So i have done some searching around on past threads and found some decent info but still a little confused. I have a 66 F250 and i am keeping the drum brakes all around. I have upgraded to a dual master cylinder. Now, i have seen everywhere people are quite adamant that a proportioning valve is not necessary as it is intended for disc/drum setups (from what i can tell....) The issue i am having is a lot of the terminology that is being thrown around in the threads flat out doesn't exist when you google it....So that being said, what the hell do i need?? I understand larger chamber of the MC should operate the front brakes, smaller chamber the rear but beyond that is all i need a simple T fitting on each "circuit" to run to the left and right side? Also, i have an electric pressure switch but saw in a thread someone mentioned a hydraulic switch. Could someone point me to a part number? Any part #'s, links or pictures would be appreciated. Thanks!

 

Welcome to FTE. Dual master cylinder for 4 wheel drum brakes should have equal sized chambers. Yes to a pair if Tee's. The hydraulic brake light switch bolts into the master or a tee coming off the master. What a lot of guys are doing is adapting a mechanical switch that works off the pedal like a later model. Dan

 

You're right, a proportioning valve is not necessary, but it can be useful. You can adjust the valve to allow full pressure when the truck is loaded, and to limit pressure when it is empty, so the rears won't lock prematurely. The manufacturers added similar valves to their pickups years ago, although those were adjusted automatically according to ride height.
I'll be doing the same job soon. I have a '67 dual master and the basic (cheap) Wilwood valve.
Eric

 

I did this swap about a year and a half ago. Besides the conventional brake stuff I bought the master cylinder, 2 brake line tees, and a new hydraulic switch.

You need 1 tee to connect the master cylinder to the front left/right wheels, this replaces the 4 way block that's there now.
The other line from the master cylinder goes to the rear axle, where there is already a tee going to the left/right wheels, I reused this one.
The other tee just allows you to connect the hydraulic brake switch, the type your truck has now inline.
Examples below

I did not use a proportioning valve but others have as mentioned. I also went ahead a replaced all the hard lines and hoses, this is a good time to.

 

Awesome, thanks for the info! Does your MC have one small and one large chamber or equal sizes like recommended above? Are you happy with your setup? Does it brake well? My truck will only be used for putting around town, nothing crazy so i am hopeful the drum/drum setup will be sufficient provided everything is adjusted correctly. I have all new lines, drums, shoes, hardware and wheel cylinders so i anticipate it to function adequately.

 

I have one from a 67 fairlane I just got it from amazon. Yeah works fine my truck is my daily driver and I haven't had any issues with braking.

 

It's not mandatory that the reservoirs be the same size. Even Ford used the later style with different size reservoirs on vehicles with four-wheel drums.

So while common in the very early days of dual/tandem masters, it's not an absolute. Probably a running change as more and more vehicles got disc brakes at least as an option, so that Ford only had to use the one style and simply change the size of the piston to suit the application.
Four wheel drive trucks and Broncos did not get disc brakes even as an option until '76 when they became standard. But they had already been using the unequal size reservoirs since at least '70.
And GM did sort of the same thing, only opposite, with their common use of the large master cylinders with equal-size (large) reservoirs starting in the late sixties, whether the vehicle had 4-wheel disc brakes (such as the Corvette) or drum/drum or disc/drums like the pickups. Same master design for all three.

This is all strictly guesswork though and I have not studied it much in detail. Just remembering what I've seen. I just know I've seen a few equal-sized reservoir setups, but a lot more with the unequal size yet still on drum brakes.
It's possible that the first year or sor of use of dual masters on Broncos they had the old style with the equal-size reservoirs, but I only remember seeing them on the full-size trucks at the time.

Anyway, just saying I don't know the situation for all applications, but that non-equal size reservoirs were indeed used on factory 4-wheel drum setups at some point. So you're good either way as long as you get all the other parameters correct.
When I swapped over to front discs on my '71 I used the existing master and did not add a proportioning valve or do anything else (other than remove the residual pressure check valve for the front) and they work great.

Paul

 

Thanks! Yeah i already have a new master so different size chambers is going to have to work haha. I dont forsee any issues, and if some pop up its an easy enough fix.

 

Sounds like you're all over it. Dual pot MC into 2 lines with a couple curls for flexibility between the body and frame, t-fitting for front and rear to feed into both sides. Rear t-fitting will be on the axle tube of course. I highly recommend using a mechanical brake light switch such as SLS66. Set it up on a simple bracket in the pedal box to rest on the pedal itself. The switch is meant to be a normally open circuit until you step on the brakes and it completes the power circuit for the taillights.