dual master conversion

my 66 a100 has a slow leak in the brake master cylinder - would like to convert to dual type - what all does it take to do so - oo3

I don't think I ever read anything on doing one on a A. But I bet one of the Dodge guts here knows all about it.

its not too hard to do, you will need to change the brass equliser with a late model 67-70 model van or any dual master drum brake mopar, you will have to trim the radiator houseing mount bracket and radiator housing to accomadate the longer master cyl. how are your brake lights hooked up is there a switch on the pedal or a pressure swich ?my 65 has a pressure switch - not sure what they used in 66 mabee Nate would know,..

looks like i have a pressure switch - i know there was some info on the yahoo a100 site - but with my main computer down i lost my bookmark and i can never remember the link - and even when i try and google it i seem to come up with a different yahoo a100 site with a bunch of ad postings? - anyways it would be good to have this info over here maybe even in the how to section - oo3

Hey oo3:

You may have to sign up to the site to see the pictures, but it's worth it. Nate did a very good job and makes it pretty clear. He said to use a distribution block from a bone yard. I dont know if thats required. Maybe to balance the pressures? I thought you can just make a splice to the rears and plug a port in the original distribution block.

http://www.dodgetalk.com/forums/showthread.php?t=49930&highlight=master+cylinder

Rockauto.com shows some master cylinders for '68s, but I don't know if they are OK to use (too tall?).

The mechnical switch should be easy to connect to the pedal. Hot rodders use them.

all dual systems should have a proportioning valve somewhere. usually just beside or below the master cylinder. find one , get one. where your master bolts on usually has the bigger resiovoir and that side is for the front brakes and the smaller one furthest away from the mount flange is for the rear brakes. your valve should have 4 fittings, 2 from the master, and 2 out to the wheels, front and rear. do what donivan65 said replace all lines now and you should have 2 lines to hook up from the wheels and two from the master into the valve when ready. might take a while to bleed but a better brake system it is.proportioning valve from an 80's to early 90's half ton pickup should be fine. brake lite switch for the lights means be creative and look under the dash of some junkers to see how they hookup and adapt that to your truck.

It's my understanding that dual master cylinders with one larger reservoir and one smaller are for vehicles with disc brakes up front, circa 1967 up.

A dual master cylinder for all drum vehicles will have two reservoirs the same size, and there is no need for a proportioning valve because all four wheels will take the same pressure. You can use one with mismatched size reservoirs, but you don't need it.

If you're adding discs up front, then you need a proportioning valve hooked to the rear drums to throttle the pressure going to the rear drums or they will lock up before the front brakes. Factory proportioning valves are designed with the vehicle they came from in mind. So if you install one from a large truck, it's not right for a small light van. An aftermarket adjustable one is what you should install, so you can fine tune it to the vehicle, espcially true if you're carrying a load in the back of your van.

How to plumb the front lines. These photos are using an open junction block, not a factory proportioning valve. If your junction block is not open inside, this won't work!

OLD CONFIGURATION


NEW CONFIGURATION

Bore size is important too. The smaller the bore, the easier it is to push the brake pedal down. Personally I like a nice hard stiff pedal, not a soft spongy one...so 1 1/8" bore is good. Master cylinders designed for use with a brake booster are usually smaller bore, like 15/16".

Okay, you might be right about "Master cylinders designed for use with a brake booster are usually smaller bore, like 15/16". Only certain years of Mopar MC's fall into this category. I believe '73-76 dual mc for power brakes.

But, I still maintain that a smaller master cylinder piston will exert more line pressure with the same amount of force (pedal ratio) than a master cylinder piston with a larger piston area. That means the smaller bore makes for a lighter pedal.

If you're reading this, do your homework and don't depend on what either of us are saying as Gospel.

I'm just going with some known Mopar stuff I've read and used on my '65 Barracuda. I upgraded to discs on it, along with a dual master and an adjustable proportioning valve. I used a 1 1/8" bore master and it's got a nice stiff pedal, the way I like it.

Also, I believe in 1967 Dual master cylinders were mandated...if that's the case, there must be a dual master that will fit into the small space of where my single one currently is, right? Without body modification?

some schooling on pascal's law is in order i guess.????

I might be off here, but if you put 100 lbs of pressure on a 1" bore you get 100 divided by 3.1415 (pi x 1" dia.) = 31.83 lbs/sq inch. 1 1/8" bore gets you 100 divided by 3.534 (pi x 1.125" dia.) = 28.29 lbs/sq inch.

Does that still apply to the master cylinder funneling the fluid down to a 5/16" tube? Common sense would seem to suggest that 100 lbs of force applied to the master cylinder still transfers (almost) 100 lbs of force to the 4 wheel cylinders (or calipers).

The bore diameter might only affect the sensitivity (or modulation) and pedal travel because you can only shoot so much fluid into the wheel cylinders.

A larger bore may be required to displace the much larger piston in the caliper without having to lengthen the stroke.

Literally flunked H.S. Physics, but this stuff gets me going.

bottom line is - you want a dual master cylinder make a couple changes in your plumbing add a proportioning valve and a dual master cylinder. you will get used to the feel of the pedal. most masters come with residual valves in place ,just look in the fitting holes. the proportioning valve will shift if you break a line or hose and still give you some breaking albeit reduced if it is working at all. they also have the switch for a system malfunction, that lite on the dash somewhere. consult PASCAL'S LAW under google for the mathmatics to deterime the pressures at the master and wheel cylinders.

Unless your converting to front disc / rear drums, you don’t need a Proportioning Valve. The four-drum setup with a dual master cylinder takes a Distribution Block, often confused with the Proportioning Valve.

On the 2nd Gen. Chevy’s,
Brake fluid enters the Distribution Block from both ends from the master cylinder. The front brakes are fed from one side of the Distribution Block, and the rear brakes are fed from the other. In the center of the valve is a barbell looking piece that slides to the low-pressure side of the valve. If the pressure drops on one side it slides and makes contact with a switch that causes the dash brake light to light up.




Although I’m not a Dodge / Fargo owner, it seems to me that the setup would be the same.

(Insert Homer Simpson impression here) DOOH!

Area of circle = Pi x r squared , NOT Pi x diameter (you idiot, no wonder you can't seem to make any money)

Sorry guys.

Here's some mental exercises for you:
http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/Pascals_principle.html

i see that cardone 101323 mc comes in regular or power brake version - and it is for 67 and later vans and other cars also - lots of great info thanks - i will start getting my pieces together - nate if you check in any chance you could post those pics from the dodgetalk forum here ? - oo3