Valve installed.
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Ok so keep the distribution block and put a prompting valve behind it for the rear? From my understanding, my distribution block is mainly just to set off the warning light in case of a loss in pressure. But seems like that should be in the master cylinder so that's why I wasn't sure.
 
72Dart6pack said:
Your only 20 ? Your doing damn good. Keep asking quality questions. Thats how we all learned.
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Yep, turned 20 last month. I bought the cuda when I was 19. I put a little background on it in the garage section if you want to check it out. And thanks! Trying not to annoy you guys with questions. Just trying to avoid any idiot mistakes I can! Here's the link to my garage Evan's 68 Barracuda Fastback "The Cuder"
 
Mopar Tim said:
Ok first, the Distribution block is actually a proportioning valve, needs to come out. Second the "Brake switch" is not. It is a brake system warning switch, in case of loss of pressure. Brake light switch is on the brake pedal.
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No sir, not a prop valve. This was a drum/drum car, they just had distribution blocks. Not a proportioning valve like the disk/drum cars. The block and the adjuster to the rear will be just fine.

68cuder said:
Ok, reason I put it there is because the factory put them in the master, so it was before the distribution block. But that makes sense
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68cuder said:
Ok so keep the distribution block and put a prompting valve behind it for the rear? From my understanding, my distribution block is mainly just to set off the warning light in case of a loss in pressure. But seems like that should be in the master cylinder so that's why I wasn't sure.
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You know it probably doesn't matter. Mopars of this vintage did put the residual valve in the master. Other makes put them in the prop valves. I've converted a couple of drum/drum cars with modern master cylinders and prop valves and I just put the residual valve between the brakes and the prop valve. Keeps it under the car so you don't see it in the engine compartment.

Yeah, the brake switch isn't for the lights its for the warning light, I was just thinking it's a pressure switch so adding the residual valve so it would hold pressure through the switch could change it's function if it wasn't intended to see the residual pressure. But I forgot that the originals had the valve in the master.
 
Residual valves-10 psi for drum brakes,3 psi for disc brakes. After prop valve.
 
72bluNblu said:
No sir, not a prop valve. This was a drum/drum car, they just had distribution blocks. Not a proportioning valve like the disk/drum cars. The block and the adjuster to the rear will be just fine.




You know it probably doesn't matter. Mopars of this vintage did put the residual valve in the master. Other makes put them in the prop valves. I've converted a couple of drum/drum cars with modern master cylinders and prop valves and I just put the residual valve between the brakes and the prop valve. Keeps it under the car so you don't see it in the engine compartment.

Yeah, the brake switch isn't for the lights its for the warning light, I was just thinking it's a pressure switch so adding the residual valve so it would hold pressure through the switch could change it's function if it wasn't intended to see the residual pressure. But I forgot that the originals had the valve in the master.
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Ok, say I agree it is a just dist block. How could it function to turn on a loss of pressure light? It HAS to do more. Inquiring minds...
 
Dual master cylinders used the block with the front brakes on one end of the block and rear on the other with the warning lamp switch in the middle. When you blew a line or wheel cylinder, the valve thru loss of pressure would move the valve and ground the warning lamp wire turning on the brake light warning lamp in your cluster.
 
Mopar Tim said:
Ok, say I agree it is a just dist block. How could it function to turn on a loss of pressure light? It HAS to do more. Inquiring minds...
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upload_2017-7-29_20-43-34.png

Just a pressure differential contact to ground to warn of line breakage/pressure loss on either system..
 
Not that it matters but remember the pre 71 cars used a separate hold off valve for the rears in disc applications in line, and later models were combo units built into the distribution valve! If you are retro fitting you have to consider this. You could end up with two rear reducers if you do not pay attention.
 
SGBARRACUDA said:
With all the customizing done on our old Mopars like different front and sometimes rear disc brake set ups. Plus all the different size rear drum brake sizes. I prefer to used the Mopar alluminum style master cylinder and an adjustable brake valve to the rear lines like this one.
https://www.summitracing.com/parts/wil-260-8419
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As long as all the lines are straight through it is all good. Just remember early disc cars Had that separate valve.
 
You might have problems running 11" rear brakes and keeping them from locking up. I remember reading an article awhile back talking about the wheel cylinders piston diameter has to be a certain size when using disc fronts. I'll try to scare up some more info.
 
I run the 11x 2" 1/4" on the rear of my Barracuda with Wilwood front discs. With the adjustable proportioning valve on the rear, I've had no issues yet.
 
Thanks for the replies everyone. So its sounding like my diagram is pretty accurate? and according to 72bluNblu, I could even run it after the block and prop valve, but does not really matter? Tommorow I will be putting the 11x2 drums in the rear and looking at summit to buy the prop and residual valves. I have brand new 1 1/16" bore master that ill be trying out to see how i like the feel of! Oh and by the way, I think my rears are actually 10x2.5! the 11" drums do not fit but my old 10" do, and the backing plate offset is about 1 3/4!
 
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