Dual master cylinder f100 brakes
 

Using a dual master cylinder with f100 drum brake front and rear.

Master cylinder is a 1" bore from a AMC product.

Of the 2 ports, which is front and which is rear or does it matter?

With this style master cylinder, are inline residual valves needed?

Re: Dual master cylinder f100 brakes
 

When I installed a drum/drum AMC master cylinder on my Merc. years ago the master cyl. had the residual valves built in and no others were required.

Re: Dual master cylinder f100 brakes
 

A word of caution: A dual master cyl. conversion such as this may not work as intended! If pressure is lost front or rear, the pedal will go nearly to the floor before the remaining brakes engage. If total pedal travel is anything less than the OEM application, you will lose all braking and probably crash!
Save your neck and your car by testing your setup. When everything is hooked up and bled, you likely will have good brakes with little pedal travel. But now, open a front bleeder screw and try a panic stop. If the rear wheels don't slide and the pedal goes all the way to the floor, the system failed. Time to re-engineer! Repeat on the rear brakes and the fronts must lock up or again, fail.

Re: Dual master cylinder f100 brakes
 

That’s interesting ....
You think your adding a safety factor in you car and you’re creating a hazard...
A friend had that very thing happen on his old Willy’s pick up...
I’ll show him this post ...
Your learn something new here,,thanks for your input..
Carl...

Re: Dual master cylinder f100 brakes
 

I put a dual master on my 34.
The important question is what diameter master are you taking out.
If the diameter is smaller it will take more pedal travel to push the same a mount of fluid to stop the car so diameter is a big fact.
Second I put residual valves is both lines at the master to hold the fluid on the wheel cylinders so the pedal is always firm.
Third the hole closest to the mounting flange is internally valves for the front brakes
Good Luck

Re: Dual master cylinder f100 brakes
 

Is this on all dual master cylinders or disc./drum (larger resivor for the disc)?

The one I got is for drum/drum

Re: Dual master cylinder f100 brakes
 

Is this on all dual master cylinders or for disc/ drum (larger resivor for the disc) ?

The one I got is for drum/drum.

Re: Dual master cylinder f100 brakes
 

It doesn’t matter what the master was made for it matters what the piston diameter is.
Different cars and trucks used different diameter wheel cylinders .
If your new master was bigger than what you took out that would be ok , but if the diameter is smaller the pedal will have to go down further to stop the car


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Re: Dual master cylinder f100 brakes
 

The larger resivor is for disc brakes because there pistons are bigger and need more fluid

Re: Dual master cylinder f100 brakes
 

The dual master is a wise upgrade, but it has to be able to full stroke before the pedal bottoms out for it to provide the added safety, something many still don't fully understand. :)

Re: Dual master cylinder f100 brakes
 

Yes I understand that,

The question was, the port closest to the mounting flange goes to.the front brakes on all dual master cylinders for both drum/drum or drum/disc

Re: Dual master cylinder f100 brakes
 

All drum/drum masters are not 50/50 in operation, so knowing the correct primary/secondary or front/rear plumbing is important. The port (hole) closest to the mounting flange is NOT always intended for the fronts.

Re: Dual master cylinder f100 brakes
 

Yes the first piston is the primary piston for the front brakes whether disc or drum.

John

Re: Dual master cylinder f100 brakes
 

Well with the last two post,
Anyone know which port on a 1970 AMC drum drum master cylinder goes to the front brakes?

Re: Dual master cylinder f100 brakes
 

NO, NOT always. Bad information.

Re: Dual master cylinder f100 brakes
 

Yes, seem to recall that there are two springs in the piston assembly and the weak spring side is the one that goes to the front, which activates the fronts first and when the fronts are pressurized the second (strong} spring collapses to activate the rears.

Re: Dual master cylinder f100 brakes
 

It is usually the front port to the front brakes, but I would check with a brake shop or find a diagram on line for that cylinder. On a disk/drum master cylinder there is a large and small area for the fluid--large is for the disk brakes. This large area is in the front of the cylinder. On a drum/drum cylinder both areas for fluid are the same size. I used a '67 mustang drum/drum cylinder on my 39--worked OK. I think the AMC cylinder is the same except the ports are on the opposite side.

Re: Dual master cylinder f100 brakes
 

Need to know too, using a '70 Javelin master in my 32 chassis. Their disk/drum master has the large reservoir closest to the booster. May not apply for drum/drum.

Re: Dual master cylinder f100 brakes
 

Here is a '67 amc vehicle which clearly shows the port near firewall is being used for the front line; split for left and right.

