Single to dual M/C. Some specific queries

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TimDart

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Hi all, I know this subject comes up, but I have found contradictions at times. I’m in the UK so really need to order the correct parts just once.due to shipping and taxes etc..
Car- 1966 Barracuda Formula S with stock10” drum brakes all round.
What to buy?
I’m thinking a 1967 master cylinder for all 10” drum brakes ( the easy part)
I want to use my original distribution block and am wondering what size plug I need to block off the rear brake port?
I assume new brake line from front of m/c to rear brakes?
Final query is which ports connect the front brakes from the distribution block. That’s really the part I need to get right as the shop doing the job need to know.
Thanks for any help, after a low mph brake fail with the single system I never want to be there again
 
The purpose of the dual M/C is to isolate the front from the back brakes in case of failure. The dual M/C should be used with it's companion distribution block, not modify your old block to work with the new M/C. Some modification of remaining brake lines (or purchase new ones) will be needed.
 
As I understand it, the old distribution block can be used as the rear brakes are supplied entirely from the new master cylinder. This allows the existing distribution block to be used for the front brakes. I just need to know which port supplies each front brake and what size plug is used to block off the rear supply.
 
Murray said:
The purpose of the dual M/C is to isolate the front from the back brakes in case of failure. The dual M/C should be used with it's companion distribution block, not modify your old block to work with the new M/C. Some modification of remaining brake lines (or purchase new ones) will be needed.
Click to expand...
The only difference in what he is asking and they way it is done is not having an idiot light for the brakes.
The distribution valve on the 67+ has a switch between the front and rear circuits to detect a difference in pressure.
Running the rear brakes directly to the master cylinder would impact function just not having provisions for the idiot light.
The dual master alone is where the safety is done.


Alan
 
The newer distribution block does more than "detect" a difference and turn on a light. In the event of failure, a metal "piston" moves in the failure direction and blocks any flow of fluid to the now damaged line, not allowing any wasting of the fluid. This movement of the "piston" also grounds the warning light switch cause it to complete the circuit and now go on. The OP can hook up his M/C any way he wants too.
 
Murray said:
The newer distribution block does more than "detect" a difference and turn on a light. In the event of failure, a metal "piston" moves in the failure direction and blocks any flow....
Thanks for the info. Is the distribution you refer to actually a proportioning valve, or just an uprated distribution block?
I was under the impression that the dual master cylinder provided sufficient circuit protection if one side fails.
I’m here to learn. If I keep my existing block does anyone know what size plug is needed to block off the rear port as I need to find that?
Click to expand...
 
Sorry, posted without completing...
I wish to retain the current block as it works and I understand that some of the aftermarket distribution blocks are of questionable quality.
Can anyone point me to the correct size plug so that I can block off the rear brake port at the block?
 
If you do not install the block that @Murray is talking about , ignoring the light feature for a second, then, there is almost no point to installing a dual-reservoir M/C.
1) you have to isolate the front and rear systems
2) you have to split the fronts to left and right. This has already been done for you by the factory
3) the dual piston M/C has two hydraulically separated chambers. that are interconnected by a third center chamber.One of the end chambers is connected to the front brakes and the other to the rear.
How it works
When everything is working right
You step on the pedal and the rearmost chamber drives the front chamber hydraulically thru the interconnecting chamber. Fluid goes out ,and the brakes apply.
Now
if either the front brakes fail or the rears fail, then fluid still goes out. But whichever end has failed does not apply the brakes on that end and instead, the fluid ends up on the ground.
But when one end suffers a fluid loss, something inside the M/C changes. The hydraulic chamber in the center no longer works, So instead, the manufacturer has designed one of the pistons with a button on it so that it can still reach the other piston.
However, the loss of the center chamber means that the pedal moves way lower in it's travel scaring the chit out of you. KEEP PRESSING!, the still working brake will eventually be activated.
Below is the valve @Murray is talking about. As the differential valve moves sideways, it covers and closes off the failed section. If it didn't do this, you would eventually pump all the fluid out of the failed-side reservoir.
The fact that this differential valve turns on the dash-light is somewhat irrelevant/redundant, because it is readily apparent that something has changed and your brain will tell you all about it.
Do you absolutely need it? I think yes because with the failed side closed, I think your pedal height would have to return after one or two brake applications.
master-brake3.jpg


combovalve-gif.gif
 
AJ, thanks for taking the time to post all that detail, I really needed a full explanation and thanks to Murray for his idea too. Now I understand and will purchase both the dual MC and the matching distribution block.
Much appreciated, I can assure you
 
yur welcome
To help is what most of us are here for.
Typically the frontmost reservoir feeds the rear brakes.

I know a lil about cars
a lil about God, and
at 68 I'm learning all about living out the promises.
 
I re-used the distribution block in my 1964 and 1965 Mopars (Valiant, Dart, Newport). The existing feed from the MC is a 1/4" tube to the top port of the block. I put an inverted flare adapter (1/4 M to 3/16 F) in that port since all dual MC's use 3/16" tubes. I plugged the port to the rear brakes. I used an inline coupler to connect the new 3/16" tube from the front MC port to the existing rear tube. I plumbed an adjustable proportioning valve ($30) to the rears in case I later switch to front disks. All adapters were bought in bubble packs at Autozone. I posted the PN's in the past, if you care to google.

In all 3 cars, I used an MC for a 1999 Breeze w/ ABS. One MC is mounted to a 1990's booster for an Intrepid, mounted on Dart firewall brackets (avatar). Another has a 2-4 bolt adapter plate to mount to the C-body booster. Another uses the adapter plate straight to the firewall (manual brakes), using the existing brake rod (w/ new rubber lock bushing) and the pedal wound up in the same place. Most people here use the 1980's Dodge truck MC, which Dr Diff sells w/ adapter plate and custom smaller bore (for easier pedal). The Breeze MC has a 7/8"D piston and 2 regular inverted-flare ports. I wouldn't use the 1967 MC since they slosh fluid out to remove paint from the firewall, and thus let moisture in, plus cast-iron is heavy and looks ugly to me, but some people prefer them as they do their wives (avoid those photos).

I don't have a pressure-imbalance switch in any of mine. I'll bet most vintage ones had the piston rust in-place to no longer work (my 1969 Dart gave no warning). You can buy new "combination valves" with one (~$70). If you do, wire it in parallel with your e-brake lamp, to connect to ground when actuated, which you can also do for a reservoir level-sensor. That is how my 1996 Plymouth is wired. Any of the 3 will light the "brake warning" lamp.
 
TimDart said:
Hi all, I know this subject comes up, but I have found contradictions at times. I’m in the UK so really need to order the correct parts just once.due to shipping and taxes etc..
Car- 1966 Barracuda Formula S with stock10” drum brakes all round.
What to buy?
I’m thinking a 1967 master cylinder for all 10” drum brakes ( the easy part)
I want to use my original distribution block and am wondering what size plug I need to block off the rear brake port?
I assume new brake line from front of m/c to rear brakes?
Final query is which ports connect the front brakes from the distribution block. That’s really the part I need to get right as the shop doing the job need to know.
Thanks for any help, after a low mph brake fail with the single system I never want to be there again
Click to expand...
You will find a thread in the How to Articles.
 
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