Technical 4 wheel power drums

Growing up we had a few heavy cars with power drums, (my dad was a Buick man) and They always stopped decent.

I have a hypothetical build I need some clarification on. I was pondering a straight axle with self energizing F-2 styled brakes. I am thinking a dual chamber MC mounted on a small power booster.

So, just thinking it out loud here.
Is there still a need for a proportioning valve?

I was just wondering if you could just use each master cylinder chamber , for a front/rear system, in case of failure?

Or should I tie all the systems into one common line? Would this work as a redundant system or basically turn it back into a single pot master cylinder?

Thanks for the input guys.

Please no disc vs drum discussion. I have read all of those.

 

I would install an ajustable proportioning valve no matter what type of master cylinder you use.

 

Point taken, but if I have one chamber dedicated for each line, there would be no front- rear bias. Make sense?

 

On paper you would not have to have one, unless for some reason the drums up front take different amount of pressure over what is on the rear end. I dont have much experience with 4 wheel drum outside of a stock setup where all the drums matched the car. Dual chamber drum master cylinders are a thing. Most late 60 Chevy's (Camaro/Chevelle/Nova) are setup with dual chamber with drums at all 4's. Some even with factory power boosters. If you wanted power brakes without the dual chamber, you can use a remote booster off like a T bird or Chevy pickup. We have one on Taboo mounted under the floor with the stock master cylinder still on the firewall.

 

No, the dual chamber is preferred. I like redundancy.

 

I don’t think it matters until you go dual MS.

but for drum drum I think it’s called a pressure differential valve.
looks similar

 

I agree with this.^^^^ Probably going to need the adjustability. Tying the lines together seems like a bad idea. Defeats the purpose of a dual cylinder.

 

Some cars and trucks would have left front and right rear on one circuit and right front and left rear on the other circuit.

That way if you lost 1/2 the master you still had one front and one rear brake working .

unless you took the complete system off a car I would think you would still need to fine tune bias on the car your adapting this all on.

 

Then the two lines are pretty much separated and do not need to tie in. If you look at factory setups, you will see a block usually mounted under the master cylinder. On a drum/drum car its just a switch for the dash light and is simply a pass through from the fluid and they never come in contact with either.

 

That makes sense. Wouldn’t a proportioning valve just reduce the amount of volume of fluid? If it is just strictly on either the front or back system, you would just be limiting the efficiency of the system?

 

I'll be running power 4-wheel drums on my '54. MC is '68 Mustang dual reservoir and an 8" dual diaphragm booster.
'68 Mustang dual master cylinder for power brakes
Inline Tube 8" power brake booster

Brakes are stock '54 and I'm not using an adjustable prop valve. No real world results yet 'cause the car is still under construction but, I don't anticipate any issues. Several guys in our social forum have done the same.

 

A proportioning valve lets the rear brakes receive the same pressure as the front, until the pressure reaches the set point of the valve, then it limits pressure, to a lower value than the front, but still increasing proportionally.

Most OEM 4 wheel drum brakes don't have rear proportioning valves.

A dual circuit system has two pistons, one providing fluid to the front brakes, the other to the rear brakes. They both operate at the same pressure (before the prop valve, if there is one), unless there's a failure that lets one of them bottom out--then only the good side still receives pressure.

If you tie both sides together, then when there's a leak on one side, both sides of the dual MC will see the leak, and it will not function to keep the brakes working.

You do need to size the wheel cylinders to match the relative brake loads, and the best way to do this is to use brakes of the same size and with the same size wheel cylinders, as a similar weight and front/rear balance car.

Adding a power booster just makes it easier to push the brake pedal. It might be something you want to do. I learned to drive on drum brake cars, one of which had a booster, and it didn't take much for me to learn to adapt to the pedal force requirements of all of them.

 

I could be way off , but the way I see is if this is a “ built “ brake system , ie , not a complete factory system . And it’s going on a lighter car . You would need to get the front brakes applying before the rear and in a panic stop with the weight of the car getting thrown forward you would not want the rear brakes locking up .

I think , reading other posts you could install the brake system and test it out, if then you do need one it’s pretty simply to tie it into the line going to the rear brakes if needed .

 

Yes, to expound, this will be a built system from scratch. I am using the 56 Ford F2 backing plates. I figured I would match the wheel cylinders to a factory drum/drum dual master cylinder. The power booster is just for my own preference. I have some non power systems and I am at times afraid that I don’t have enough leg left in an emergency.

This hypothetical brake build is for a 36 Ford pickup that weighs roughly 3300 lbs.