Re: Dual master cylinder f100 brakes
 

That's a pretty cool master cylinder with the brake lamp switch in the bottom. Would come in handy for later swaps too that used the same switch.

Re: Dual master cylinder f100 brakes
 

Here’s the AMC/Jeep master cylinder for drum drum applications

https://www.ebay.com/itm/Brake-Maste...sAAOSwtVdbliit

Re: Dual master cylinder f100 brakes
 

Good posts; I found that the '62/3 Cadillac dual drum/drum used the same large brake tubing as the '39/48 Ford. worked for me. Newc

Re: Dual master cylinder f100 brakes
 

So, can we pretty much agree now to use the port closest to the flange for the front?

Re: Dual master cylinder f100 brakes
 

Going out on a limb, that's how I will plumb mine. I have a couple AMC guys I can check with this week.

Re: Dual master cylinder f100 brakes
 

Actually, the size of the pistons doesn't matter, as the system is filled with fluid to begin with, and piston travel is very small. The need for a large reservoir is because disc brakes have no adjustment for wear. As the pads wear, the piston extends further out, but does not retract. So fluid level in the master cylinder goes down. With a small reservoir, the master may go empty before the pads are fully worn (if no one tops it off in the meantime).

Re: Dual master cylinder f100 brakes
 

If you purchased your master , even name brand , thru Amazon it does not have residuals in it . You can usually tell by looking . Speedway sells a dual with residual valves .

Re: Dual master cylinder f100 brakes
 

Piston size does mater, and is why disc/drum and most drum/drum masters are not 50/50 in fluid displacement output. The different primary/secondary port fitting sizes prevent the front and rear OE circuits from being switched.
You are correct that caliper pad wear is one reason the disc reservoir is larger than the drum.

Re: Dual master cylinder f100 brakes
 

Can you post a link of drum/drum master that has built in residuals?

Re: Dual master cylinder f100 brakes
 

my 89 diesel dodge has the big tank to the rear, near the flange, and the small tank to the front, which is feeding the rear drum brakes. i know this because it leaks on a rear wheel cyl. need to fill every 3 months, gonna get to it one of these days

Re: Dual master cylinder f100 brakes
 

Drum/drum and (drum circuit) disc/drum masters had factory internal residuals up to the early to mid '70s, but that's no guarantee today's rebuilds have them installed. Easy to check at the parts store. :)

Re: Dual master cylinder f100 brakes
 

So there is a chance the one I got doesnt have the residual valves. How do you tell ?

Mine was made in China for dorman products.

Both ports on this one is 1/2" fine thread.

Re: Dual master cylinder f100 brakes
 

GENTLY inserting a small diameter object will detect an internal residual, which is a small spring loaded rubber check valve.

You may have a "generic" master because the OE AMC would have two port thread sizes, not one.



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Re: Dual master cylinder f100 brakes
 

I can stick a piece of TIG wire clear to the centerline of the casting. I assume there is not residuals in mine. If any doubt, I would run 2lb residual valves, one for each wheel cylinder, correct?

Re: Dual master cylinder f100 brakes
 

Run one external 10 lb valve close to the master cylinder for each drum axle if none are internal. The 2 lb valve is strictly aftermarket and should only be used for disc axles when the master is below the floor or lower than the calipers.

Re: Dual master cylinder f100 brakes
 

Aw, yes i had the 2lb and 10lb valves switched in my head. Thanks for the clarification Bob.

Re: Dual master cylinder f100 brakes
 

This one does.
Cardone 10-1292

Re: Dual master cylinder f100 brakes
 

Correct. I think a lot of people, just expect it to work because "its a dual setup"

Re: Dual master cylinder f100 brakes
 

I checked the Dorman master cylinder that I have and it does not have the residual valve.

The original single circuit 40 ford master cylinder has a check valve in the base of the bore. Does that serve the same purpose of a residual valve?

Re: Dual master cylinder f100 brakes
 

Yes.

Re: Dual master cylinder f100 brakes
 

I think I know where you are trying to go with this, but what you are saying is not totally true. A large bore, will require more fluid to move a given distance. And hydraulic pressure is created by the ratio of the different bore sizes; MC to WC or caliper.
To me the most alarming thing happening today, is these drum drum vehicles are being used with MC with different size reservoirs and no residual pressure valves. Typically a large/small reservoir on a MC means it is disc/drum. When you see a large reservoir you can count out a residual valve and even the opening for fluid flow will probably be larger. You loose some engineered brake bias.