Dual master cylinder f100 brakes

[Branded]

Originally Posted by 5851a

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.

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

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

[Newc]

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

[skidmarks]

Originally Posted by big deuce

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.

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

[big deuce]

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

[40 Deluxe]

Originally Posted by Pete F

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

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).

[Ggmac]

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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 .

[V8 Bob]

Originally Posted by 40 Deluxe

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).

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.

[big deuce]

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

[cas3]

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

[V8 Bob]

Originally Posted by big deuce

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

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.

[skidmarks]

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.

[V8 Bob]

Originally Posted by skidmarks

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.

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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[big deuce]

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?

[V8 Bob]

Originally Posted by big deuce

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?

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.

[big deuce]

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

[Branded]

Originally Posted by big deuce

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

This one does.
Cardone 10-1292

[Talkwrench]

Originally Posted by 40 Deluxe

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.

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

[skidmarks]

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?

[V8 Bob]

Originally Posted by skidmarks

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?

Yes.

[PetesPonies]

Originally Posted by 40 Deluxe

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).

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.