Just an FYI, I bought the dual 60-62 C10,
Non power mc and still haven’t decided 100% against it. It’s Still in the deliberations phase.

Trying to compare apples to oranges.

 

The old truck dual cylinder is for a clutch pedal, and a brake pedal. Not for two brake circuits on one pedal. I figure you know that, though

 

I'm running the dual '62 Chev truck MC in my roadster. It's basically a single pot 'cause the other side controls my hydraulic clutch. '56 F-100 drum brakes up front and '75 Maverick rears. No power and you gotta lay on 'em pretty good to halt the roadster. Car only weights 1500 lbs.

 

Hypothetically since the bores are the same, could that setup be used as a dual brake MS?
I’m using a 60-62 gm truck auto MS (single pot) to work the clutch on my sons 61.
It has a hydro boost brake set up but I used an automatic brake MS to work the hydro clutch since they are the same bore. Works great

 

Yeah, but if you modify the innerds, you can use it for all brakes.

 

I'm sure you know one side of the dual 60-66 C10 master is for the clutch. You should also factor in your pedal ratio. This makes a big difference in the applied force required to generate a given pressure.

 

How would you modify it? They are essentially two separate cylinders in one casting. The only way to do it would be to tie the push rods together.

 

how would it be different than running a dual MS set up.
If ya wanted a dual MS with a vintage look, why wouldn’t the 60-62 gm truck MS work?
Just wondering

 

If you set it up right, it could be used like that....seems to me like a lot of unneeded work, but hey, that's what hot rodding is all about.

 

https://www.jalopyjournal.com/forum...t-rods-1960-62-c10-m-c.1213284/#post-13839942

This should clear up any confusion on the 60-62 mc.

 

Dual MC. Dual adjustable prop valves. One long parking lot for high speed panic stops. One buddy to watch for front/rear lockup. Keep adjusting till bias is correct and maximum adhesion is achieved.

 

I always got the brakes off of a car about the same weight as the car I was building. It has always worked out OK. The factory drum on drum systems got their balance from front to rear by having different bore wheel cylinders on each end of the car.

 

Actually, @squirrel , I misspoke.

I was remembering the swapping of the internals to make it a clutch/brake MC. Sorry COVID brain fog.

Back to your regularly scheduled programming.

 

You’re not totally incorrect. According to the link you posted, the gm side by side MS has a residual valve in the brake side. So would you have to add a residual valve to the clutch side to uses both sides to work the brakes?

 

Yeah, but I don’t want 2 brake pedals. You wouldn’t gain much from 2 pistons and 1 reservoir.

 

Just a hypothetical curiosity on my part.

 

So what am I missing here? As I understand it, you want two separate systems so if a brake line fails, you still have brakes,, correct? Using the same reservoir with two systems drawing from the same fluid source will NOT allow you to have brakes if one line should fail, that one failed line will still empty the reservoir.

Two separate systems (like a front and a rear, or a right front, left rear and a left front and a right rear) will require two separate reservoirs if you still want brakes if a line fails. You can not pull the fluid for both systems from the same source, that source has to be separated for each system.

The original master cylinders with a front and a rear reservoirs had a wall between the two systems, if one side went empty, the other side still remained full. Those style of masters also proving some brake bias, the reservoir closest to the firewall would apply the brakes before the farthest away reservoir applied the brakes. Many also had different sized lines (or it was easy to add reduced lines) to reduce the brake fluid flow to the rear drums preventing them from locking up prematurely. Most of the modern plastic reservoir masters draw the fluid for both systems from the same source until the fluid is drained from the plastic and then only the fluid in the metal housing is separate. I'm pretty sure you won't be using a plastic reservoir master, but I wanted to be sure that information was added.

You can also run two single reservoir master cylinders side by side and connect them to the same brake pedal with a cross bar through the pedal.
2 more things.
1) If the master cylinder is mounted on the firewall and it has a higher elevation then all of the wheel cylinders, there is no need for a residual valve. The only purpose for the residual valve is when the master is below the height of the wheel cylinders, it keeps the fluid in the wheel cylinders rather then allowing it to flow back towards the lower master.
2) The brake pedal ratio can determine how much effort is required to apply the brakes. Pedal ratio is determined by difference between the length of the pedal between the pedal pad (the part you foot sits on) and the point where the master cylinder linkage would connect to the pedal, and the length of where the master cylinder linkage connects to the pedal and the pedal pivot point is.
When two brake pedals are the exact same length from the pivot point to pedal pad, a brake pedal with a longer length between the point the master cylinder linkage is attached and the pedal pad is, will require less pedal effort then a brake pedal with that length between where the master attaches and the pedal pad is, being a shorter length. Gene